jUy-f^n^yr./ ^^^L AUGUST 1954 PROCEEDINGS NATIONAL SHELLFISHERIES ASSOCIATION Volume 45 PROCEEDINGS of the NATIONAL SHELLFISHERIES ASSOCIATION Official Publication of the National Shellfisheries Association; an Annual Journal devoted to Shellfisheries Biology Volume 45 August, 1954 Published for the National Shellfisheries Association by the Fish and Wildlife Service, TJ. S. Department of the Interior Washington, 1955 TABLE OF CONTEIWS Editor ' 6 Notes ..« o.o o »,» o oo,« .«o .„,,., o.,» ,„..o » Brief History of the National Shellf Isheries Association . ., . » , „ « » . » » . o a , . . » « , « . . „ « „ o . . o , „ ANNUAL COFvLKTION: Officers and Committees »» <>»..„» c. ,. o .„ - o = .» «,oa . Resolutions » = » » » » » » <. » » .. o » » a , » . =, . » « . . . . o o <. . <. » « o Treasurer ' s Report »«.,<, o .,<■ o.». »..,,.. Opening Remarks of the President of the Nat- ional Shellf isheries Association. , , . , . » . o . . , Report of the President of the Oyster Growers and Dealers Aosociation of North America. »., Annual Report of the Director of the Oyster Institute and Secretary-Treasurer of the Oyster Growers and Dealers Association of North America. » o , „,.»»»„,„<,. o,,,.. ..o .... „„o . CONVENTION S^cMPOSrJM ON VARIOUS ASPECTS OF OYSTER Oyster Setting .»..<. oo. o . ...o o. ,.,...,... ..^ oo . How to Increase Production of Seed Oysters in Connecticut oo» o. .o o .. o„ 0,0 .».«„..» o,.. o, , Observations of the Behavior and Distribu- tion of Oyster Larvae » , . o « » . o « . . » » o . . . » o . « » . Various Aspects of Oyster Setting in Mary= land o . o „ o o „ „ o o o . . o „ . o . o „ o » « . . o . . » o . o . o . . <, „ „ Setting of Oystere in Virginia. .o. ,=0 ......... . The General Pattern of Oyster Setting in South Carolina. ........... ... .............. . Oyster Setting on the Gulf Coast. .............. OTHER COFVENTION PAPERS: Distribution of Oyster Larvae and Spat in Relation to Some Environmental P'actors in a Tidal Estuar-y. ....... ... ............. . a o o o . 1 .G. FRANCIS BEA^TIN. A. F„ CHESTNUT. .J, RICHARDS NELSON. k 5 6 7 9 , . DAVID H. WALLACE. SETTOTG: .Jo RICHARDS NELSON, . ...V. L. LOOSANOFFo , .THURLOW C. NELSON, . G. FRANCIS BEATON. , ... JAY D. ANDREWS. . .. G. ROBERT LUNZ. .SEWELL H. HOPKINS, .12 .16 .19 .23 • 29 .38 ^7 .52 J. H. MANNING and H. H. WHALEY. ..56 Food Requirements of Some Bivalve Larvae.......... Y. L. LOOSMOFF^ H. Co DAVIS and p. E. CHAI^ILEY. Possible Causes of Growth Variations in Selective Setting of Oyster Larvae on Artificial Cultch ,....,.... ........... o . , The Tidal Spat Trap, a New Method for Col- lecting Seed Clams <>.. ..o ................ . Recent Advances in the Studies of the Struc- txire and Formation of the Sl:iell of Crass_- ostrea virginica. ..... .................. , On the Rate of Water Propulsion by the Bay Scallop ,.......,....,.,............,.,., Growth Studies in Venus mercenaria . ,.....,..., A Fungus Disease in Bivalve Lajrvae Notes on Fungus Parasites of Bivalve Mol- lusks in Chesapeake Bay. ............. Studies of Pathogenesis of Dermocystidiian marinum .....<,..... ^ ................ . Studies on the Effect of Infection by Dermo- cystidium marinum on Ciliary Action in Oysters (Crassostrea virginica) ........ A Haplosporidian Hyperpaxasite of Oysters. Effects of Two Parasites on the Growth of The Functional Morphology of the Aliment- ary Canal of Asterlas f orbes i and the Predation of Bivalve Mollusks Seasonal Vertical Movements of Oyster Drills ( Uro salpinx cinerea ) .................... Preliminary Experiments in the Use of Ground Controlled Aerial Photography in Inter- tidal Hydrographic Surveys .............. . 66 . .. p. E. CHANLEY. .. 8i^ PHILIP A. BLTLER... 95 . .. JOHN B. GLIIDE...106 .PAUL S. GALTS0FF...116 . W. A. CHIPMAN.. ,.136 A. H. GUSTAFSON., . .ll+O H. C. DAVIS and V. L. LOOSANOFF., ..151 .JAY D. ANDREWS.. ,.157 S. M. RAY and J. G. MACKIN...16I+ J. Go MACKIN and S. M. RAY.,. 168 J. G. MACKIN and HAROLD LOESCH...I82 R. WINSTON MENZEL and SEWELL H. HOPKINS . . . l8'4 . FREDERICK . A. ALDRICH. . . I87 MELBOURNE R, CARRIKER, . .190 ROBERT L. DOW... 199 The Use of Equipment and Techniques in Applied Shellfish Management . . . , DANA E. WALLACE. . . 209 Report on Certain Phases of the Chincoteague Bay Investigations M. F. W. SIELING... 212 Computation of Oyster Yields in Virginia. .. o.... .J. L. MCHUGH and J. D. ANDREWS... 217 Shellfish Sanitation as Related to the Export and Import Trade in Canada ................... J , R . MENZIES ... 2l+0 The Sanitary Aspect of Importation of Shell- fish into the United States RICHARD S. . GREEN. . . 2ii6 The Development of Recommended Practices for Sanitary Control of the Breading and Freez- ing of Shellfish , EUGENE T. JENSEN. . . 253 Titles of Papers Presented at the Convention but Published Else- where , 261 DIRECTORY OF MEMBERS OF THE NATIONAL SHELLFISHERIES ASSOCIATION TO APRIL, 1955 262 EDITOR'S NOTES Official Annual Publication , With the continued growth and use- fulness of the National Shellf isheries Association it is desirable that its official annual publication be given more stability by means of a permanent title, volume numbers, a uniform format, and a consistent pub- lication policy. This need is further emphasized by the increased n-'om- ber of articles published in its annual publication which are being ab- stracted for "Biological Abstracts" and which are being cited by investi- gators in published research appearing in well known widely circiilated journals. To serve this need the Executive Committee of the National Shell- fisheries Association has adopted the following official title for its publication; "Proceedings of the National Shellf isheries Association", At present reports and papers delivered at the annual convention of the Association (and not appearing in print elsewhere) and Association affairs will appear in the Association joiornal. The accurate retroactive assignment of volume numbers to pre- vious reports of the Association is impossible at the present time be- cause it has not been possible to locate a complete file of old reports or lists of titles and dates of publication of old reports. However, because the volume number of a journal should indicate, even though approximately, the nimiber of years of publication, we have checked avail- able information carefully and on this basis have assigned Volume Number ^5 to the present, publication. Briefly, the basis for this choice follows. The Association first organized in 1909 under the name "National Association of Shell- fish Commissioners" (see "Brief History of the National Shellf Isheries Association" by G, F, Beaven in this volume), and started Issuing annual reports. Dr. A. F. Chestnut writes me that he discovered the following foot note In an old North Carolina report recently "Report Proceedings Third Annual Convention National Association Shellfish Commissioners, 1911", and a similar reference to the 1912 convention. Assuming that annual reports were issued every year, except in 19^5 when no convention was held because of war conditions (Go F, Beaven, pers, com,), the pre- sent volume for 195^ would constitute the i4-5th,' annual report. Although there is no evidence showing that reports were Issued annually, it seems appropriate to indicate the duration of the activities of the Association by assigning a volume number of each year during which a convention was held. After the Association started meeting jointly with the Oyster Growers and Dealers Association in 1929> certain National Shellf isheries Association addresses were included with the addresses of the Oyster Growers and Dealers Association -under their distribution (G. F. Beaven, pers , com. ) , In addition to the I91I and 1912 reports cited by Dr^ Chestnut, thife following dates of puJjlicaxion of the annual Association reports have been made available thi'ough the courtesy of Dro Paul So Galtsoff and Mr, J, Richards Nelsorio In mimeographed form° 1931^ 1932, 1938? 1939^ 19^1^ 19^2, 1943, 19kk', in mimeographed form and bouiid: 19^6, 19^7? 19^8^ 19^9; in mimeographed form and paper bound; 19!?05 processed and paper bound: 1951,o 1952 j, 1953 » These reports have appeared under a variety of titles; "Preliminary Notes o 00." , ''Some Convention Addresses", "Convention Addresses", "Convention Papers", ''Papers and Discussions", "Addresses", "Papers", and "Proceedings", So far as is known these publications have all "been edited and distributed by the Secretary of the Association, Starting with the "Convention Addresses" of 1951 "the publication has been processed. Volumes for 1951 a-'id- 1953 were published by the Fish and Wildlife Service, U, S. Department of the Interior, for the Association, and publication costs were supported jointly by the Association and the Service, The volume for 1952 was published by the Chesapeake Bay Institute and financed jointly by the Oyster Growers and Dealers Association and the National Shellfisheries Association^ the former organization bearing the major printing costs. Note to Contributors , Reports and papers delivered at the annual convention of the Association, and not appearing in print elsewhere, will be accepted for publication in the "Proceedings", These, typewritten double-spaced, should be mailed to the Editor prior to the convention, or handed to him during the convention. Carbon copies are not acceptable. Only scientific names should be underlined. Foot note material should be incorporated in the text. Items of literature cited shoiold all be made consistent as to order of author's name, date, subject title, name of publication, volujie, and pages. Reference to literature citations in the text should be made by author and year, as "Smith (1955)"'' Authors are urged to punctuate and proof read carefully. The use of illustrations is encouraged. These should be reduced to a size to fit on paper 8 x 10| inches with ample margins | photographic copies are preferred to originals. Illustrations smaller than page size shoTild be loosely attached to plain white paper, preferably with rubber cement, and the legend typed in the proper position under the illustration. More than one illustration may appear on a sheet. If the illustration is page size, the legend should be typed on plain white paper and loosely attached to the illustration in the proper position with rubber cement. Wo illustrations should appear on text pages. Every paper should be accompanied by an author's summaxy, complete in itself and understandable without reference to the original article, for submission to "Biological Abstracts" by the Editor, Prompt submission of manuscripts will make possible the early publication of the "Proceedings". Stencils ajid plates used in the reproduction of the "Proceedings" will be retained for one year*. Reprints can be made at cost, expense to be borne by the author, for as many copies as the life of the stencils will permit. Those authors who desire reprints from the 195^ "Proceedings" should com- municate with the Editoi', BRIEF HISTORY OF THE MTIONAL SHELLFiSHERIES ASSOCIATION Go Francis Beaven Maryland Department of Research and Education, Solomons, Maryland During the early years of the present centur-y a need was felt for a national organization wherein those state aM federal officials charged with conserving and administering the extensive shellf isheries of our nation might meet, exchange ideas, and gain information from scientists who were studying biological and sanitary problems related to the industry. The first organizational meeting was held in New York City on January I5, I909, and on May 5 of that year a constitution and by-laws for permanent organization of a National Association of Shell- fish Commissioners was presented. Successive meetings attracted increasing attention not only from the officials of the various states but from many interested scientists and leading representatives of the industry as well. As more scientists in the fields of fishery biology, sanitation, and nutrition became active in the work of the Association a revised con- stitution and by=.laws was adopted on August 19, I93O, renaming the organization the "National Shellf isheries Association", a title more descriptive of the wide though related interests of its membership. The first joint meeting with the Oyster Growers' and Dealers Association of North America was held in I929. In 1937 the Oyster Institute of North America became a part of the Annual Oyster Con- vention. Highly successful joint meetings of the three organizations have been held in major cities along the Atlantic Coast each year which have been centers of attraction for all people concerned with shellfish. The National Shellfisheries Association is felt to be a unique organization in that fishery administrators, business men, and fishery biologists here meet on common ground and discuss their problems to the mutual advantage of each. Up to the minute reports on the latest research dealing with shellfish are brought to the attention of admin- istrators and practical men of the industry. All such reports and addresses made at Association conventions, during recent years have been printed and distributed to members. The growing membership of the Association attests to the values derived from its proceedings. BOSTON MEETINGS The Annual Convention of the National Shellf isheries Association was held this year in the Sheraton-Plaza Hotel, Boston, Massachusetts, August 1-5^ 195^; jointly with the Oyster Growers and Dealers Association of North America, Inc., and the Oyster Institute of North America. The following officers and Executive Committee served during the year 1953-5^^ and were re-elected to serve for the year 195^-55- Other Committees ser- ved during the year 1953 -5^ • Officers, 1953-55 President : A. F. Chestnut, Institute of Fisheries Research of the Univer- sity of Worth Carolina, Morehead City, N. C. Vice-Pres ident ; G. Francis Beaven, Maryland Department of Research and Education, Solomons, Md. Secretary-Treasurer and Editor : Melbourne R. Carriker, Department of Zoology, University of North Carolina, Chapel Hill, N. C. Executive Committee, 1953-55 A. F. Chestnut G. Francis Beaven Melbourne R. Carriker James B. Engle Other Committees, 1953-5^ Program Committee ; V. L. Loosanoff, Chairmanj Eugene Cronin, Jo G. Mackin, "T". R. Rice, David H. Wallace. Resolutions Committee : Melbourne R. Carriker, Chairman; J. L. McHugh, J. B. Clancy, J. N. McConnell. Convention Committee : G. Francis Beaven, Chairman; Harold H. Haskin. Nominating Committee : James B. Engle^ Chairman; John Glude, G. Robert Lunz. .4- Resolutions The following resolutions submitted by the Resolutions Committee were unanimously adopted by the Convention; WHEREAS the Congress of the United States has recognized the im= portance of the sea food industry and the vital need for expanding re= search to aid in studies for unsolved problems with which this industry is faced by passing the Saltonstall Bill, and WHEREAS the shellfish industry is an important segment of the seafood industry^ and WHEREAS the shellfisheries face a number of urgent problems that are not now being adequately investigated, THEREFORE be it resolved by the Oyster Growers and Dealers Association and the National Shellfisheries Association in convention assembled that the U. S. Fish and Wildlife Service be respectfully \xrged to give due consideration to the urgency of the problems now facing the shellfish industry by allocating f-unds for vigorous and sustained re= search \mder the provisions of the Act. WHEREAS Mr. Marcus Urann, Cranberry Canners, Inc«, and Mr, Nelson Blount, President Blount Seafood Corporation, kindly arranged for a fine New England clam bake and trip on the Edaville Railroad, and gifts of cranberry products for members of the convention and their guests, and WHEREAS Mrso Otto Alletag and Mrs, Byron Blount, co-chairmen of the Ladies Committee, provided an enjoyable program of entertainment for the ladies, THEREFORE be it resolved by the Oyster Growers and Dealers Asso= elation and the National Shellfisheries Association in convention assembled that sincere and heartfelt thanks be expressed to these ladies and gentle- men. WHEREAS Mr-, William McClain, Vice-President of the Oyster Growers and Dealers Association, has been a faithful and active participant in our conventions for so many years, and WHEREAS because of illness he has been unable zo attend the 195^ Convention in Boston, THEREFORE be it resolved by the Oyster Growers and Dealers Asso- ciation and the National Shellfisheries Association in convention assembled that good wishes be extended to Mr. McClain for a speedy recovery. =5' Report of the Treasurer of the National Shellfisheries Association for June, 1953 to August, 195^ Balance on hand as of June, 1953 • ,.......<,.. $517.05 Dues collected to date for 195^-55 and arrears o.... o... 177-00 Total income „ „ 694.05 Expenditures since June, 1953 ....<.. 252«47 Balance on hand as of August, 195^ « » $UUl. 58 -6- OPENING REMARKS OF THE PRESIDENT OF THE NATIONAL SHELLFISHERIES ASSOCIATION Ao Fo Chestnut Institute of Fisheries Resestrch, University of North Carolina, Morehead City, North Carolina It is a distinct pleasure for me at this time to extend a sin- cere welcome to the members of the National Shellfisheries Association, our friends, and guests gathered at this annual meeting,. We have come a long way since our meeting last year, from the placid GilLf coast to this rugged, rock=Too\md New England coast » I Relieve this to be the first occasion of a meeting of this Association in Boston, thoijgh not the first in New England. Some years ago this Association met at nearby Woods Hole, Massachusetts, and more recently in Providence, Rhode Island, and in New Haven, Connecticut „ We look forward each year at these meetings to the renewing of acquaintances, meeting new friends, and to the serious, informal dis- cussions and exchange of ideas, information, and future plans, as well as to the lighter moments of good fellowship. To many of us this is the only time of the year we have occasion to see our fellow scientists and friends and at the same time to be brought back into the realm of practicality in meeting with the members from industry. Those of us concerned with the official duties of the Association have a feeling of optimism as we look back over the year Just past. Our Association has grown in numObers and is receiving wider recognition than ever before. We are a small group of specialized workers in a field that is growing. Our membership has nearly doubled in the past five years and the prospects for a much gr-eater growth are bright. Our members come from a mmber of various fields. Slightly over half are scientists act= ively engaged in research in this specific field, while the remaining members come from the closely related fields of public health, sanitation, conservation, management, axid those with an. active interest in what is being accomplished. Our increase in membership has brought about a greater regional distribution. Members were recently added from the west coast, thus more nearly fulfilling our title of a national association. In relatively recent years the centers of shellfish research have been more or less limited to the Chesapeake Bay area and northwai'd. Today each coastal state from Maine to Texas and,, on the west coast has programs ov varying intensity underway. It would be a difficult, if not Impossible, task to single out any specific locality as the most important center of shellfish research. The contributions from the Gulf coast are as impor= tant as those from the Middle and South Atlantic states. There is evi- dence of this at these meetings. Nearly half of the speakers to be heard in our technical sessions are reporting on research efforts made in the south o The contriTautions of many of our members have been outstand- ing through this past year and are too numerous to list. The diver- sity of research endeavors is evident in the program we are to hear. More attention is "being devoted to studies of other species, such as the soft clam, Mya , and the hard clam, Venus , than in the past. Greater emphasis is being placed upon the new avenues of research that have been opened up, particularly on fungal parasites and the ciilturing of larvae. I want to call the attention of our membership to two matters of importance. Our Association operates on very modest funds derived from equally modest membership dues, too modest to maintain or support a reputable publication. This is most unfortunate since many papers presented at these meetings in the past never appeared in print else- where, and thus were lost to science. In the last few years we have been more fortunate in receiving aid in processing our proceedings. This aid has come from several soiorces and we are indeed appreciative. We have been able to progress from mimeographed accounts of our meet- ings to a more finished processing of the papers presented. With this precedent the demand for copies from various libraries has greatly in- creased, and an international distribution has resulted limited prin- cipally by the number of available copies. Your Executive Conmiittee is studying this problem and hopes to present a formulated plan to the Association in the near future. Another matter for consideration is that of our constitution. We are operating somewhat loosely by a constitution that was revised and adopted in August, 1930. There are necessary constitutional changes and adjustments to be made before we can function efficiently. A revision is in progress and the Executive Committee plans to present the revised constitution "before the Association at the next annual meeting. In conclusion, we feel that the program this year is one of considerable interest and we hope the sessions will prove to be profitable to each of you assembled here. I want again to extend a hearty and cordial welcome to our members and to those gathered with us at this annual meeting. REPORT OF THE PRESIDENT OF THE O'xBTER GROWERS AM) DEALERS ASSOCIATION OF WORTH AMERICA J. Richards Nelson The F. Mansfield & Sons Co., New Haven, Connecticut The reason for the existence of a trade association is the service it can render to its members. We ar'e the oldest trade association in the fisheries, and the fact that we have been in existence nearly fifty years is evidence that our Association has served its members well. Our basic policy has always been one of maximum service at the lowest possible cost. For the past twenty years o\jr headquarters have been either in Washington, D. C, or Annapolis, Maryland, near enough to the seat of our federal government for close contact with executive and legislative authority. The Increasing importance of business and federal govern- ment relationship diu^ing the past twenty years has made this arrange- ment ideal. Dr. Lewis Radcliff, who served our Association so ably, had an excellent background in his many years of service with the federal govern- ment prior to his coming with the Association in 1932. Mr. David H. Wallace, our present Executive Secretary, came to us from State Fisheries executive work in Maryland. Such backgrounds have given our executives the necessary know-how to deal with state and federal governments in behalf of our members. During the past year your Government Relations Committee, headed by Mr. Joseph B. Glancy, has held several important meetings with the U. S. Public Health Service particularly in relation to the rules govern- ing the breading axid freezing of oysters; also on the very important sub- ject of the service issuing an informative bulletin for the guidance of retail buyers of shell fish. This guide is designed to strengthen the certificate system of the service and is constructive in its approach. Mr. Wallace has continued and expanded our service to teachers, furnishing information for presentation to school children on the life history and food value of the oyster, and other important phases of the industry. He and your President have appeared before congressional committees and have interviewed individual congressmen in behalf of the industry. In addition, Mr. Clancy's committee attended conferences with the Fish and Wildlife Service regarding needed research in the industry and in support of legislation which was successfully passed making available about $3^000,000 in funds from the tariff on fishery imports to biological and technological research in the fisheries. These and other activities are set forth in Mr. Wallace's report. The accomplishments of your Information Committee, headed by Mr. Royal Toner j, were many and varied. You will receive a complete report from him. Oysters have had a good press and are currently enjoying a favorable pulDliCo We are deeply indected to Mr. Toner and Mr. Kessler for their fine work. They deserve our continued support. Our relationship with the National Fisheries Institute is excellent and we have had many instances where joint support of worthy projects by both our Association and N.F.I, have doubtless given re- sults that would not otherwise have been accomplished, 0\ir thanks go to NoF.Io and Mr. Charles Jackson for their fine cooperation. The trade publications hxave, as always, continued to support our Association. Thank you Atlantic Fisherman, Fishing Gazette, and Southern Fisherman, In our efforts to serve the industry, we have not raised our dues for a numJoer of years during the time when the purchasing value of the dollar has been cut at least in two. To some extent it has been possible to overcome this handicap by increased enrollment but that in turn has brought added responsibilities and the work of the Association has naturally increased with the passing years. We have reached a period when a modest increase must be put into effect. Your Directors will consider how this cein best be done and report their con- clusions to you. Certainly such an increase can be kept modest but it is essential, as during the past year we have had to draw upon reserves for operating experxses and such a situation cannot continue. Looking at the future: research designed to increase the industry's production appears to be about the most important project in sight. A great deal of fundamental research has already been done and much of it would seem at first glance to have little relationship to oyster production. However, fundamental research is always basic and in your President's opinion we are on the eve of important develop- ments which are going to put many dollars in the pockets of our mem- bers. Success of the legislation which results in additional revenue to the Fish and Wildlife Service is heartening and if, as a result of this, research can be continued and increased, particularly on the three subjects; (a) predator control, with emphasis on chemical methods, particiilarly in relation to the oyster drill; (b) seed production through better methods of propagation; and (c) the possible development of a hybrid strain that may be much faster growing, easier to propagate, and more resistant to enemies, progress is assured. We have only to look at agriculture to see what has been accomplished with hybrid corn, chemical methods of pest and disease control, and the development of better breeds of animals. ■10» Improved mechanization of oiir industry is progressing largely- through the efforts of the industry itself. We do not offer a suffi- ciently large market to machinery builders for them to develop these machines in their own research programs. Fortunately we have in the industry a number of mechanically minded and ingenious members who have already brought about a minor revolution in the handling of our products. As one example: the planting of oyster shells for cultch, which must be done as rapidly as possible, was but a few short years ago one of our major problems. It was done largely by hand with forks, shovels and wheelbarrows at a season when it was usually excessively hot. Today it is practical.ly completely mechanized; the operation is carried out rapidly and easily and at as low or lower per umit cost as was the case when the dollar purchased at least three times what it does today. We produce a wonderful food. It has excellent consumer acceptance and we can not only maintain our position In the food industry but can and must increase its importance. Wo industry stands still: we must move forward or we are likely to move backward. We have the necessary factors for this advance. Our Association is one of the important cogs in the wheel of progress. Let us use it so that it can serve us to the best of its ability. .11= AMUAL REPOBT OF THE DIRECTOR OF THE OYSTER INSTITUTE AND SECRETARY-TREASURER OF THE OYBIER GROWERS AND DEALERS ASSOCIATION OF NORTH AMERICA David Ho Wallace Bay Ridge, Annapolis, Maryland The functions of a trade association are diversified and some- times quite indefinite. They may vary from a program of development of specific types of accounting for their members, through analysis of business trends, to highly specialized problems of production. The original activities of associations were all too frequently not in the best public interest. This situation res-jlted in a period of general public distrust which is now being gradually dispelled. Even today, people are quite puzzled at my answer when they ask me what kind of work I do. A trade association executive is something which has little meaning for them. Eight out of ten don't know what purpose the trade association serves. Our own concepts have changed. Every such organization is well aware of its public responsibility. The functions have been modified to effectuate this new concept. Efforts are directed constantly to improve our products, production techniques, and distri- bution, so that the oyster - or what have you - can be placed in the hands of the consumer in the best possible condition at the lowest possible cost. A quick look back over the last 30 years in the oyster in- dustry verifies that this program of the Institute has been successful. Oysters have never been produced of a better quality, packed under more sanitary conditions, than is being done today. The consumer is now able to buy oysters with little fear that they are not of the highest quality. This improvement has not come about in a haphazard way. It has been a result of the development of a program started in the late 20's. This is the joint Federal, State, and. Industry program of shell- fish certification. Probably no one single thing has been so important to the industry during the last 30 years as the implimentation of this plan. What is shellfish certification? It signifies that shellfish being delivered to the consumer have been grown and processed under most sanitary conditions. The standard equals that for the milk industry. It means constant checking of all waters by state officials to see that they are pure. It means consistent vigilance on the part of packers to keep their plants in a sanitary condition and finally it means regular checks by the U. S. Public Health Service to determine that state authorities and plant operators are carrying out their part of the pro- gram. The resijlt is shellfish certification. It Is not spectacular - it »12- is Just an ablDreviatlon of a state and a number on each package. But it is a signal to every housewife that she CEUi purchase each such can or package with assiirance. This organization has always supported this program. Our people participated in its inception and have continued to do so through the years. During the past several months the U. S. Public Health Service has "been working to develop a national conference including state health officers, their own shellfish sanitation per- sonnel, and the industry. We have been working with them to develop an agendum. The conference is scheduled for early September in Washington and it will he of great interest to the industry. You are urged to attend. I might point out that shellfish certification is unique in the seafood industry, since it is a voluntary plan. There is no food industry in the country operating under such a system and probably none who have had less sanitation problems. The industry should continue to give this program its wholehearted support. Our organization is also closely interrelated with the activities of the Food ajid Drug Administration. During the past year the Pacific oyster growers applied for modification of their Standards of Identity. The regulations, under which their size categories were established, were outmoded because of changes in processing and marketing conditions. The proposed new size groupings were clear, reasonable and practical. The proposals were presented with supporting data. They were supported by our organization. We presented a united industry to the Administration. The regulations were adopted as proposed. The third federal agency with whom we have had close relation- ships during the past year is the U. S. Fish and Wildlife Service. Your Government Relations Committee has met with the chief of the Branch of Fishery Biology and with the Director to discuss the shellfish research program. Our Board officially requested additional funds for oyster re- search on enemies and spawning and setting studies at their semi-annual meeting in January. President Nelson and I presented this proposal to Mr. John Farley, who gave us a most favorable reception. There is every reason to believe some additional work will be forthcoming on these problems. Furthermore, your Director met with the Branch of Commercial Fisheries to review their program of technological studies. A recom- mendation was made for study of the freezing techniques of southern oysters in an effort to overcome excessive drip. Within the past few days preliminary steps have been taken to effectuate this technological study. These activities with the Service were all in line with the Association's policy to confine its activities generally to the field of research. It appears that this approach should give the best results in increasing production with the least hindrance to the unrestrained operation of the industry. -13- We have not forgotten the role of the States in oyster manage- ment and culture.-. Conservation officials in most of the important States have "been contacted in an effort to promote sound management programs on the public grconds. It is unf ortxmate , 'but ti-^j-e, that public grounds are "being "badly managed in many states. In some the production is only 10 to 20 per cent of what we might expect from the larger acreages and good qijality "bottoms o We have attempted to en= courage the States to improve their culture technique in an effort to increase production. There is every indication that production is the real problem facing the oyster industry at this time. The planters, faced with severe mortalities from enemies, and in some cases from ^unknown causes, and with poor setting, are in a period of low production. The public lands, for various reasons, face the same situation. Most of our efforts have been directed toward development of research programs which might help to solve some of these problems and in the application of knowledge already available to Improve cultural methods. This does not mean that the educational and promotional aspects of the work have been forgotten. I will not go into the public relations and a/ivertising program. You have already heard a discussion of that work. We again advertised our educational pamphlets in the magazine used by High School Home Economics Teachers. The response wag greater than ever before. Over 81,626 pamphlets were distributed to teachers in every State and in various parts of Canada. This was an increase over last year. ■;, The use of these materials has Increased to such a point that one person was engaged in mailing this material for most of the past year. While the cost of the program has thus been greatly increased, we do not believe that the sam.e amount of money could "loe spent more profitably. After all the youth of today will be the oyster consumers of tomorrow. Any method that presents an opportunity to tell about our product, - how it is produced, its excellent nutritive value, and how it can be prepared, - to the teen=age girls and boys must help to interest tlriem in eating oysters. Furthermore, cooking demonstrations are tied in frequently as a part of the program in the schools o This technique of reaching young people has almost unlimited possibilities - the budget is the only check on expansion. For the first time in several years several bills of great interest to the industry have been before Congress. One of them has already been adopted. This is S-2802, introduced by Senators Saltonstall and Kennedy of Massachusetts and others, and its companion bill in the Hous'e by Congressman Bates of this same great Commonwealth, These bills were designed to make available moneys for biological, technological, and ,14= marketing studies collected from imports,. These funds are in addition to those already appropriated o Cur organization supported this legis- lation and President Nelson testified both in the Ho'ose and Senate in favor of the hlllo Its passage and signature ty the President makes $3,000,000 availahle for the next three years. This legislation should enable the Fish and Wildlife Service to carry out the expansion in oyster research mentioned earlier in this talko The other measure in which we have been most interested was the trip-leasing bill which would permit exempt seafood and agricultural truckers to lease their equipment to certificated lines for back hauls. This measure was introduced at the request of the National Fisheries Institute and has passed the House = Apparently because of the strong opposition of certain Senators in the Interstate and Foreign Commerce Committee, it is having a difficult time to move in the Senate » Numerous contacts have been made in support of this bill. These are the type of things your Institute is trying to do for you. We have continued ovx interest in trying to hold down transportation costs for the shipment of seafoods by Express and several of ovtr members have testified in hearings before the ICC. One current problem in this connection is the abolishment of the tariff for Chiorch Containers. An attempt has been made to find a practical substitute for our industry. A conference will be held this afternoon on this subject. Every effort is being made to prevent the Institute from becoming a static organization. Our activities, as you can see, have been diverse. Some of them, such as the work on the Breading and Freezing Shellfish Manuel with the Public Health Service, have been of interest and import- ance to only a few of you. However, we will attempt to keep the members interested in a particular problem advised of our activities so that they will have a chance to present their position and explain their needs. Our program is dynamic. It is flexible to meet the needs of our industry. Do not hesitate to avail yourself of its varied services. In the meantime, we will be alert to discover any development which might be detrimental to the industry and to handle it promptly. •15- SYMPOSIUM ON VAEIOUS ASPECTS OF OYSTER SETTING The following seven papers constitute a special symposiiim on problems related to setting of oysters in states along the east and gulf coasts of the United States,, OYSTER SETTING J. Richards Nelson The Fo Mansfield & Sons COo, New Haven^, Connecticut A dependable source of seed is of coixrse a fundamental component of a successful oyster growing business. In the southern areas of our coast, from Virginia south, it at least appears to us who are engaged in oyster growing in the Long Island Sound area, that the obtaining of a set is not too difficult o Certainly it is a major problem in our area and one which has been the subject of considerable investigation during the past fifty years o There is a good deal of information that has come out of these investigations which we can use profitably. However, there is a tendency by the oyster grower to oversimplify the problem and to feel that perhaps some one factor such as temperature or rainfall is dommaxit. We have so many instances of seemingly favorable temperature and rainfall conditions during the spawning season with no good setting results, that we can draw the conclusion that many other factors enter into the problem. It is undoubtedly quite complex and I picture it as a number of factors represented as teeth on a gear-wheel where each in turn must mesh with the teeth on another gear in order to function. If one or more of these factors is missing, the rest may be present without a good set resiilting. Let us examine the factors that we know about' fresh water seems to be important, as the industry has historically obtained its set from areas where fresh water from the land joins with the high salinity water in the Sound. Yet we know of several examples where extremely heavy sets occur with fair regularity in areas where there isn't a great deal of fresh water. Specifically I refer to the ocean side of Virginia and to the Cape May shore of Delaware Bay. In both of these areas setting occurs where the tide ebbs out completely, or nearly so, exposing the set to the air. Fresh water is certainly important in the control of predators and I wonder if perhaps that is not its most importajit function, granting of course that there must be some reduction in salinity below that of ocean water. The natural beds of Delaware Bay lie in an area where drills cannot normally thrive. It appears to me that the most successful seed -16- plantings made in the lower bay or cove are those from seed that has spent at least two years on the natural beds, with the result that they have sufficiently heavy shells to better withstand the attacks of drills, crabs, fish, and other predators a The recent transplanting of set from Lower Delaware Bay to the natural beds should give some highly interesting data on this subject. In addition to a source of fresh water and a shallow axea location, we must of eoiorse have sufficient parent oysters. Evidence in Connecticut would indicate that natural oysters growing in rivers and creeks may be a most important source of lar-vae for setting in areas where these rivers and creeks meet the Sound. Depletion of so many of these nat-aral beds is certainly a matter of grave concern. The question of clean cultch is one factor that we can be reasonably sure of although at times there has been evidence of seemingly clean cultch missing a set where shells that were seemingly fouled obtained one. I wonder if one of the factors that is present in shallow areas where the setting takes place between tidal zones isn't this question of clean cultch? Wave action tends to keep the cultch clean and the effect of the s\m at low tide is probably also a factor. Here again, such a conclusion may be an over-simplification of the problem. What can we oyster planters ^ operating in the Long Island Sound area, do to assure ourselves of a set with sufficient frequency to keep our business healthy? I think there is quite a lot that we can do with the knowledge that is already available and these are the steps that I believe should be taken: (l) Concentrate shell plantings in the areas where best results have indicated a larger percentsige of sets, and particularly in such areas that are near a source of brackish water in which oysters set naturally. If the natural set has been removed, supply spawners even if this has to be done at the risk of their even- tually being stolen. (2) Prepare the cultch to be planted so that it is as clean as possible and time the planting of this as close to the date of expected setting as possible. Adult oysters present on the setting bed, even though they are only scattered, appear to be important in the light of the findings of Dr. T. C. Nelson, regarding the possibility of their acting as larval collectors. (3) Predator control is essential and it is my opinion that we obtain a set of oysters of commercial intensity in many seasons that are later termed failures. I believe that newly hatched drills kill this set before we even see it. The results which Mr. Glancy has ob- tained in Peconic Bay where he has an arrangement for trapping oyster larvae in shell bags and keeping out the drills, is a case in point. He has obtained a commercial set in areas where this was not believed -17- possible. I am firmly convinced that the suction dredge is the best method that has yet been devised for combatting drills and, under some conditions, star fish. I further believe that with the application of the knowledge we have, we can produce a commercial set in some parts of the Long Island Sound area on an average of three years out of five; and that if we do an adequate job in fighting predators, this can supply us with the seed we need. I do not wish to convey the impression, however, that we don't need more research, as we most certainly dOo Artificial propagation of oysters appeared to be a solution to the seed problem more than fifty years ago but this has not proven to be the case. However, the outstanding results obtained at the Milford Laboratory of the U. So Fish and Wildlife Service, indicate that this still is a possibility and undoubtedly is a logical method of trying to produce a hybrid oyster which is faster growing and resistant to enemies and other causes of mortality. I would not for a moment dis- card the idea that artificial propagation may eventually solve the oysterman's seed problems but I believe it is some years away. In the meantime we will have to proceed with the knowledge we already have. I have every confidence that the scientists who are working on this subject and of whom many are present at this meeting, will in the next few years make some important discoveries that will result in the solving of the seed oyster problem for all time. =18- HOW TO INCREASE PRODUCTION OF SEED OUTERS IN CONNECTICUT V. L= Locsanoff Uo S. Fish and Wildlife Service, Milford, Conn. The study of the time and intensity of oyster setting in Long Island Soiind in relation to environmental factors has been one of my chief interests for over 20 years. On several occasions I have had the opportunity of discussing the results of my observations at these conventions, the last being in 19^8 when I offered my conclusions based on observations of 12 years covering the period from 1937 to 19^8. Since that time, we have added several more years of field observations and have also substantially broadened our knowledge of larvae by studying their behavior imder controlled laboratory con- ditions o Regardless of the additional material accumulated diH-ing the last few years our basic opinion about larvae remains more or less the same as that expressed in 19^+9 ■> In other words, we think that the oyster larva is a hardy organism and that it can withstand numer- ous, often quite radical changes in its environment without perish- ing. We are also quite certain that the intensity of setting of oysters in Long Island Sound is not to any appreciable degree cor- related with slight changes in envijrcnment which in the past we regarded as extremely important. Among these factors, considered singly and in groups, were temperature, salinity, hydrogen=ion concentrations, solar radiation, precipitation within a water-shed affecting Long Island So\ind, and the amount of spawn developed by oysters prior to the beginning of the spawning season. We have also made rather extensive studies of the direction and velocity of the wind, but so far have found no correlation indicating that they re- flect upon the intensity of setting. On the other hand, our laboratory studies of larval behavior, especially their food requirements, some of which have already been reported at this convention by my associate, Harry C. Davis, and by me have shown that oyster larvae, unlike those of many other bivalves, are unable to survive on most planktonic forms fed. to them. This leads us to believe that perhaps in natiire oyster larvae may have difficiilty in finding nannoplankton that they can take in and assimi- late. The relative absence of such forms in some years or in certain areas, or the difference in their numbers, may "be responsible for fluctuations in the intensity of oyster setting from year to year. As already pointed out in some of my articles, the years of good oyster sets in Connecticut waters are quite uncommon. I base this conclusion on the records of the State shellfish authorities. ^9' information which was kindly supplied to me by oyster companies which have been operating since "before the turn of the century and, finally, from my own observations which cover almost a quarter of a century. For example, these records show that between 1904 and 1925^ a period of 21 years, not a single general, heavy set occurred in the Sound, During this period the industry survived by buying abundant seed oysters that grew on so=called natural beds which were located mostly in shallow inshore waters » Since 1925^ we have had good sets only on five occasions, i.eo, 1930, 1939, 19^^-0, I94U and 19^15., In other words, in the last ^k years we have had only six or perhaps seven good, general sets. The remaining years were either complete blanks or so-called marginal yearsy ioeo, years during which a general, light set occurred in the Sound, or when good sets occiirred in bome sections but in other areas setting was a failure, as happened in 1953^ when only the Bridgeport area caught a good set. Let us imagine a farmer vfho would gather a commercially pro- fitable crop only every eighth or ninth year. How long could he con= tinue to exist? Should he not look for other tracts of land where more regular and more abundant crops could be grown? I think he should and I also think that the Connecticut oyster industry, imitating a wise farmer, shoiold also consider the possibility of transferring a sub- stantial portion of its seed oyster production operations from the open Sound to more promising areas. Please notice that I do not advo- cate a complete change, i.e,, abandonment of the oyster beds in Long Island Sound proper, I merely suggest the extension of our oyster cultivating efforts into shallow, more protected waters where conditions for production of seed are more promising. Let us begin to discuss the necessity of this move by admitting that most of the conditions affecting the oyster industry of the Sound proper are virtually uncontrollable „ These conditions may be either of physical or biological, natijire. The most outstanding examples of the former are our highly destructive storms = The industry still re- members that of November, 1950, which killed millions of oysters, rained many beds and placed several oyster companies on the verge of bankruptcy. Nothing coiiid have Been done to prevent this catastrophe because the stona came without watrning. Of the biological factors we would probably think, first of all, of such well known enemies as starfish and drills. It is true that they may be eliminated from small areas by the persistent use of lime, mops or suction aredges, but they will continue to invade the beds from the surrounding grotmds which remain uncleaned. Furthermore, as is well known, star-fish have pelagic larvae, which are carried around by the currents and which may set in immense numbers on an oyster bed regardless of how free of adult starfish the bed is. We know many cases of this nature. We may also mention several formerly extremely productive oyeter setting areas which were eventually given up because it became economically unprofitable to defend these beds against the enemies. -20- Thus, it is clear that the open Sound is not only an unreliable place for getting sets regularly tut also a place where if the set does occur, it remains difficult ajid expensive to protect against enemies. The question that naturally arises tecause of these con= siderations is what the industry could or should do to place itself in a more advantageous situationo The answer may "be that a partial solution of this problem should consist in the utilization of numerous bays, harbors, ajid deltas of rivers where extensive natural beds of oysters existed in the past, but which at present are barren and use- less. What are the advantages of gravitating towards irshore areas? There are several important ones. To begin with, oxa- observations, as well as those of our predecessors in biological phenomena, show rather clearly that oyster set rarely fails in inshore waters. We estimate, for example, that in Milford Harbor and Indian River, if they were properly planted and managed^, a set of commercial importance could be gotten nine out of every ten years. Furthermore, beds located in bays and harbors would be better protected against storms. Finally, because the salinity of the water in many inshore areas where oyster beds could be established is comparatively low, the oysters, especially young set, would be protected by nature itself against starfish and drills, which require a comparatively high salinity to exist and propagate. This consideration alone is of tremendous practical significance because it eliminates from the debit side of the companies' ledgers astonishingly high sums of money spent on pest control. A criticism of our suggestion may be offered by pointing out that most of the inshore waters are more heavily polluted, industrially and domestically, than Long Island Sound proper. This should be ad= mitted, but since the Connecticut industry is chiefly concerned with seed oysters which will not be sold for several years, the matter of sanitation does not enter into the picture. Ftirthermore, our observa- tions indicate that, as far as tolerance to domestic and industrial pollution is concerned, oyster larvae and young set may be hardy organisms. I base this conclusion on observations familiar to all of us from Connecticut that heavy sets have often occurred in the Quinnipiac River in New Haven, Poquonock River, Bridgeport, and Housatonic River, which drain the most heavily industrialized areas of our State. We may also recall that during 19^^, when all our industries were at their maximum production for the war effort, and when due to the inflow of hiindreds of thousands of industrial workers the problem of domestic pollution became rather acute, we had one of the best oyster sets since I9OO. Yet, we have to admit that during this year there was more pollution entering our waters than normally. This, of course, does not indicate that pollution is desirable or harmless to oyster larvae. It simply shows that larvae possess quite a tolerance and, therefore, rivers which are slightly polluted should be considered among the areas capable of procuring heavy sets. Furthermore, if the =21= trend toward abatement of pollution developing so well during the past 25 years shoiild persist, and we have reason to believe it will, pol- lution may not te a problem at alio The chief obstacles to the utilization of natur-al oyster pro- ducing bottoms are, in my opinion, the archaic regulations many of which were passed more than a century ago, and which designated most of the inshore waters as public grounds. In other words, those areas cannot be rented to private individuals or companies for cultivation of shellfish. These regulations, which in the past perhaps were desirable, have eventually led to the present condition where we find the majority of our potentially most productive oyster areas virtually baxren due to lack of care. Thus, from economical and biological points of view these areas are now entirely wasted- Since there is practically no one making a living fromrt.hese areas, logically, no one would suffer if some of these beds were leased for cultivation to private individuals or companies- By proper cultivation of these areas the industry would become assured of an abimdant annual supply of oysters, and the township in the State would gain additional revenue. In connection with this discussion we should add that utiliza- tion of numero\is shallow salt water ponds should also constitute part of the program which I suggest. Some of the ponds in Martha's Vineyard have proven quite productive and the studies which we initiated with the help of some Connecticut oyster companies along the same line suggest that such ponds may eventually be utilized not only for the production of seed oysters but also clams. Several technical problems will have to be met in connection with moving some of the industry' s activities into shallow inshore waters because the methods to be employed there would necessarily differ from those Vtsed in the open Sound, I am siire such problems would be rapidly solved by o-ur oj^stermen who have been capable of designing and placing in operation such complicated mechanical devices as the suction dredges now operating in the Sound. '22" OBSERVATIONS OF THE BEHAVIOR AMD DISTRIBUTION OF OYSTER LARVAE Thurlow Co Nelson Department of Zoology, Rutgers University, New Brunswick, New Jersey I. Brief Resume of Spawning and Larval Development « In common with other sedentary marine animals the oyster secures distribution of its species through a pelagic or free swimming larva. Since the brackish water zone most favorable to the oyster's existence is rather sharply limited^ it follows that within the 60 odd million years during which our oyster has existed on this earth its young stages have developed reactions which bring enough of them back into this limited zone at the end of their free existence to maintain the species. To the biologist this means that selection has favored the perpetuation of those laxvae which behaved in such a manner as to return them close to, or upstream of, the ancestral home from which they departed two weeks earlier. To the practical oyster grower it means getting his shells overboard at the right place and as close as possible to the time of setting in order to avoid excessive foxiling of the shells with other organisms. With definite limits on equipment and man power available for planting often many thousands of bushels of shells, the grower is usually forced to ignore the dangers of fouling, trusting that some portion of the majority of his shells will be clean enough to catch at least a few spat. The American oyster grower is quite aware of the losses he suffers through fouling of shells and woiold certainly welcome economically practicable means of reducing or avoiding this. On demonstration are two shells from wire baskets placed on the Cape May flats of Delaware Bay a month ago. The densely set shell, one of thousands equally clean and heavily set was ou a bar exposed up to four hours of hot sun during the spring tide period. The other bearing only an occasional spat is typical of all the shells from wire bags dropped in an adjacent slough where they were continuously under water. Korringa has been quite successfiol in Holland through the use of D.D.T. in preventing the attachment of two of the most objectionable fouling organisms in his area, barnacles and hydroids. Cement covered roofing tiles used to collect spat by the Dutch oyster growers are given a bath in D.D.T. emulsion with oil and water in such concentration that each tile bears approximately I5 milligrams of D.D.T. when planted. Translated into more easily understood terms this means approximately an ounce of D.D.T. to I9OO roofing tiles, an amount which apparently is not toxic to oysters. -23- British investigators at the Fisheries Experiment Station at Burnham-on-Crouch, however, report little success with DoDoT„ The recently imported New Zealand barnacle has rendered their coated egg crate partitions worthless for catching oyster spat after as short a time as 48 hours o Science rendered its first assistance to the oyster grower in solving this problem through determining from microscopic examination of the water for larvae when spaiAming begins. To our knowledge the first such declaration was made to the oyster growers of Barnegat in 1908 by Dro Julius Welsono At that time he believed the length of larval life to be approximately three weeks o Meanwhile in I9IO Dr.. Joseph Stafford had published two important papers on the "Larva and Spat of the Canadian Oyster" wherein the foot and the eyespot of the mature larva were first demonstrated in drawings. By 1915 the length of the larval period in New Jersey was shown to be two weeks, and based on this information the first pre- diction to oyster growers of the time of expected set was made in Little Egg Harbor, New Jersey, in 1916, The prediction made 10 days in advance was fulfilled with an error of but 2k hotirSo During the decade following the close of the first World War-, Churchill and Outsell in Great South Day, Prytherch at Milford, Connecticut, and our- own staff in New Jersey placed prediction of spawning and setting of oysters on a thoroughly scientific basis. In Barnegat Bay with its single population of oysters engaging in mass spawnings it was possible to predict from the temperatuire curve when spawning had occurred. The reliability of predicted setting in this area is dramatically illustrated by the following incident. Shells were ordered from Cris- field in 192U on the basis of the prediction but word of their deflec- tion to Bivalve because of storm damage to the boat was received July 3rd,. Lear-ning that the set due on the 7th would be heavy the planter contacted the Jc& Jc¥, Elsworth firm at Greenport by telephone and was promised that a boat would be loaded with shells and started for Barnegat by tlie evening of the 5th. The boat entered through Barnegat Inlet on noon of the 7"bh, and being informed of the presence of large niMjers of eyed larvae in the water, the crew worked till midnight un- loading the shells. Next morning the shells examined averaged appro- ximately 60 spat per shell distributed on both upper and lower surfaces. Fortified with such experiences your speaker boldly published in 1928 his conclusions that 68°F or 20°C. was the critical temperat\are for spawning with actual spawning occurring at a somewhat higher tem- perature depending upon the rapidity of rise of temperature above the critical point. Subsequently, however, Loosanoff and Engle working in Long Island Sound found spawning at 62.5°F-^ while in the Gulf A. E. -24- Hopkins foijnd spavning only subsequent to temperatures of 77°Fo Our own observations in Delaware Bay had in the meantime revealed that the Barnegat Bay formula just did not work when applied to the much larger and more diverse Delaware Bay. Finally Dr. Leslie A. Stauber in a masterly analysis of the da,ta. from Long Island So^ond^ Prince Edward Islajid, Canada, and Delaware Bay demonstrated that three physiological races of oysters occur along the esLStern Atlantic Coast with critical temperatures for spawning at 15, 20, and 25° C, or 59, 68, 77° F. Actual temperat^jres at time of spawning are usually 3-^ degrees above the latter range since tempera- tures continue to rise while the final biological processes necessary for spawning are completed. Thus far Dr. Loosanoff with his definite formula for date of first spawning in Long Island Sound has come up with the most reliable data for use of the oyster grower. Although temperatijire appears to be the most important factor in the environment inducing spawning, it is certainly not the only one. Dr. Philip A. Butler of the Fish and Wildlife Service Laboratory at Pensacola informed me only last May that water temperatures adequate to produce spawning may prevail for one to two months before spawning begins at Pensacola. Here the necessary factor appears to be the spring bloom of algae which furnishes the food and possibly other important sub- stances such as vitamins necessary for the production and the elimination of spawn. It is fascinating to speculate on the possibility that one of the vitamins such as vitamin E or K involved in reproduction in higher animals is f-'jirnished by some of the algae in that part of the Gulf during the spring bloom. As the above was written I received Dr. Loosanoff 's Bulletin #6 dated July 23 which reveals that Long Island Sound oysters were also as of that date waiting for some stimulus other than high temperature. Was some vital food organism, formerly present, absent or in small numbers this year? Further bulletins from Milford are impatiently and eagerly anticipated. II. On the Effects of Salinity Gradients and Currents In Determining the Distribution of Oyster Larvae. The velum or swimming organ of the oyster larva while sufficient- ly powerful to enable the little animal to ascent slowly from the bottom to the surface is quite incapable of swimming against even a feeble tidal current. The larva, therefore, unless resting actually on or in the bottom is at the mercy of currents whether produced by tide or wind. In our survey of oyster larvae in Little Egg Harbor in I916, published in 1917, twelve stations were established. Most of the parent oysters lay from a half mile to a mile toward the inlet from the location of the laboratory house-boat at Edge Cove, with but small numbers in the upper half of the bay where bottoms were much too soft for planting. Star-ting at Station 1 at the mouth of Edge Cove and proceeding along the shore and away from the inlet the total numbers of larvae taken -25- over a period of 12 days at each station were as foUovs ; Station 1 (Edge Cove) . = . _ _ 2,900 3 = « - „ _ 3,600 k . ^ •=. . = U,o82 5 - = - - - U,i09 6 (Parker Run) - . = _ . 6,700 9 . . = _ - 521 These figures show a progressive increase in nuinbers of larvae as we pr-oceed up the tay and upstream from the parent oysters » We know, however, that there is a steady movement of water seaward through which land drainage and stream discharge are carried cut into the oceanu How then are oyster larvae though unable to stem even a slight cixrrent able to avoid, dtiring their two weeks' floating life, being swept out to sea? Samples taken from a "boat anchored in the inlet showed oyster larvae in small numbers passing out to sea with the last of ebib tide but almost equal numbers retur-ned with the early flood, thus emphasizing the tendency of tidsil masses of water to remain essentially intact. The numbers of larvae, however, were insignificant showing that some other factor must account for holding the majority of the larvae near the head of the bay. Subsequent observations during the nineteen twenties in Bernegat Bay revealed that the early or straight hinge larvae were indeed carried as much as one to two miles seaward but that by the close of the first week of their free existence they began working back toward the oyster beds from which they cameo Most of the larvae by the setting period a week later reached a point well upstream from their place of births The Barnegat Bay studies also revealed for the first time the behavior of bivalve larvae in relation to salinity gradients and currents. This bay with essentially level bottom between 2-2|- yards deep and with tidal fluctuations between h-6 inches and relatively feeble currents shows but little turbulence.-. During quiet weather marked stratification occurs with highly saline water from approximately mid depth to the bottom, overlain by water of much lower salinitya At times greater in- crease in salinity was observed, through lowering the hose intake 8 inches than in running the boat k miles closer to the Inlet » The transi- tion zone between low and high salinity water masses is quite sharp and is designated the halicline. Let us examine two of the more extreme cases of salinity stratification in Barnegat Bay taken from the 1931 bilLletin by E. B. Perkins and the speaker. In figure 25 of this bulletin it will be noted that the salt content of the water was doubled in descending approximately 8 inches » This study was made on May 23 when no oyster lajrvae were presents However soft clam larvae were abundant with k^O per sample of 100 liters, approximately 100 quarts, at the ■ top of the halicllne and 8U at the lower siu-face of the halicline- All of these were Immature » In the sample taken from close to the bottom =26= were ^550 mature clam larvae ready to seto In contrast to its effect on distribution of oyster lar^vae this sharp increase in salinity offered no "barrier to mature clam larvae which passed through the salty zone and down to the "bottomo Figure 2? taken on June 23 shows the effect of the halicline on dis- tribution of oyster larvae with 126o per sample at the top of the halicline, but orJ.y 68 per sample in the high salinity water within 8 inches of the bottomo Note in figui-e 28 66,110 larvae at the top of the halicline but only 102 dovm close to the bottom in the highly saline water o By contrast, with xmiform salinity from top to bottom shown in figure 31 the differences between numbers of larvae at sur- face (2630), mid-depth (2620), and bottom (250O) are well within the limits of error in sampling and in counting the larvae. A complete series with samples drawn at successive 8 inch levels (0.2 meter) is shown in figure 23 » The larvae increase in nimibers per 100 liters from 4,050, 8 inches below the surface, to 35,710 at the top of the halicline and 20,000 at the lower surface of the halicline from whence the highly saline water with slight increases continues to the bottom. In all, some 32 figures are given of observations by the speaker in this report all showing concentration of oyster larvae where sharp in- creases in salinity occur, and no such concentrations of larvae in uniform salinity or nearly soo Because of the necessity of smooth water for working in such narrow limits all observations were made in the early morning before the wind arose. Subsequently Dr. Perkins and assistant Vincent 0. Lesh conducted their studies during the next two years at the same locations using a large scow kindly provided by the Jo & J„ W. Elsworth Company^ Sampling, larval countS;, and salinity detenninations were made on board since moderate wave action did not cause undue motion of the scow. As a result Dr. Perkins demonstrated that wind blown currents can be as important as salinity gradients in determining the verticsd. distribution of oyster larvae. His observations fjrst reported in our joint 1931 bulletin apparently did not confirm our earlier observations on salinity effects, but in 1932 following further observations Dr. Perkins concluded as follows: (Ann. Rept., K. J.Agr.Expt.Sta. for 1931, p. 121-122): "Summary of Observations on Vertical Distribution of Oyster Larvae" "Oyster larvae are distributed vertically in the waters of Barnegat Bay: (a) by their own activity in responding to salinity changes, (b) by the action of tidal and wind blown currents which sweep them into the level or levels of increased current velocity; and (c) by a combination of these forces." "With formation of the halicline the laj:°vae react by swimming -27- above the more saline water into the lower levels of the overlying fresher water provided current velocities ax-e low." "When ciH'rent velocities are high, even though the halicline he present, the larvae shov increased concentrations at levels of greatest current velocities J' "When no halicline is present, as when salinities are con- stant from surface to 'bottom, or when there is a gr'adual decrease in salinity without a sharp break at any level, the larvae are con- centrated by the current at its level of greatest velocity^ VThen the current is negligible, under these conditions the larvae are found in gr'eatest n'uiabers on the hottom." Experiments made in the laboratory w,ith mature oyster larvae freshly caught hy tow net in Delaware Bay show that raising the salinity of inflowing water increases the n-umber of larvae actively swimming while decreasing salinities result in inactivity of the majority^ With no change in salinity an increase in current velocity is followed hy prompt increase in swimming activity. This observation is in direct opposition to the findings of Dr., Prytherch in Milford Harbor. There according to him the larvae swim only during slack water, remaining for the rest of the time on the bottom^ Although the above story may sound complicated, later researclvss by ourselves and others have shown that we were lucky indeed to have begun our studies in Baxnegat Bay^ The pict\ire there as regards spawn- ing and lajr/al distribution is simple compaor-ed with Delaware Bay and probably Chesapeake Bay and other large estuaries » Bamegat Bay with its level bottom and slow currents shows very little turbulence, whereas in Delaware Bay water which at one point is close to the bottom may meet an obstruction and be shot up to the surface a few yards awayo Finally let me quote from our 1921 Bulletin in which it is shown how the early larvae are swept do^fn the Bay to return by successive steps upstream. By settling close to or on the bottom during slack water the older larvae in particular get into the lowest stratum of water, one which we now know in Delaware Bay runs approximately an hour longer on the flood than on the ebb„ Dr^ Pritchard and co=workers on the York River, Va^ , have in recent years shown how this net upstream tidaJ. move- ment can transport oyster larvae away from the sea and back toward, or even above, their ancestral homeo =28- VARIOUS ASPECTS OF O'fSTER SETTING IN MARYLAND ^ G. Francis Beaven Maryland Department of Research and Education, Solomons, Mai-yland As in most oyster producing states, Maryland presents a VEiried pattern of oyster setting « Production over much of its area is limited by available supplies of seed -which remain far below the quantities needed. Consequently the problem of securing increased sets is one of major importance to the industry. D^oring recent years much study has been directed towards gaining a more complete and accurate knowledge of the existing setting pattern throughout the State, and towards indicating methods for improving the effectiveness of shells planted as cultcho The many diverse oyster beds of the State may be grouped roughly into three general classifications according to their general setting behavior. The most extensive group consists of those bars capable of producing a good growth of high quality market oysters but upon which the average rate of recruitment is too low to replace the adult oysters removed by normal harvesting practices. Many such bars at present either are entirely nonproductive or seriously depleted. They can be returned to and maintained at a high level of production only through continued plantings of seed oysters upon them as successive crops of mature oysters axe removed. A second classification comprises certain limited areas of self-sustaining bars where the average annual set is sufficient to replace the oysters removed when harvesting is limited to relatively inefficient gear such as hand tongs. Most of Maryland's present natural yield comes from such areas. The third and least ex- tensive type consists of those bars that frequently receive sets which are too crowded to yield satisfactory crops of market oysters but which are of great potential value as sources of seed. Several such areas have been set aside by the State for seed production but many still are worked only for the meager crops of slow growing oysters that survive to reach market size. Maryland's Chesapeake area differs from many oyster producing regions in the relatively low but comparatively stable salinity of most of its waters, and in the lack of even occasional rises to salinity levels approaching those of the open sea. Most oyster beds lie in water averaging less than 15 parts of salt per thousand. The lower portion of Tangier Sound on the eastern side of the Bay exceeds this f igiire only slightly but is sufficiently salty to harbor both species of the screw borer or oyster drill. Chincoteague Bay, lying along the Coast, is of high salinity and supports a small private oyster industry whose principal outlet is the raw bar trade. ^Resource Study Report No. 7. Chesa. Biol. Lab., Md. Dept . of Research and Education, Solomons, Md. »29- Some fifteen years of irregular records of spat fall upon natiiral cultch reveal a faii'ly consistent pattern of setting when data are grouped by large general areas o Figure 1 presents a twelve year average of spat fall in representative areas » The rate of sett= ing shows a gradual increase from the upper limit of oyster growth down to the Virginia line- There is a smilar increase from the upper towards the lower part of those tri'butary rivers which contribute a fairly large stream fl'3W and whose upper tidal reaches are fresh. Conversely, in the many small estuaries of the Bay which possess little or no draina,ge basins and hence show little salinity gradient, settiiig typically is heavier in their upper reaches than near their mouths o The eastern side of the Bay exhibits a distinctly higher setting pattern than the western side and, typical of the physical nature of estuaries on the northern hemisphere, possesses a somewhat higher salinity and greater tidal amplitude than occur at points along the opposite shore » Marked variations in setting are common from bar to bar and from one part of a given bsir to another within the general areas from which this overall pattern of setting is drawn^ Oyster setting in Maryland may begin in late May and extend well into October « Usually a marked -peek in setting of about two week's duration occurs at some time from late June to September, typically during July in most areas. At a few locations, however, the principal set often occurs in the fall. Different areas may show characteristic patterns differing from one another and differin^j from season to season at the same locationo Figure 2 shows the 1953 setting pattern for several areas in the southern part of the State, In some instances t^/o or more distinct peaks of setting appear. Test shells for these observations usually were exposed on the bottom in depths of water varying from 3 to 20 feet. Setting typically is better along the shallow or inshore margin of a bar than along its deeper portioriS. Intertidal setting occurs to a very limited extent along the margins of certain small estuaries where the shore line is not subjected to shifting by v&ve action. In an effort to make more effective use of planted cultch, observations that indicate the most favorable setting areas and those that show the effects of improved timing of plantings have both proven of practical use. By eliminating shell planting efforts in many of those areas that have demonstrated a long and consistent record of little or no spat=fall, the average annual set upon State planted shells has shown a marked improvement. Further concentration of shell plantings upon areas with good setting records should make possible even better returns than in the pasto Improvement in the timing of shell plantings in Maryland waters presents a much more difficul.t problem than that of locating shell plantings upon areas with good setting records. Examinations of oyster gonads indicate that oysters in tributary and shallow waters usually are =30- IS YEAR AVERAGE SET ON NATURAL CULTCH BY AREA 1942 . I9SS Fig. 1. Distribution of natural oyster set in the Maryland portion of the Chesapeake area. 51 OYSTER SLT ON TEST SHELLS > < a cr UJ a. o < u. UJ X CO cr Q. < Q. JUNE I . I I t I I I I SMITH CREEK ST. MARYS RIVER HOLLAND STRAITS PUNCH IS. OR UPPER HONGA R. AUGUST septem"be!r| ocToekf^ 1953 Fig. 2. Season and relative abundance of spat-fall in several Maryland areas . 32 the first to spawn while those in deep or open water may spawn much later. Many of the scattered oysters on the deep bars of the open bay or large tributaries have been found to retain most of their ripe sexual products through the end of the spawning season. The many factors which resiilt in widespread variation of the time and intensity of spawning make it difficult to devise a formula for predicting the occurrence of peak oyster setting such as has been successfully done in certain other areas. Limited observations of larval abundance taken over fairly wide areas by means of a high speed plankton sampler offer some promise as a means of predicting a wave of setting about a week ahead of time. Such short notice is not of great practical value in timing large scale shell planting operations and may not always prove reliable due to the almost com- plete loss of large groups of larvae which have at times been observed. A further limitation upon this method of forecasting lies in the ex- tensive sampling that would be needed to cover the many diverse areas within the State. The degree of fouling of commercial cultch has a major effect upon its efficiency as a spat collector at the time when an oyster set occiirs. In the mid-Chesapeake area a heavy wave of barnacle set usually appears during late spring and again in late fall. Shells which are planted after the late spring barnacle peak have demonstrated a much higher oyster set than those planted at the same location prior to or during the barnacle set. Rather surprisingly, however, at several locations where tests were made, shells planted several months ahead of the barnacle set have shown higher catches of oyster spat than those planted a few weeks before or diiring the spring peak of barnacle set- ting. This resiilt appears to have been due to an accumulation of organic film or slime which makes the older shells less attractive to barnacles but does not interfere materially with oyster setting. A similar type of ecological succession resiilts in the set of Bryozoa, a major factor in fouling during late summer, becoming much heavier upon newly planted shells than upon older or seasoned shells. Bryozoa in the Solomons area during late summer can completely cover newly planted shells in less than three weeks so that a planting made that much ahead of a late summer peak of oyster setting may, under such conditions, be almost useless as cultch. The fact that our limited areas of high oyster set are comparatively free from heavy growths of Bryozoa and barnacles is believed to be one of the factors that makes them more favorable for production of spat. Many data upon the time and intensity of oyster setting and of the set of fouling organisms have been accumulated over a period of years through the use of clean test shells at certain locations. These have revealed characteristic patterns which offer a usef^ol guide for the timing of shell plantings in those specific areas. The marked differences in the time of barnacle sets and of peak oyster setting =33" which have feeen found' LluTca^ scaTtereB. observations at other locations make it improbatle^ however^ that these same patterns can he laroadly appliedo More extensive information of this type is needed. Some of the local factors which affect the intensity of oyster setting are readily apparent "but the causes of many marked fluctua- tions which occur are not yet clear. The physical factors governing water circulation in the Bay embodying the effects of Corioli's force offer a ready explanation for the greater concentration of oyster larvae along its eastern side with res;ilting ?iigher sets there. The presence of larger quantities of trood stock in the more numerous eastern shore trilautaries also increases the setting potential of that area. Oysters in the upper portion of the Bay and of the larger rivers are subjected to low salinities which at times may be mai'ginal or even lethal o Both Dr« Loosanoff aj^d Dr, Butler have shown the extent to which low salinity may reduce effective development of oyster gonads,. In years of excessive fresh water run-off low salinity conditions often prevail for long periods and undoubtedly are the direct cause of sojoe of the fail\ires in oyster setting on such up-stream beds. Although conclusive evidence is lacking, several plausible hypotheses offer f\irther explanation of some of the observed variations in oyster setting in the Maryland areao Two distinct types of high setting areas appear to be present. One type occurs where rich rvin.- off enters directly into high salinity waters producing a body of water exhibiting a fairly steep salinity gradient. Oyster beds in such areas are subject for brief periods to salinities low enough to prevent the establishment of many of the predators and fouJ.ing agents that hinder spat survival in waters of a more su£ts.ined high salinity,. Typically the lowest salinities prevail dui'lng spring and higher salinities are usual in summer and fallo The combination of periods of high salinity and fertile water seems to be favorable to the production and growth of 03'"ster larvae. A steep salinity gradient also produces a pattern of circ-ulation tending to concentrate the larvae within the stream and the comparatively clean cultch favors successfvil setting. Unfortunately such areas are quite uncoramon in, Maryland due to the generally low and flat gradient of upper bay salinities. In the southern portion of the State a few wealcly defined areas of this t3y"pe do. however, appear to produce somewhat better sets than elsewhere o A second type of high setting area consists of a semi enclosed body of water where the salinitjr is fairly uniform and where there is a comparatively slow rate of exchange of water overlying the oyster beds. Oyster brood stock is fairly abimdant and usually occurs in rather densely populated groups. Water circulation is such that swarms of larvae are not dispersed through large water masses and so remain rather concentrated over the beds . Such areas s-re fairly common. ,3!^^ SPAT PER BUSHEL OF OYSTER SHELL ON PLANTINGS MADE AT DIFFERENT DATES bJ X (/) K bJ K > o u. o Ul z UJ a. < a. 600 - 500 400 - 200 - 10 0- 30 - 19 5 2 19 5 3 DATE OF PLANTING OF EXPERIMENTAL SHELLS Fig. 3. Variations in commercial (November) set upon shells planted at different dates in the same areas. 35 especially "behind or between islands and in certain sluggish tributaries. Presently designated State seed oeds are mostly m areas of this type. Quite marked variations in setting occur in all areas from year to year which are difficult to explain Attempts have Deen made to correlate them with temperature, precipitation, salatu ..y, prevailing winds and other factors o It is "believed that the presence or absence of organisms suitable for oyster larvae to feed upon may be a critical factor. "Variations in plankton "bloom are difficult to explain but Mr. James B. Engle has been gathering data in the Eastern Bay area which indicate fhat the atundarice of nutrients contri'Duted by stream flow, when not accompanied by salinities low enough to retard gonad develop- ment, may be an important factor in producing the conditions needed for satisfactory sets a Accurate records of setting in Maryland are not available over a long period of years.. Statements made by Dr^ Brooks, Dr^ Graves, and others concerning the abundarxe of spat during the latter part of the past centiury indicate strongly, "however, that the usual set over extensive areas was much greater at that time than diiring recent years. The existence of such a condition also is born out by statements of a number of old time oystermen who have worked the beds for the past half century^ The extensive water voli;imes moving over great areas of the open bay and Isjrger tributaries where most bottom areas are un- suitable for oyrjter growth undoubtedly have always caused a wide dis- persal of larvae in certain areas with the result that oyster setting there has never been heavy. Since hydrographic conditions today are little changed from those of a century ago it seems reasonable to conclude that the ratio of surviving set to brood stock in these areas of low setting probably has not changed^ Records again are unavailable but it can be assumed that the present oyster populations in these depleted areas ai'e not more than a tenth of those that once occupied the former virgin beds of accum'ulated oysters . It would follow then that the expected set in these areas also wo\ild not amount to more than a tenth of its one time proportions o T"nl5 condition, plus the fact that isolated single oysters do not spawn effectively, may well be the primar-y reason why setting now is almost a complete failtire over many once productive barso In addition to placlr^ more clean cultch at the right time in the most favorable setting ai-eas it would seem worthwhile to discover whether or not the rate of setting might be stimulated tlirough permitting larger brood reserves to accijmulate in designated ?eed ar'eas where dis=- persal of larvae to ot'ner water masses would be at a minimum » Should such increased accumtilation of brood stock show no effect upon intensity of setting or should the rate of setting become excessively high then the excess brood reserve could be utilized as seed. The success of such an attempt is of course entirely hypothetical but its practicability could be determined through setting up a well planned field trialo The ^36« use of small enclosed and artificially fertilized ponds for production of seed oysters might also be a possibility and would offer opportunity for experiments vith selected brood stock. Unfortunately facilities for this type of experiment are not now available in Maryland o While the careful selection of areas for shell planting, the avoidance of excessive fouling through favorable timing of the planting operation, and the assurance of sufficient or improved brood stock all are methods by which seed production in Maryland \mdoubtedly can be much improved^ it is felt that favorable combinations of hydrographic, meteorologic and biotic conditions often may embody the principal factors that determine the magnitude of the oyster set. Our present knowledge of such factors is very limited and there is need for much additional research that will help in designating and evaluating the effects of eacho Though many, such as wind movement, may be beyond man's control, it is possible that some yet to be isolated but im- portant factors may be susceptible to a practical manipulation that co'jld greatly increase the chances of successfiH oyster setting once the mechanism by which they operate is understood. It is felt that the greatest hope for markedly improved sets in Maryland depends largely upon the gaining axid application of such knowledge o .^7= SETTING OF OYSTERS IN VIRGINIA Jay" D o Andrews Virginia Fisheries Laboratory, Gloucester Point I. Introduction North of Chesapeake Bay, one of the foremost problems of oyster planters is to ottain a regular supply of seed oysters; to the south, the problem becomes one of how to handle an overly abundant set. Vir- ginia is the most northerly state with an adequate supply of seed oysters, and setting should not be a problem. The natural, set will suffice if proper steps are taken to catch and utilize it. We are most fortunate in Virginia in having a consistent set of moderate intensity resulting in high quality seed oysters. At present only the best seed oysters, those from the James River, are being used; a large portion of these are wasted, almost deliberately, by sacrific- ing them to predators o The public oyster grounds include most of the natural oyster beds. Being hard shelly bottoms with a natural set, many of these are being put to their best use as seed-oyster grounds. Private grounds, often lacking in natxiral set, or with the set destroyed by predation, are usually suitable for growth and fattening only. While the logical procedure is to move oysters from public seed grounds to private grow- ing grounds, in practice only the James River is used as a seed ar^a. Tributaries, such as the Corrotoman and Piankatank Rivers, which woiild make good seed areas, .despite poor growth are used as growing and fattening grounds. Other pijblic grounds, such as the RappaJiannoek River, have rather poor setting and oysters are sparse. The first studies of oyster setting in Virginia waters were made by Loosanoff in 1931* From 19^0 to 19^5 j Menzel, Hopkins, and Mackin collected some records. In the past eight years fairly intensive records of setting and survival have been collected from the three major tributaries in Virginia, the James, York, and Rappahannock Rivers. II. Setting a. Seasonal. Patterns of Setting In Virginia setting usually begins the f ix'st week of July and continues until about the beginning of October-- a period of 90 to 100 days (Andrews 1951) » Setting is continuous in the James, and nearly SO in the York, but in the Rappahannock' it may stop for several weeks dmjing the season. Two periods of heavier seti^ng can usually be dis- tinguished, the first in mid-Jiily and the peak of the second from the Contributions from the Virginia Fisheries Laboratory, No. 53- -38- middle of August to the middle of September „ In each of these periods, covering three or four weeks, settir^g graduaJLly tuilds to a peak and falls almost as slowly. In the James the early set is animportant==amo"jnting to less than 10 per cent of the total set. The late set up.ually reaches a pesJc about the first of September. In the York River, early and late sets may be of equal magnitude although often the late is more intensive. In the Rappahannock River, the early set, although small as compared with the other rivers, is the most consistent and important. Only rarely does a late set of any consequence occur. The first good set in the upper Rappahannock in ten years, in 195^, was late in the season. Fur'ther up the Bay in Maryland waters, the pattern for the Rappahaanock River seems to apply, with early sets of low magnitude predominating but occasional late sets of good intensity. An interesting feature of setting in the Virginia rivers is the uniformity in a particular season of the time pattern thx-oughout each river. As many as ten stations have been followed for setting pattern in the James River. Usually, the peaks and lows of setting occur in the same week for all stations in a river. While in a particular week the acttial amount of set varies greatly from one station to another, the relative intensity of the set from week to week is simiJ.ar for all stations. This pattern of timing and in,tensity of set suggests that the same broods of larvae are providing spat- fall for the whole river. b. Intensity of Setting The methods of estimating the amount of set or strike vary with the pur'poses for which the data are to be used. For the commercial oysterman, a count of spat on natural culch in late fall or early spring suffices. For the scientist seeking causes and explanations, it is desirable to know the initial set as well as the surviving set at later times. Too often no distinction is mad.e between initial set and sur- viving set. We have found that the number and size of spat on collectors at the end of two weeks exposure are often similar to that found at the end of one week. It is evident that in these samples most of the spat setting the first week had died by the end of the second. Three different records of the quantity of set have been taken in Virginia. First, weekly exposui'e of collectors is assumed to approximate initial set. For this count 10 to ko marked shells are mixed in a wire bag with about a quarter of a bushel of filler shells. Second, s'orvival or seasonal records are obtained by exposing shells of uniform size and quality in wire bags thi'oughout the setting -Eeason, All the spat on a quai-ter of a bushel of shells are counted. Third, the surviving set on natural culch is obtained each faJ.! from samples dr'edged from public grounds. All the spat on samples iTom one=quarter '39= to one iDushel in size are counted. Samples of each of these three kinds of records, from the best seed^^ound in the James River, are snown in Tatile "IT" Table I. Samples of Records of Setting On Wreck Shoal James River, Virginia (Number of spat per shell) Total of weekly Set in seasonal Set on natural Yesir sets for season shell bags c\ilch 1947 313 13 3-6 19^+8 308 9 3.5 19^9 215 15 7.'+ 1951 80 8 6A 1952 80 6 3-8 -1^0- In the James River, total weekly sets for a season may exceed 300 spat per shello For weeKly setting records, clean culch id exposed each week, ^o that this figure represents a setting rate or potential set -under nearly optimal conditions » Luring peak setting weeks, sets of 60 to 75 spat are obtained on individual shells . Seasonal, sets on individual shells in wire "bags seldom exceed 15 spat per shall <, The average seasonal catch for natural culch is usually less than five spat per shello The coramerciEil set is re- duced to a small percentage, usually less than five per cent, of the initial set. In the York and Rappahanrioek Elvers ^ initial set is con= sideratly lower ^ survival somewhat better except where drills are active, and the commercial set lower than, in the James- An average of one spat per shell is seldom exceeded on natural culch. Some of the smaller tributaries obtain a better set but as yet none studied . exceed the James in amoimt or consistency of setting. In the absence of dr'illSj, it appears that the survival rate increases as the strike decreases, although nowhere in Chesapeake Bay is setting so heavy that serious crowding is encountered. Svt- vival increases on up-river grounds where salinities ar-e low. At Deep Water 'Shoals in the James, the set is quite low, and dependent upon salinity conditions, but survival as high as 80 per cent has been recorded. It appears that late=setting spat survive better than early set, despite overwintering at a smaller size-^often 1 to 3 millimeters o Wherever oyster drills are present, the survival picture is violently upset. In the James River only Brown Shoals, the lowest of the seed beds, is infested. Scarcely any of the moderate set on Hampton Bar s'urvives. Drills are present in the lower parts of the York and Rappahannock Rivers, In the York, where the set is moderate, scarcely any survive beyond an age of three or four weeks. In the Rappahannock lower salinities hamper the activities of drills and losses are often minimal. c. Gradients of Setting While local variations from a variety of causes ai'e expected, it appears that in Virginia setting is heaviest near* the mouths of rivers and decreases progressively upriver (Table II), If coimts are not made soon after setting, a great many factors, such as predators .41= Table II. Vertical and Horizontal Setting Gradients, James River, 1952 Miles mouth above of river Total of sets for Num ber of spat per shell Ihore Bar weekly- season S\arviving set on seasonal shell bags Set on natural culch L Brown Shoal 90 5.6 2.92 R Dog Shoal 78 bags lost 1.24 White Shoal 3 k2 3-3 L Wreck Shoal 6 ko 5.8 3.00 R Days Point 6 11 3.8 0.51 L Deep Water Shoal 13 R Point of Shoal 10 h 3 2.6 0.26 0.67 ■k2- and silting^ tend to mask this gradient o There is also a heavier set on the left side of the channel (facing dovnriver) than on the right side J, probably related to the greater inflow of salt water on the left side. Most of the natiiral oyster beds are located on the left sides of the rivers o IIIo Brood Stock One of the factors often cited for failure of setting is lack of a sufficient stock of spawning oysters o In Virginia waters no one has seriously attempted to estimate the quantity of brood stock for a body of water o Wild popuJLations of adult oysters abound everywhere^ so that records of planted oysters do not include all the potential spawners. The importance of brood stock looms large in the minds of oystermen and the public. The methods suggested for utilizing brood oysters often include placing the biggest and oldest oysters obtainable in the most inaccessible places, such as the heads of creeks and rivers. This is probably ^oased on observations that setting is often good in the relatively enclosed waters of creeks o The source of the spawn for these sets remains unknown. In 1952 the Virginia assembly responded to this popular in- terest by providing a sanctuary for spawning oysters in the James River. The sanctuary^ not to exceed 1,000 acres, has not yet been established, but the question arises as to how such areas would be selected. The law provides that any area in the James River may be closed or opened to tonging according to the need. How would such areas be managed to insure thriving populations of spawning oysters? Would young or old oysters make the best brood stock? Woiold an area of this size be effective if thousands of acres of wild oysters were depleted? My own. opinion is that the importance of brood stock has been over'-rated, at least in southern waters. The process of oyster re- production is obviously a wasteful one. The amount of spawn may be far less important than physical conditions and the food supply for larvae, A comparison of the James and Rappahannock Rivers in Virginia illustrates this point. The James River always has a good set; a large population of wild oysters ;, mostly under two years of age, f-urnishes spawn. These oysters, in addition to being small, are always poor and produce very thin layers of gonadal material. Planted oysters are scarce in the James. In contrast, spawn in the Rappaha,nnock River comes from a large population of planted oysters up to five years of age. These oysters are typically fat and produce thick layers of spawn. The best oysters and a large part of the planted grounds are found in the upper Rappahannock River between Towles Point and Sharps, where setting is extremely poor. Wild oysters are also large and of good quality but not abundant. In 195^^ without any taiown change in the stock of oysters, a good set occ-orred in the upper Rappahannock River for the first time in ten years. A3. While the number of oysters is very large in the James, indivi- dual Rappahannock oysters greatly excell in the quantity of spawn produced. The "brood stock in the Rappahannock would seem optimal, tut setting regularly fails, whereas in the James River apparently inferior brood stock always produces a set. In attempting to provide large stocks of trood oysters, oyster- men may have failed to consider the spawning habits of their oysters. It is obvious that spawning patterns are quite different in the waters of Virginia and Long Island Sound. In northern waters spawning is concentrated in a few mass discharges. In Virginia some spawning must occur every few days for a period of three months. What pattern of spawning prevails in Virginia to provide setting larvae for twelve consecutive weeks of setting? The gradual build-up and decline in a period of heavy setting may consume as much as five weeks time. Un- less larvae live much longer than the 10 to ik days we assume at temperatures of 27 to 30° C., individual oysters must have many spawnings. Unlike oysters in northern climes, waiting patiently for water temperatures to reach a certain minimum level, oysters in warm waters may be able to conserve their spawn and release it gradually, thereby utilizing a long warm season. Is it not probable, that in their spawning habits oysters have become adapted to the climatological conditions of their native waters? Native oysters have usually ex- celled oysters from other waters in growth. The difficulty experienced by Loosanoff (personal communication) in getting Virginia oysters to spawn by artificial methods suggests that physiological differences exist. These differences may include distinct spawning patterns. rv. Distribution of Larvae The pattern of spatfall may be presumed to represent the final distribution of mature larvae during the last tidal cycle of their free-swimming life. The similarity of setting patterns implies that the same swarms are carried over each bar but that the oyster larvae are more abundant in the lower part of the swarTii. Since in our river estuaries new water is being added at both ends, the larvae must select a favorable stratum for transport upstream, or be continually lost from the system at the lower end and become progressively less abundant upriver (Pritchard 1951) • Pritchard noted that in the James larvae were more concentrated than would be expected from a considera- tion of the mixing processes. I believe that in studies of the distribution of oyster larvtie, too much credit has been given to the activities of the larvae and too little to the physical system of c\n-rents, tides, wind, and turbulence. Perhaps the studies of the Chesapeake Bay Institute are a step in the right direction. I am inclined to believe that larvae are distributed passively, with their own active motion essentially limited to vertical =UU- migrations o The roiled water on the l>ottom of the James River, some- times two feet deep^ would seem to be a. mopt inhospital'-ie place for larvae to rest when the tide is running. The gradient of setting which appears to exist in Virginia rivers is indirect evidence of passive distritutiono In addition to the local variations mentioned^, there are also "pockets" "-turnB in the river==which tend to trap lar-vaeo Each of the three rivers studied has one of these "pockets," which frequently have the highest sets in their respective rivers. There are such "pockets" in the James River at Jail Pointy, in the York at Gloucester Point, and in the Rappahann.ock at Towles Point. In 1950, in cooperation with the Chesapeake Bay Institute of The John Hopkins University, an intenf,-ive survey of oyster larvae in the James River was made. The time was chosen to coincide with the heavy set which occurred about the first of September. One- himdred liter samples were taken every two hours and sometimes every hour for a continuous period of three dayso At Wreck Shoal, where sets were averaging Uo spat per shellface per week (80 per shell), late umbo and eyed larvae were found infrequently; many samples both from tottom and surface waters had no larvae of any size. Samples of 500 liters did not improve the catch of larvae. It would have been quite possible to have taken daily plankton samples and found no larvae. Apparently larvae were not evenly distributed throughout the waters of the river, although a characteristic of setting in the James is the similarity of timing and relative intensity of setting for all tars. Some evidence was adduced that in successive tidal cycles the same larval swarms passed over beds several times (Pritchard 1953). Pritchard calculated that only one late stage larva per 100 liters of water is needed to produce the sets observed in the James. A compari= son with published accounts of larval studies leads to the conclusion that larvae are relatively scarce in the Jsmes River = Yet, setting is adequate and consistent from year to year. Probably the explanation lies in the long setting season, which allows numerous relatively small broods to be released, thus increasing the chances of circumvent= ing the vaxious factors of attrition. 45= Literature Cited Andrews, Jay D. 1951« Seasonal patterns of oyster setting in the James River and Chesapeake Bay. Ecology 32 (h): 752-758. Pritchard, Donald W. 1951« The physical hydrography of estuaries and some applications to "biological problems. Trans. North Amer, Wildlife Conf., 1951. pp. 368-376. Pritchard, D. W. 1953- Distrihution of oyster larvae in relation to hydrographic conditions. Proc. Gulf & Carib. Fish. Inst., 1952. -k6- THE GENERAL PAPTEPJ- OF OYSTER SETTING IN SOUTH CAROLINA Go Rotert Lunz Bears Bluff Laboratories j, Wadmalaw Island^ South Carolina The general pattern of oyster setting in South Carolina has been presented (McNiiIty, 1953 )» In this report McNolty summar'izes the spatfall per square inch of surface on shells which he exposed for two weeks at various depths throughout the year in regular wire "basket collectors » He ali^o included data on similar studies made by Green^ Grice, Cox^ and others at Bears Bluff in previous years. Generally speaking, the picture which McNulty gives holds true for the greater part of South Carolina waters o He states "The present study and data collected at this Laboratory over a period of many years indicate that spatfall in excess of one percent of the seasonal total ca.n be expected from early May through October o « « » " o The largest number of spat setting on a square inch of shell in a two week interval;, as given by McNulty (1953) Is 19<,4„ This is an average for ten shells at a minus one foot elevation during the last half of June 1951, Because of the great difference in size of shell used for ciiltch, setting figures at Bears Bluff Laboratories have always been given in numbers of spat per square inch, McNulty has explained "csSJe- fully the method used to determine the number of square inches of sur- face in test shells o He found that rough linear measurements of width times length was just about six percent less than actual surface area of the shells. Since this error is reasonably constant it has been disregarded. Shells used as experimental cultch range from 2,75 square inches to 13,75 square inches j the mean of several hundred shells was between U.5 and five square inches. Thus, for practical purposes, published and unpublished records at Bears BlxrFf pertaining to spatfall given in numbers per square inch can be multiplied by five to give the number of spat per shell. Even with this computation factor it is difficiilt to compare South Carolina records with other states, because it appears generaJ.ly from the idterature that experimental cultch in other states has a greater surface area than the shell used in South Carolina, From an admittedly preciirsory examination of some of the literature giving the spatfall in other states and converting the figures given by mathematical computation, plus some guess work as to the size of the experimental cultch used, the following table of spat per square inch for a two week interval has been derived; =1^7^ Table I. Spatfall "by States State in two weeks Reference Florida 35 Ingle (l95l) South Carolina 19 McNulty (1953) Spat per square in two weeks inch 35 19 2 to 69 5 to 9 3 to 5 3 to 5 North Carolina 2 to 69 Chestnut & Fahy (1952) Virginia 5 to 9 Andrews (l95l) Maryland 3 to 5 Beaven (1953) Connecticut 3 to 5 Loosanoff & Engle (19^0) Regardless of its position in relation to the other states along the Atlantic Seaboard^ one of the problems of oyster cultivation in South Carolina has to do with this spatfall. South Carolina spatfall may "be less intense than in Florida and North Carolina and greater than that of the other states to the North hut, due to the almost continuous spat- fall from May through Octoher coupled with an apparently high rate of survival of the young oysters above low water mark, it is extremely difficult to cultivate anything but cluster or "coon" oysters suitable primarily for canning. The vast majority of all oysters in South Carolina grow between the tides. There axe many explanations as to why this is so. Some of the contributing factors are definitely unknown. Transplanting mature oysters to below low water areas is impracticable. Planting of cultch shells below JLow water is likewise impracticable. Information at Bears Bluff Laboratories shows that there is a set of young oysters below loy water mark. However, at depths below the minus two feet elevation this set is not only less than that above low water mark but it is not as long continuing. Sixrvival of young oysters below minus two feet is extremely small. There is a great need for a complete study on this in South Carolina. Data from some experiments show a mortaJ-ity at plus one foot elevation from October to March of 5 per cent in young oysters set the previous July. Another study on oysters set in August showed a mortality from November through Jxme of 21 per cent at the jplus"" one foot elevation. -1+8. These same data show a mortality from October to March of 50 per cent at a minus 5 foot elevation and of 70 pe^ cent at a minus 8 foot elevationo For the November through June checks the mortality at minus 5 feet was 6k per cent and at the minus 7 feet elevation was 68 per cento Certainly some of the deaths are due to the usual run of pests o Oyster drills (Uro salpinx and an occasional Eupleur a) are present but they are not a";;undant and their distriBution is spotty. Menippe, Calli- necteS ;, and Panopeus are sericus pests both above and below low vater mark. Boring sponge \Cliona) is extremely abundant at and below the minus one foot elevation but apparently it does not attack young oysters » Dermo - cystidium has been recorded from South Carolina but it seems doubtful that this fung"'as is the cause of the high mortalities of spat below low water o Nothing is known of the newly described fungus reported by Davis et al. Starfish attacks on oysters are practically unknowrio Fouling by barnacles and mussels is limited. A bryozoan and a tubular ian are some- times quite heavy below low water mark. A small dark green sea anemone is^ in some areas, very abundant above low water. Mud and silt are a scoTorge which must be seen to be appreciated. Alan Stepherison of Wales described the effects of mud and silt in South Carolina by saying that South Carolina oysters stand up righteously, praying to keep out of the ever encroaching mud. Their children survive by standing on the shoulders of the parents. The general j)hysiographical features and meteorological conditions in South Carolina certainly play an important part in oyster cultivation. There are few rivers which bring down fresh water. Most of the oysters grow along the banks of small creeks and so-called rivers, which are really arms of the sea penetrating the half^submerged marsh lands. Rainfall and some nmoff from the adjacent high lands lower the salinity, but normally the salinity is high on most of the oyster producing grounds. It ranges from 20 to 3^ °/oOo Normal annual rainfall is ^7.25 inches but for the past few years this has been greatly reduced. This year to July 1, a deficiency of 9.h'J inches has been recorded. Water temperatures range from a low of 10° to a mean high of 33°C. Temperatures exceeding and remaining above 20°C are reached by March and last through October, The current velocity is fairly great, being in the neighborhood of 3 to k miles an hour. The tidal range is from k.S to slightly over eight feet (6.0 feet at Beai's Bluff) over the oyster grounds. Even in years of reduced rainfall, tur'Didity at Bears Bluff averages 95 parts per million of silicon dioxide with a minimum of 65 and a maximum of 125. This turbidity is caused to a large extent by detritus and silt in suspension plus, of cotirse, zooplankton and phytoplanicton. The combined influence of these physiogr-aphic factors in the environment together with the activities of oyster pests, pltis the in- fluence of some as yet tinknown enemy of the oyster, result in a greatly reduced set of spat in South Carolina below low water mark. This set =49= has a low survival. Set above low water mark is quite heavy and survival is high. This, coupled with a possibly inherent quality of South Carolina oysters, results in groups of clustered, thin billed, elongated oysters all growing from slightly below low water mark to two or two and one- half feet above low water mark. This situation makes it diffic\ilt to ^row anything except oysters useful as canning stock. The South Carolina oyster industry has learned to make use of this stock reasonably well and, yearly, between one-half and three-quarters of a million bushels of oysters are gathered, which yield to the fishermen somewhere in the vicinity of a half million dollars. -50- Llteratiire Cited Andrews^ J, Do 1951° Seasonal pattern of oyster setting in James River and Chesapeake Bay. Ecology 32(4); 75I10 Beaven, Go F. 1953» Oyster Bulletin No. 10, Chesapeake Bio, Lab. Chestnut, A. F. , W. E. Fahy. 1952o Studies on the vertical distri- bution of setting of oysters in Worth Carolina. Proc, Gulf & Carib. Fish. Inst., 5th, Ann. Sess., ppollO=lll. Davis, H. C, V. L. Loosanoff, W. H. Weston, and C. Martin. 195^. A fungus disease in clam and oyster larvae. Science 120 (3IO5) 36-38. Ingle, R. M. 1951« Spawning and setting of oysters in relation to seasonal and environmental changes. Bull. Mar-ine Sci. Gulf & Carli. 1(2): 128, Loosanoff, V. L., J. B. Engle. 19^0, Spawning and setting of oysters in Long Island Sound. Bull. U» S. B\ir. Fish. 49(33): 23U. McNulty, J. K. 1953" Seasonal and vertical patterns of oyster setting off Wadmalaw Island, S.C. Contr. No. 15, Bears Bluff Lab,, p. 10. -51= OySTER SETTING ON THE GULF COAST Sewell H= Hopkins A. & Mo College^ College Station, Texas I don't know whether he realized it or not^ out the section of the coast which Dr. Loosanoff has assigned to me covers quite a bit of territory^ Whenever we outlanders come to New England, we have a little difficulty getting the proper perspective established^ so I had better begin with a few comparisons of distances. The total distance along the outside coast line (without including any bays or islands) from Port Isabel, Texas to the southern tip of the Florida mainland is roughly the same as the distance along the Atlantic Coast from Maine to Miami (1660 miles). The 370 mile Texas coast extends through nearly four degrees of latitude; that is, there is about the same difference in latitude between Port Arthur and Brownsville as there is between Woods Hole;, Massachusetts, and the Eastern Shore of Virginia. Lest any- one discount that statement as a "Texas brag", I hasten to add that the Gulf Coast of Florida (the Giilf Coast alone, not the whole coast line) is twice as long as the Texas coast and extends through about 5'2 degrees of latitude; the difference in latitude between Pensacola and Oyster Keys on the south tip of the Florida mainland is about the same as the difference between Woods Hole and North Carolina, Any way you look at it, the territory I have to cover is equal to that represented by the six other members of the panel all put together. Because of the broad extent of the Gulf Coast and the great differences in climate along its length, there ajre not many specific statements I can make which would be true for the whole area<> There- fore I shall concentrate mainly on the southeastern comer of Louisiana, which is in the center of the Gulf Coast and is also the most important oyster growing region, with only a few remarks on other sections of the coast. The first point I want to make about setting on the Gulf Coast is that it is not an economic problem. In all of the oyster growing localities I have visited on the Gulf Coast, from Texas to Florida, spat set in great abundance every year and you could get more set than you could use by putting shells in the water almost anywhere any time. This being the case, the study of setting ceases to have any practical aspects and becomes piirely an academic subject. That does not make it any less interesting to me and I am glad that every new oyster biologist who comes to the Giilf spends a year or two investigating setting before he realizes that he is studying the wrong problem. We have acc\miulated a lot of interesting information that way. •52- The second point I want to mention is the fact that we have at least three species of oysters on the Gulf Coasto In addition to Crassostrea virginica which grows in the "brackish "hays and "bayous, we have two species of Ostrea., frons and equestris, which live in the Gulf, and sonietimes in the lower portions of the saltier tays of Florida and Texas, These two little Gul.f oysters are not considered to he of any value on our coast, where they have to compete with the much faster growing and more ali-undant Co virginica , 'but they actually grow faster and reach a larger size in the Gulf than the valuatle Olympia oyster does on the Pacific Coasto They do not grow as fast in the "bays, where they ar-e out of their no:rmal habitat, as they do on offshore structures in the Gulf, Ostrea equestris and 0.. frons have Deen studied recently Ly Gordon Gimter, Philip Butler j, and Winston Menzel, They are of interest to this group only "because their spat set in great numbers on ciiLch material in some "bays, and have probably been coionted along with the spat of the commercial oyster by some of the biologists who have studied setting in the past. This complication must be kept in mind when reading old, publications on setting in the Gulf and South Atlantic states « So far as I know^ Winston Menzel was the first to distinguish between our three species in the prodissoeonch and early spat stages » The prodissoconchs of Crassostrea virginica , Ostrea equestris , and Ostrea frons differ in color and in three dimen- sional form as well as in outline. A study of the vertical distribution of setting of the two species, C_„ virginica and 0. equestris, at Port Aransas, Texas ^ during a high salinity period, showed that Go virginica spat tended to set in greatest abundance near the surface, while 0. equestris setting increased toward the bottom. In another observation the vertical distribution of setting of £■> virg inica^ 0. equestris , and Oo frons was compared in one of Philip Butler's experiments at Pensacola<. The spat were identified and counted by Menzel » The salinity at Pensa- cola at the time of this experiment was not as high as it was at Port Aransas in the previoios experiment and we see that £o virginica spat were most abundant about 1^ to 2 meters above the bottom, rather than at the siorface, while the Ostrea spat showed an even stronger tendency toward concentration at the bottom than they did in the Port Aransas experiment. Neither Port Aransas nor the Pensacola station are in commercial oyster producing waters » In the high salinity waters near the Gulf £. virginica grows only in the intertidal zone, that is, above low tide level. Many spat do set below low tide level, but very few survive as long as a year. As we go inland from this high salinity zone, in Texas or in Louisiana bays, we pass into what I call the "transition zone" where C, virginica sets and survives both above arjd below low tide level, and where some populations maintain themselves from year to year on sub= tidal bottoms in spite of a high annual mortality caused by predators, parasites, or both. At many stations in this transition zone we get a fairly even distribution of setting from surface to bottom, but the =53"= survival of spat is so much "better just aTDOve and just "below mean low water level that crowded populations of oysters occur at that level and much thinner populations live at lower levels. This changes as we go siill farther- inlsiHdj, more oysters livir^g'STibtidally and fewer ahove low tide level, and we finally pass into the low salinity zone where there are no oysters visitle at low tide "but there are prosperous "beds on the deeper bcrttoms. I "believe;, although I have no experimental data to prove it, that in the upper part of the low salinity zone, near the extreme inland limit of oysters, the setting of £» virginica is con- centrated near the "bottom in the deeper water, just as that of 0. eques- tris and 0. frons is in the high salinity zone. Many of the published reports on setting do not distinguish clearly Tsetween "setting" and "setting and survival". From the stand- point of" oyster management or ciilture it is not necessary, "but as an academic type biologist I should like to have this distinction recognized. When you put out culch "before setting starts and do not go "back to look at it until the spat ai'e half an inch long, you are not studying setting, "but "setting and survival" o If you want to get data on actual setting you have to look at your culch at least once a week, and preferably every day. Even this will not entirely eliminate the survival factor, but it reduces it as much as is usually practical in field studies. Some data based on weekly or biweekly examination of cultch experiments in Louisiana shows the average number of spat setting per shall per day in Bay Sainte Elaine, a small body of water on the west side of Terrebonne Bay^ One count goes up to 90 spat per shell per flay. Higher numbers can be obtained by examining the culch more frequently. On one occasion Dr. Menzel tried leaving fresh shells in the water for only 2 to 2k hours before examining them, and got counts as high as 17 spat per shell per hour. Unfortunately he did not think of doing this until after the big peak of setting was past, or he might have gotten some really sensational figures. Several peaks of setting occur during the season, but the first one;, in late April or early May, is by far the biggest one and the last peak, in October, the smallest. There is a s"urprisingly close correspondence between the setting data and Djr. Hewatt's counts of larvae in plankton. I should like to emphasize again that these data are of strictly academic interest and have little if any application to oyster manage- ment or oyster culture problems. For instance, there is no pcjint in getting an oysterman to put out shells in time to catch the peaJc setting. Shells put out later will "wrap up" with more spat than anjo^ie can use, and most of the early set are soon killed by predators anyway. Young spat have a terrific mortality during the summer and most of them go to feed Stylochus , Thais , mud crabs, blue crabs, stone crabs, and fishes such as pinfish and sheepshead. In some areas a sampling program has given us average counts of two Thais per square foot on njitural and planted oyster beds. On the other hand, the spat of the scanty October -5^- set have a good siorvival and "by next spring they are practically as large as the May spate All spat which sxarvlye until fall have a good survival through the rest of their first year of life; it is not until their second year that they begin to suffer mortality caused "by para- sites . On the Gulf Coast Crassostrea virginica reaches sexual maturity when one month old. It spawns in April or eajrlier, and setting occurs from April or May to October or November -- at least half the year. Spat set in enormous numbers almost everywhere during this long season. All they need is cultch material, and since it malces little difference when you put shells in the water or where you put them — as long as they don't get buried in mud ■== setting is not a problem for the econo- mic biologis-t. The important economic problems for the Gulf Coast oyster biologist are survival and growth -- survival of the spat to seedsize, and growth of seed to market size as early in their second year of life as possible. Good management in the high salinity and transition zones requires that oysters be marketed before they are two years old. Only in the low salinity areas -- where salinity is usually below 15 and often below 10 °/oo -*~ can you keep oysters more than two years without excessive mortality. It is possible on the Gulf Coast to raise oysters from setting to market size in two years, or even in one year if you pick the right time and place. Oiir most important problem is to get growth like this every year, and thus get high yields; setting is not an economic problem with us. But it is fascinating to study, just the same. =55- DISTRIBUTION OF OYSTER LARViiE AH) SPAT IW PJIATION TO SOME EWVIRONMEMAL FACTORS IN A TIDAL ESTU/^RY * J. E» Mauming Marylaxid Department of Research and Education, Solomons H. H. Whaley Chesapeake Bay Institute of Johns Hopkins University, Baltimore, Maryland In 1951 "the Chesapeake Bay Institute and the Chesapeake Biologi- cal Laboratory collaborated in a survey of environmental factors asso- ciated with the distribution of oyster larvae and spat in the St. Mary's River of Maryland. The St. Mary's River (Fig« l) is a tidal estuary opening into the Potomac River six miles northwest of Point Lookout, which marks the confluence of the Potomac and Chesapeake Bay. Width at the entrance is approximately two miles? maximum depth, thirty feet. The channel shoaJLs to 2k feet at Priests' Point, 21 feet at Seminary Point, and eight feet just before Lynch Island. Above the island, which is 8.5 miles from th^ entrance, the greatest depth is five feet. The mean range of tides is 18 inches. For many years the St. Mary's River has been one of the most productive sources of seed oysters in the Chesapeake area, perhaps second in importance only to the James River. Total water area of the river, not including tributaries, is about 6,^+00 acres. There are 1,5^0 acres of charted oyster bars, chiefly in the lower river, an4 many uncharted clumps of small, slow growing oysters in shoal water, parti- cularly along the eastern shore, where all shell plantings for prpduetion of marketable seed have been made, from Chancellor's Point to Martin Point. Locations of hydrographic and plankton sampling stations are shown in Figure 1, the numbers indicating the distance in nautical miles from the station to the mouth of the river „ Physical and chemical determinations made during the survey and considered in this report Include current velocities, salinity, and tem- perature, together with observations on wind and weather. Methods are described in Report No. 11 of the Chesapeake Bay Institute, "Data Report, St. Mary's River Cruise, June 19-July I8, 1951"" Plankton sampling was concentrated in four periods: j'une 26-29, July 3»6, July 9-12, and July 16-20. All plankton samples were obtained by pumping 100 liters of water through a net of No. 20 silk bolting cloth. Samples were preserved in two per cent fonnalin, subsequently neutralized and reduced to ten milliliters in volume. A one milliliter aliquot was transferred from each sample to a Sedgwick-Rafter cell, and counts of oyster larvae were made at a magnification of 100 diameters. ^Contribution 102 Chesapeake Biological Laboratory, Md. Dept . of Research and Education, Solomons, Md. -56- NO OF SPAT PER 50 CM^ JUNE 27-AUO 3 17 39 (AREA MEAN) POTOMAC RIVER Fig. 1. Locations of hydrographic and test shell stations, St. Maxy's River, 1951, showing distribution of set on test shells. 57 Duplicate wire mesh bags containing scr-'abToed oyster shells were exposed from J-one 11 t& August • 37 at EtaiTicms designated SI through S^, Figure 1^ and to August 10 at stations S5 through S13.. Shells were changed at approximately weekly intervals <> Exposures were continued through October 15 at stations S5^ S6, 89 s, SIO, and S12o Counts were made of oyster spat attached to the inner faces of test shells. During the period of the survey the St« Mary's River was characterized by sluggish circulation. Current speeds seldom exceeded 0o25 knots; the maximum speed observed was O.U9 knots. Bottom salini- ties varied relatively little between the mouth of the river and Horse- shoe Point;, with a decrease of about one to two parts per thousand at Martin Points Extremes recorded were 80 55 and 15 ^ ^3 parts per thousand. Temperatiires ranged from 21.U°C» to 30.1°C., with a positive gradient , in the upstream direction. For the purpose of presenting data^ the river has been divided into three areas which show distinctive differences in circ-ulation, larval ab-ondance, and spatfall. Figure 1 defines these areas: Area I^ the lower river^ below Chancellor Point; Area II, from Chancellor Point to Horseshoe Point; and Area III, above Horseshoe Point. Figure 1 also shows the total niMber of spat setting on 50 square centimeters of shell surface at each station and the average for all stations in each area during the period June 15-August 3» Statistical analysis indicates that the differences in average set in the three areas are real differ- ences, with probabilities of more than one hundred to one in comparison of areas I and II and better than ten to one as between areas II and HI. In Figiore 2 the sampling period means of oyster larvae and the setting rate of spat on test shells are plotted for each of the three areas of the river. In Area II the pattern of setting followed very closely the orderly buildup of late stage lai'vae , In Areas I and III correspondence between abundance of larvae and setting rate was less clear, possibly because of lesa intensive larval sampling. In com- paring the three areas there are, however, differences which probably cannot be attributed solely to sampling erroro In Area I a continupus decline in numbers of straight hinge larvae occui-red, whereas in Areas II axid. Ill the trend was upward, with the peak of abundance occurring earlier in Area II than in Area IIIo In numbers of umbonate larvae Area II greatly exceeded both Area I and Area III, by ratios cf 30 °1 and 20:1 respectively, yet in setting rate Area II was intermediate. During the last larval sampling period, July l6-=20, late stage larvae reached peaks of abundance in Areas I and II and declined in Area III, but in the period July l8=27 intensity of setting was greatest in Area III. Average setting rates for the three areas, in terms of number of spat per 500 square centimeters of shell surface per day, were: Area I, J; Area II, 135; and Area III, 316, Of the charted oyster bai's in the St, Mary's River, 88 per cent lie in Area I, 9 per cent in Area II, and 3 per cent in Area IH. . As noted previously, there are many uncriarted clumps of ^58- • ""-IK O CO ^ o (Q 1 CQ +J CQ -P " (U >- to ^ tin S O •-3 1 Z , 3 •>. . < -I W KK t- »- « < ■ W _l o e <9 s I I I I I I — I r ' r r f T I — I — r- > P II I I I I I — I r- o • ^ //^ o 3 . . o. X_l wo. v> z O •- «> < UJ < OJ 59 oysters in the river; however, the total acreage of these is small compared with the area of natural barso It is noteworthy that the lightest' set occtirred in the area of densest spawning population, while the heaviest set occurrfed ' ih^an' area where tsrood stock is re- latively very scarce. Consideration of certain physical characteristics of the es- tuary offers an explanation of the apparently anomalo-us relationships of setting intensity^ larval abtuidance, and distribution of brood stock. Figure 3^ a schematic representation of the longitudinal circulation of the river d"aring the period of the survey, indicates the existence of a mechanism which would account for net upstream transport of plankton. In the lower river, low-banked and open to prevailing; southerly winds, a lake type circulation prevailed, with inflow near the surface and outflow in the lower layers. In the narrower, more winding middle stretch of the river, protected by relatively high and wooded banks, a very weak net upstream movement of the water mass occurred. Only in the upper river was there a two layer system with downstream flow in the upper strata and upstream flow in the lower strata, similar to the system shown by Pritchard (1952) to exist in the James River of Virginia. In such a circulation system as that indicated by Figure 3 the change in mean water level will be governed by the degree to which evaporation compensates for excess inflow. Obvioiisly this complex circulation system favored net upstream transport of larvae. There is indicated also the likelihood of loss of larvae from the lower river into the circulation of the Potomac, where the oyster population is relatively very sparse. Thus it appears that Area I, in which the greatest spawning population of oysters exists, suffered a net loss of larvae in both upstream and downstream directions, while in Area II the larval population spawned in that area, augmented by recruitment from Area I, was transported slowly upstream, eventually being lost in part to the circulation system of Area III, an effective "larval trap" offering little ch_ance of escape. A relatively small number of late stage larvae confined by physical forces to Area III produced a heavy set. A much greater but partially transient popiilation of late stage larvae produced approximately half as much set in Area II. It is reasonable to assume that a major part of the larval population of the river originated in Area I, but in the lower river factors of di- lution and displacement resulted in greatly diminished numbers of larvae and a very light set. If, as indicated by data to be presented later, maturing oyster larvae occjr in maximal numbers at progressively greater depths. Area I would lose early stage larvae to Area II and late stage larvae to the circ-ulation system of the Potomac River. Figure k- shows the distribution of larvae in two vertical series of 100 liter samples taken at slack water on July 10 and Jiily 17» The data are smoothed by a moving average of three =- that is, the count C of larvae shown for any depth D is equal to (C^ +- Cj^fl ft ^ C^-l ft)/3. =60- -p I ft P o to cd o H -H il t O 0) tQ '§ c •H -P ;D 0) -p ^ ^ §> H O a Ti ;3 -p t:) •1-1 S OJ ,c to o ai • a; CO >• •H • K M •H [fl P^ - . cd On S H 61 o n n N n n n ■ in 1 r • f^ 'I 1 1 _ r 1 - 1/ ' o / <0 / ^ ? / [ - o «0 ♦ ' ' ■ in 1 - ^ r I O — M M * « • O— Nn^nWKCDOt (4i) Hlcl3a . n r / in n « 1 n /»> 2 n / "^ : ^i „ r / o n /■ • (0 \ tl 1 / rjl r ^ 1 «> /' t- - r "* 1 — ■ " - - — — ■ r 5 / ■ 10 « ^ : ■ri O m 1 1 1 a: 8§ O « — kJ a. UJ < _i OUJ — o o z o o3 0> c O 2 O K ' u a. UJ < _j Ouj rOH H — (O >- O (J. o d z o o I < -I o ID Z z> ^ lU O a Z 3 < 5 a: < -I UJ o z I »- i < K O (U •H OJ CQ I fix CQ O — M 10 «' M 10 a> O— csito^in (OKOOI o 59» In summary, during the major period of oyster spawning and setting in the St. Mary's River in 1951 the pattern of longitudinal circulation was strongly influenced by prevailing southerly winds. This circulation system, providing means of slow upstream transport and .insuring retention of larvae in the upper river, apparently was the major factor in deter- mining horizontal distribution of oyster larvae and spatfall. Some data have been presented which suggest that density of the water may be a controlling factor in the vertical distribution of oyster larvae. This proposition is thought to merit serious consideration, since it in- volves a direct relationship of fundamental nature. ^63= 75 X OF TOTAL. 50 STRAIGHT- HINOE LARVAE XOF TOTAL. EARLY- UMBO LARVAE 1 r 25 75 50 25 5 jowed that young oyster larvae cannot utilize green algae, such as CHl,orella, while larger larvae of the same species, after reaching the size of about 125 u, are able to do so. We had already made many observations indicating that larvae of several species, such as Venus mercenaria , Mya arenaria , Mytilus edulis , and even the European and Olympia oysters, can be grown on a diet con- sisting chiefly of Chlorella (Loosanoff and Marak, 1951) • Davis' experi- ments, however, definitely proved that bivalve larvae are able to utilize certain green algae. This conclusion was supported by another series of experiments in which clam larvae were grown on a unialgal culture of Chlorella, reaching metamorphosis in about 12 days. Since this alga was isolated from the sea water of Milford Harbor, it probably constitutes part of the normal diet of the larvae of this region. Further experi- ments showed that clam larvae also grew well, reaching metamorphosis, on pure cultures of any one of the following three flagellates : Chla - mydomonas sp . , Chromulina pleiades , or Isochrysis galbana (Davis and Loosanoff, 19537^^ " These studies demonstrated two important points, namely, that clam larvae can live and grow on a very restricted diet, actually con- sisting of a single species of algae, such as Chlorella , or flagellate, and that unlike oyster larvae they can utilize green algae during all stages of development. Oiir conclusions, obviously, differ from those of some European workers (Cole, 193^) who maintain that bivalve larvae do not possess certain enzymes needed for the digestion of cellulose of which the cell walls of algae, such as Chlorella , are made and, therefore, cannot survive on such a diet. .67- The next problem was to determine the effect of different con= centrations of certain food organisias upon the rate of growth ajad sur = vival of larvae. Prom some of our early experiments we already knew that if fed approxljnately 200,000 to 300,000 cells of small Chlorella, measuring only a'r^out 3 u in diameter;, per cc<, of water, the larvae would live and me1:araorphos?e„ However, we did not loiow whether the optimum concentration of food cells would he above or "below this range. To answer this question a series of cultureB of larvae of Vc mercenaria j each containing approximately 6, 5 individuals pei- cc», were given different quantities of food» The principle foods tried were a mixed culttire of plankton consisting largely of small Chlore lla, measuring only about 3 u in size^ and a unialgal culture of Istrge CMorella, the cells of which averaged ahout 8 u in diameter » As was shown "by the increase in size and survival of the larvae, the optlmijm concentration of food depended upon the size of the food cells (Loosanoff, Davis, and Chanley, 1953) » When large Chlorella was used the optimum concentration was approximately 50,000 cells per cc, (Figo l). However, approximately J+00,000 cells per cco of smaller cells were needed to maintain the growth of the larvae at an equal rate. The difference "between the length=frequency distribution of the larvae in cu-ltures that were given the optim-om concentration of food and those that were somewhat overfed is illustrated in Figure 2, which shows that the larvae given approximately ^4-00,000 cells of small Chlorella per cc, were, at the end of the tenth day, considerably larger than those that were fed approximately 750,000 cells,. As can be concluded from the similarity of the two c-arves, the data also suggest that the food value of U00,000 small Chlorella closely approaches that of 50,000 cells of the larger form. Were we to assume that the cells of Chlorel la of both spe- cJes were perfect spheres, the largest measuring 8 u and the smaller about U u in diameter, we would find that regardless whether we fed 50,000 cells of the large form or 400^000 of the small, the total volume of cells in one cCo of water containing larvae would be approximately 13<.^0 X iC-^mm^o Carrying this comparison further we may calculate that 750,000 cells of the small fonn have a total volume of 25,13 x 10°3inm-^„, which closely approaches the volume of 26, 8l x 10°3inm3<, of 100,000 large cells. As can be seen from Figure 1, the larvae fed these quantities of the two foods grew at approximately the same rate, and both cultures showed signs of overfeeding. It would be interesting to determine whether the addition of a s im ilar volume of other food forms per ec, of water would enable larvae to grow at the same rate. The larvae were lisually killed when the concenti'ation of food cells became too heavy. This concentration depended again upon the size and kind of cells. For example, a concentration of about 300^000 cells of large Chlorella per cc. of water killed approximately 90 per cent of the larvae within a few days and those that survived grew very slowly or not at all, as did the larvae in the unfed control. The volume of 300,000 =68= LEGEND • - SMALL CHLORELLA 190 LARGE ' , 400,000 /f 50,000 / / 160 / / ,^ 500,000 / /..■•■' / / r 750,000 170 / / / .•■ •' // / :? ' / CO q: o i' -• 100,000 Z J^ /■/ Z 150 /^// z 5 140 _l ' //// / dv> /» 130 /jv i/^/ ,» 300,000 / / ^,___,r--'-* UNFtD CONTROL V^ / ^^'* — ^^'^ 120 M^^,^^^^"" /''/.y^*^'' no fi^' 4 ft f 1 1 1 1 1 1 6 8 DAYS Fig. 1. Mean length of larvae of hard clam, Venus mercenaria , of different ages in cultures kept at the same population density of 6.5 larvae per cc. "but given different nimbers of cells of small or large Chlorella per cc. of water. 69 O po a: LEGEND 50,000 LARGE CHLORELLA 100,000 SMALL — 780,000 120 130 140 ISO 160 170 LENGTH IN MICRONS Fig. 2. Length- frequency distribution (expressed in per cent) of ten day old larvae in cultures kept at the same population density of 6.5 larvae per cc. but given different numbers of cells of small and large Chlorella. 70 cells of large Chlorella is approximately 80o43 x l,D°-^inm-^ <, When the concentrations of large Chlorella were increased to approximately ^<- 500^,000 or 700^00^ cells per cco total mortality occijrred sometimes within 2k hoxirso PIowe"ver;, when fed the much smaller form of Chlorella the larvae survived and grew comparatively well in concentrations as high as 750,000 cells per cco (?ig. l). The larvae sui^viving in heavily fed c-'olt-ores visually displayed some anatomical abnormalities which often made the larvae unable to ingest the foodo Perhaps these abnormalities were to some extent re«*- sponsible for the sur\'"ival of such larvae under conditions which were lethal to normal oneso In discussing the effects of certain concentrations of food organisms upon the growth and survival of larvae it should be remem- bered that the n^amber of cells given constitutes only one approach for estimating the value of the food formo It has been pointed out by other workers (Burlew^ 1953) and it heis also been noticed by us on nimierous occasions, that the food value of such forms as Chlorella may show con- siderable variations according to the age of the cuJLtijre, its density of population, and, of co\jrse, the media in which it is grown. While trying to standardize as many factors as possible in our feeding ex- periments we still have not tried to feed the lax^'ae with Chlorella cultures of one age onljo Comparable to the effects noted in adult oysters by Loosanoff and Engle (19^7) "we found thist clam larvae may be killed either by the cells alone or by the filtrate only of the food cultijre or, of course, by a combination of the two (Loosanoff, Davis, and Chariley, 1953a). Dense concentrations of the food affect the larvae both mechanically, by the cells interfering with the swimming and feeding mechanism, and chemically, by the accumulated metabolic products of the cells which are toxic to the larvae,, For example, in an experiment in which the larvae were kept jji millipore filtered sea water, the larvae grew well in a culture receiving 100,000 large Chlorella cells per cc, plus the media in which the Chlorella was grown, even though this concentration was somewhat above the optim^jm (Fig. 3, A) » However;, both the larvae receivirxg cells alone, filtered off "oj use of a millipore filter and resuspended in sea water, at the rate of 1,000,000 cej_Ls per cCo (Figo 3, D) and the larvae receiving the filtrate only from the above cells (Fig» 3, E) soon diedo The resuJ-ts indicate that the filtrate containing metabolites of the cells may be more detrimental than the heavy concentration of the cells themselves » This toxicity of the so l called external metabolites and their ecological effect have long been recognized by aquatic biologists (Lucas, 19^7) « In this experiment the larval culture receiving filtrate from relatively small quantities of Ch3.orella grew somewhat better than the unfed control, especially dxiring the first few days of life of the -71- z o o: o 170 160 150 140 Z e> 120 LEGEND A - COMPLETE CULTURE- BASIS 100,000 CELLS PER C.C B - FILTRATE ONLY - " " .... C - UNFED CONTROL D - CELLS ONLY -BASIS 1,000,000 CELLS PER C.C E - FILTRATE ONLY- - " ... no 1 90XDEAD lOOX DEAD 8 10 12 DAYS Fig. 3. Effects of whole culture of Chlorella , of cells alone, and of the filtrate only at two concentrations upon growth of larvae of Venus mercenaria. 72 larval culture (Fig. 3> B, C). Additional experiments will be needed to determine whether this growth was due to the suspended matter present in the water or to the ability of the larvae to utilize some of the dissolved substances in the filtrate. In observing the behavior of clam larvae we noticed that they showed both mechanical, or quantitative, and chemical, or qualitative, selectivity in feeding. By regulating the amount of food ingested the larvae kept in heavier- than-optimum, but still nonkilling concentrations of ■ food cells, often contained less food in their stomaclis than the larvae in lighter food concentrations. This suggests that larvae are not merely mechanical feeders but possess a mechanism by means of which they can control the food in- take. Nevertheless, if kept in a heavy concentration of food cells for a long time, the larvae lose this regulating ability and soon become choked with food cells. However, if these larvae were removed to clear sea water, they would, if not too serio\isly injured, expel the excess ingested food ajad continue to develop and grow normally if properly fed. -73- The ability of larvae to select food was observed when they were given a mixtiore of several food organisms "but showed definite preference for one of them., As an example^ given a mijcture of Porphyridium and Chlamydomonas the larvae ingested the much larger cells of C hlamydomonas while rejecting the small cells of Porphyridiumo Another problem was to find the optimum concentrations of larvae that should "be maintained in the cultures o In the early stages of our work it appeared that if cultures are properly attended and fed, the majority of the larvae even in rather dense cultures will survive and, although displaying a slow rate of growth will, never^ theless, reach metamorphosis » We now know that to some extent optimum, as well as maximum, concentrations of larvae depend upon the species, but such hardy varieties as Vo mercenaria can be grown having as many as 50 larvae per cc« of water » Although this is a much heavier con- centration than those advocated' by other investigators, who usually emphasize the danger of overcrowding, we have frequently reared larvae to metamorphosis in such densities and, on many occasions we have successfully grown even denser cultinreso We believe that, as far as carrying the larvae of some species to metamorphosis is concerned, the danger of overcrowding may not be as acute as believed. This opinion is shared by our colleague, Melboiirne Eo Carriker, of the University of North. Carolina, who has also succeeded in growing c-ul= tiores of Vo mercenaria at the above mentioned concentrations (personal communication) „ To verify our impression, and at the same time learn more about the effect of crowding upon larvae a quantitative experiment was de= signed to determine the survival and rate of growth of larvae in different concentrations (Loosanoff, Davis, and Chanley, 1953'b) = Larvae of Vo mercenai'ia were grown in concentrations of about 6c^, 13, 26 and 52 early straight hinge larvae per cco, with each culture re= ceiving the same quantity of food, namely, 100,000 cells of large Chlorel la per cco The larvae in all cultures showed a low rate of mortality and grew to metamorphosiSo However, the mean rate of growth of the different cultur-es had an inverse relation zo the population density (Figo h) o For example, on the tenth day the mean length of the larvae in the series of cultures containing 6,6^5,13, 26, and 52 individuals per cco was 162, 15^, 151 and li4-if u respectivelyo On the 12th day the difference between the two lightest cult^jres was even more pronounced. It is assumed that the slower growth in the more crowded cul- tures was caused by more frequent collisions between the larvae, which interfered with the feeding, by the deleterious effects of the greater concentration of the excretory products of the larvae accumulating in the water and, at least during the later stages, by competition for food, The effects of crowding were further demonstrated by the experi= ments in which the cultures containing either 6,5 or 32o5 larvae per cCo ^7i^^ z o q: o 3E o z UJ LEGEND A - 6.5 LARVAE PER CC. B - 13.0 " " 180 C - 26.0 D - 52.0 . * .-■■ 170 ^ 160 y-'c....- •■■' #•■■■"' ,. ^0 • 150 // ..■■■■ ".••■• 140 ■ // / / 130 A ..'■ .■•■■' 120 ■ y& / 110 1 10 DAYS 12 Fig. k. Mean length of larvae of Venus mercenaria of different ages in cultures kept at different popu- lation densities but receiving the same quantity of food per cc. of water (100,000 cells of large Chlorella) , 75 J were given what are considered optimum quantities of two kinds of food cells. Some ciiltiires received 50,000 cells of the large ChlorellSj, while the others received i^OO^OOO cells of the smaller fortn 'Jig. 5)„ The cul.tures containing 6„5 larvae per cCo grew quite rapidly on "both kinds of foodo The more crowded cultures, containing 32 „ 5 larvae per cc, grew well "between the second and fourth daysf suggesting that there was sufficient food for this number of larvae at this size, "but gr-ew much more slowly during later stages » At the end of 12 days they averaged only about 1^7 u, as compaxed with I89 and l8^' u for the two lightly populated cultures <> The discrepancy in the sizes of the larvae of the cultures widely differing In population density is fur-ther emphasized by com- paring the length" frequency distribution of ^he lar-vae. We may take as an example the ciatures shown, in Figure 5 that received 50,000 cells of large Chlcrella but differed in population densities o 3y plotting the length-frequency distribution of the larvae of these c-ultures at the end of the tenth day one can easily see that while the modal class of the lightly populated culture was approximately 170 u, that of the denser culture was only about 1U5 u (Fig. 6)0 Furthermore, while the maximum size of the larvae in the first cultur'e was at that time al= ready 200 u, the largei?t laxvae in the more crowded culture measured only 175 u,o It was also noticed that the range of lengths of the larvae was much greater in the lightly populated than in _the denser cultures o Earlier Davis (1953) came to the same conclusion in his studies of oyster lainrae^ £„ virginicao These e:jcperiments showed that as we thought previously, clam larvae yill grow and reach metamorpho sis even if heavily overcrowded (Loosanoff j, Miller aixd Smith, I951). However, present observations indicate that, contrary to our earlier opinion, the larvae in such overcrowded cultures will reach the setting stage later than those in less populated cultures » As a result of our experiments on crowding of larvae, the ques= tion arose whether the growth of larvae in overpop-olated cultures could be maintained at the same rate as in lightly popuiated ones by increas= ing the quantity of food proportionally to the increase in populationo Accordingly, experiments were conducted in which the increase in the larval population was accompanied by a proportional increase in the number of food cells » The cult-'Jires containing approximately 6=5 clam lajrvae per cco were given 100,000 large Chlorella cells per cCo per day; the cultures containing 13 larvae received 200,000 cells; 26 larvae re= ceived 400,000 cells and, finally, the cultures with 52 lai-vae were given 800,000 cells per cco per day (Fig. 7), At the end of the li4-th day the larvae in the least crowded culture averaged almost 190 u in length and. many of them were already metamorphosingo In the next least crowded culture, containing 13 larvae per cc. of water and receiving 200,000 cells of large Chlorella per cc, the larvae averaged only ? lightly over I50 u, even though the same num= ber of food cells per larva was available as in. the first culture. A majority of the larvae given ^00,000 cells of Chlorella per cc died within four days. Those fed 800,000 cells per ec. died within 48 hours, =76^ leo On some occasionir'5, r'ecently developed early straight hinge clam larvae vere kept ia cotton filtered sea water without receiving additional food for ab long as 1^ dayso The gr-owth of the&e lar-vae was, as a rule, considerably slowed down or entii'ely arrested, "but the larTTae themi5ej.vec remained noimai. in appeai-ance and continued to swim. If after such a long period of virtual star-vation the larvae were given food, they 'began to gr-ow and eventually reached metamorphosiSc Obviously, clam larvae can endure a near' starvation diet "better than overfeeding, M. may te concluded from this bhort report, the studies of clam larvae have already coa« iderafcly added to our understanding of the behavior of thei^e organisms, placing us in a position where we can now decide what, from a practical point of view, should 'be the most advantageous ratios in our cultures between the numbers of lar= vae and numbers of food cells of certain kinds. Future experiments should be directed towards making such ratios even more accurate by introducing a progressing correlation factor that would compensate for the increase in tne size of the lar'vae during the life of a cul= ture. We hope the information on the effects of temperature on the rate of gr-owth of lax'vae (Loosanoff, Miller and Smith, 1951), together with the present data concerning the optimum ratio of food to larvae, will soon give us definite formiilae indicating the most advantageous combinations of these factors for growing the largest number of clam set in the shortest time in small volumes of water. Even now, utiliz= ing our- present limited experience, we ar'e able to grew to metamorphosis approximately 1,000,000 small clams per month per five -gallon jar the bottom area of which is only about one sqiisre foot (Fig. 8) , Our present methods allow 'U£. to grow clamb during the entire year. There =■ fore, we can roughl,y estimate that a tingle jar can "!:;e used to grow approximately 12,000,000 clams per year provided we can keep mortality at a low level. Although we still do not kno^^/ of any efficient method for con= trolling fxmgi, such as S irolpi d ium, which at times causes heavy mor= tality among cur larvae, we are optimibtic enough to think that we may easily prevent and control man^ bacterial arjd,, perhaps, virus diseases which we suspect to be prevalent among the larvae. Our optimism is founded on the resui.tb of some of our' preliminary experiment? in which larvae were kept in water to which certain quantities of feulpha drugs or such antibiotics as procaine penicillin G or Chloromycetin were =80= Fig. 8. Battery of jars for rearing bivalve larvae. 81 added. Mortality of the larvae in cultures so treated vas usually lower than in the controls. Fijrther studies in this field will "be conducted at our lahoratoryo Clam sets obtained by the use of our methods should be free of the admixture of juveniles of other bivalves^ which in the early stages look almost the same as small V« mercenaria y and which later on will have to be removed, a slow and expensive process. The clams will also be free of external enemies, such as crabs, or borers, the larvae of which may set in natiire simultaneously with clams. Finally, the set will originate from known stock or, if necessary, even from known pairs of parents, as has often been done at our laboratory. From then on, if we learn how to control diseases of larvae and juvenile clams, the breeding of clams of desired qualities, such as rapid growth, high glycogen content, and resistance to certain diseases, will become commercially feasible. We wish to express our appreciation to our colleague, Charles A. Nomejko, for participating in some aspects of these experiments and for making the illustrations for this article, azLd to Miss Rita Riccio for her generous help in editing and preparing the manuscript. =82= LITERATTJKE CITED Blegvadj, Ho 1915 » Food and conditions of nourishment among the com- munities of InverteTorate animals found on or in the sea "bottom in Danish waters. Repto Danish Biolo Sta. to Board Agric. 22; Ul=78<. Binrlew^ Jo So (Editor) » 1953° Algal cultiore from laljoratory to pilot planto Carnegie Inst. Washo 1=357« Cole, Ho Ao 19360 Experiments in the breeding of oysters ( Ostrea edulis ) in tanks j with special reference to the food of the larva and spat. Fish, Invest. Series II, 15: 1-28, Davis, H, Co 1953* On food and feeding of larvae of the American oyster, C, virginica o Biol. BuJ-l, lOU: 334-350o Davis, H. Co, ajid V. L, Loosanoff, 1953» Utilization of different food organisms by clam larvae „ Anat. Rec. 117: 6^160 Loosanoff, V, Lo 1950. Variations in intensity of setting of oysters in Long Island Sound, Atlantic Fisherman 3O: 15-I6, h"]. Loosanoff, V. L., and J. B. Engle. 19^7. Effect of different con- centrations of micro-organisms on the feeding of oysters (O. virginica ) . Fishery Bull, h2, Fish and Wildlife Service 51: 31=57. Loosanoff, V. L., and H. C. Davis. 1950. Conditioning V, mercenaria for spawning in winter and breeding its larvae in the labor- atory. Biolo BuJ.lo 98: 60-650 Loosanoff, V, Lo, and R. R, Marak. 1951» Cultixring lamellibranch larvae. Anato Rec. Ill: 129-130. Loosanoff, V, L,, W, S. Miller, and P. B, Smith. 1951, Growth and setting of larvae of Venus mercenaria in relation to temperatiore < Jr. Mar. Res. 10: 59-=8l. Loosanoff, V. L., H. C. Davis, and P. E. Chanley. 1953a« Behavior of clam larvae in different concentrations of food organisms, Anat, Rec. 117: 586-587. Loosanoff, V. L., H. C. Davis, and P. E, Chanley, 1953b. Effect of overcrowding on rate of growth of clam larvae. Anat. Rec, II7: 6I15-6J+6, Lucas, C, E. 19^7» Ttis ecological effects of external metabolites, Biol. ReVo 22: 270-295. =83= POSSIBLE CAjBES OF GROWTH 7ARIATI0WS IM CLAM LARVAE P, Eo Chanley U. So Fish and Wildlife Service_, Milford^ Connecticut In recent years advances in larval research have greatly in^ creased the possioility of raising the hard clam^ Yen'os mercenaria , under hatchery conditions <> As the commercial cultivation of clams becomes increasingly feasiTjle^ numerous questions are raised aljout all its phases » Perhaps the most frequent questions concern the causes for differences in the rate of growth of lar^'aeo These causes may be those brought about by environmental differences and those that are inherited „ The effect of variation of environmental factors on the rate of growth of lajTvae has been studied to some extent. Thus, the effects of variations in temperature^ density of population^ and the type and quantity of food have been reported (Loosanoff, Miller and Smith, 1951; Carriker, 1952 j Loosanoff, Davis and Chanley, 1953a; Loosanoff, Davis and Chanley, 1953b; Loosanoff and Davis, 1953) » However, very little is known about inherited variations. Loosanoff, Davis and Chanley (l953c) reported that;, in general, there was no relationship between the age or size of the parent and either the size of the larvae or the viability of the spawn. They also reported that variations in both the viability of the spawn and the size of the larvae were common. Individual differences in larval size, within the same cultiure, have also been observed on many occasions (Loosanoff and Davis, 1950; Marak:, I95I1 Davis, 1953)" Since environmental conditions for all larvae, within the same culture, should be virtually identical, some of these variations must be caused by iiiherited differences- This study was designed to evaluate some of the effects of in= herited factors on the growth and survival of clam larvae. It should be emphasized, however, that this report presents the results of pre- liminary studies and, therefore, the conclusions are tentative and may need to be revised in the future. In the first experiment we compared the larvae from several combinations of parents to determine the influence of each pai'ent on the rate of growth of the larvae. Three female and three male Venus mercenaria were induced to spawn in the laboratory by Increasing the water temperature and adding millipore filtered sperm water. The eggs of one female (3) were then divided into three groups and each group was fertilized by the sperm of a different male. This resulted in the crosses = 3 x 1, 3 x 2, and 3 x 3. Sperm from 1 was also used to fertilize the eggs of the other two females ( 1 and 2), giving the crosses 1x1 and 2x1. Triplicate cultijires from each cross were then started, using approximately equal numbers of eggs, in 18 liter earthenware c\ilture jar's. These jai's were kept in a common water bath to minimize the temperature differences between the cultures. During =8U= the coiirse of the experime.it the temperattire ranged from 19 oO to 22ol C. ■but at no time did the mai^im.-om temperature difference between the jars exceed = 7°Co All cultures were fed equal quantities of Ch-lorella daily., Water in the jars was changed and lar^/aJ- samples taken at two day in- tervals » On the second, day;, after fertilization^ a count was ma,de to determine the percentage of eggs that had developed to nonnal straight hinge larvae and the population in each cultur-e was then adjusted to approximately 18G,000 to 200^000 larvae » The percentage of survival and the number of cultures continued for each cross are shown in Table I, Several factors were prooably responsible for the differences in the percentages of eggs that developed normally into straight hinge larvae o The length of time between the discharge of spawn and fertili- zation may be cited as an. example » We have found that the percentage of developing eggs decreased rapidly as the time interval, between spawn- ing and fertilization increased. This was apparently caused by the loss of viability of the sperm since smother sample of the same eggs showed a high percentage of development if fresh sperm were used. Since the first male spaT»med m-ore than two hours earlier than the last female, it is possible tlriat the differences in s'orvival in some of these crosses were partially due to the differences in the age of the sperm at ferti- lization,. It is also possible thiat mechanical damage may result from screening or transferriiag the eggs after cleavage has begun- This may be responsible for some of the abnormalities and lower rates of EurvivaJ. in this experlmentj, since some of the eggs had undergone cell division before all the cultiires co^uld be started. These factors cannot account for all the observed differences, however, for in the 1 x 1 cross the sperm was fresh and the same sperm^ used later in the day, initiated good development in the eggs of 2 and 3' Moreover, the eggs in the 1x1 cross were handled soon after fertilization and the cultures were started before cleavage had begiuio Nevertheless, such a small percentage of the eggs developed to normal straight hinge larvae that the e-ultures of this cress were discaj."dedc Since this female spawned A^ery lightly while the other clams spawned more heavily, it seems reasonable to suspect that the condition of the egjs was resporisible for their poor development. Possibly the eggs were immature. Davis (19^9) reported the release of imfflat-a.re eggs by oysters and loosanoff and Davis (l950) stated that, "Probably some clams were compelled by the stron.g temperature stimula- tion to abort the eggs even if the eggs were not fully ripe." on the other hand, clams can retain mature gametes for extended periods of time without the loss of viability^ Loosanoff and Davis (1951 ) found that normal larvae could be raised even when the gametes were not released until several months after the end of the normal spawning period. =85= Table I. Number of fertilized eggs used in each, cross, percentage developing to normal straight hinge larvae, and nuBiber of cultures continued for growth studies. TUTSC Egp- TOTAL PERCENTAGE NUMBER CROSS Cultured Normal Larvae Of Of Ciiltures At 2 Days Normal Larvae Continued 1 X 1 753,000 --- less than 10 2 X 1 1,638,000 672,000 h5 3 3 X 1 1,500,000 9^2,000 63 3 3 X 2 1,500,000 360,760 2k 2 3 X 3 1,500,000 180,000 12 1 -86- When two females vere crossed with the same male^ 2x1 and 3x1^ there was a significaiit difference in the size of the larvae at two days (Fig» l). Significance was determined by the lase of the "t" testo The "t" value was 13.0lif-, consequently the prohaDility was much less than oOOlo However, from the second day to the con= elusion of the experinEsntj, this "difference in larval size remained constant and consequently the growth rates were nearly identical. Since no similar difference in larval size at two days was recorded when one female was crossed with three males a;'jd since the rate of growth, after the second day^ was nearly equal in all crosses of this experiment J, it seems uiilikely that any inherited difference in rate of growth was responsiljle for the difference in size of the 2x1 and 3x1 larvae at two ciayso ¥e may conclude, therefore, that significant differences in the size of the lar-vae at two days are caused primarily "by some factor, such as the size of the egg. Such a concludion is, however, tentative since at present we have only limited data on the correlation of egg size with the larval size at two days a There was a consideralsle range in size within each culture although all the lajr/ae within a single culture were from the same parents » This size range increased with the age of the culture, as can he seen hy comparing the ler^th- frequency distri'Dution of larvae at two days with that of the same larvae at ten days (Fig.. 2) » Apparent- ly, then, certain individuals grew consistently faster or slower than average, although the environment must have "been virtually identical for all larvae within a cultare. Although the effect of possihle en= vironmental differences, within a culture, cannot he entirely eliminated, the range in length, observed in these crosses, must have been at least in part due to inherited differences. It would seem, then, that even among sibling larvae, there is a wide range of inherited differences that affects the rate of growth. In a repeat e:xperiment stripped sperm were used so that all sperm would be approximately the same age at fertilization. All eggs were placed in Jars before cleavage had begun, to avoid damaging the early embryos by screening. Temperatures ranged from 22,8° to 2^,3*^0. with a msjcimimi difference of 0,^ C. between jars at any given time. On the second day, popiilations were reduced to about 1^0,000 larvae per jar. Otherwise, the procediire employed was the same as in the first experiment o In the stripping process, the body fluids of the male are un- avoidably mixed with the sperm. It is not knowri haw these fluids affect the gametes or the developing zygotes. Some workers (j-ost, 1939) have demonstrated that, in other species, the body fluids interfere with the normal developmexit of the eggs. This danger was probably slight in our experiment, since the water containing the eggs and sperm was greatly diluted when the eggs were put in cultui-e jars. These fluids »87= 170 150 (A Z 2 "30 O 110 90 4 LEGEND • • $2 BY o'l • • $3 BY 0^1 6 DAYS 10 Fig. 1. Growth rates of larvae from two different femsiles crossed with the same male. Each point repre- sents the mean length of 100 larvae from each of tripli- cate ciiltures. 88 LEGEND • • S 2 BY 0" I • • S3 BY o" I 110 ijo 140 leo leo MICRONS 170 leo i«o eoo Fig. 2. Length- frequency distribution of the same two crosses at two and ten days showing the increase in range with the age of the larvae. 89 should not, in any event, have had any effect on the larvae after the water was changed on the second day^ The numbers of larvae were not equal in all cultures for the first two dayso There is no reason to believe that this affected the percentage of eggs developing to the normal straight hinge stage since the heaviest concentration was no higher than in many other experiments in which the development was normal o Nor is there any reason to be- lieve that this affected their growth during the first two days since there was no appreciable difference in the size of the straight hinge larvae with the possible exception of the larvae from the B x A cross o The larvae of this cross were somewhat smaller but so few developed that they were discarded , Triplicate cultures of the A x A and A x C crosses, duplicate cultures of the A x B cross, and a single culture of the C x A cross were continued for growth rate studies. The differences in the percentage of eggs that developed nor-mally must be primarily due to the condition of the eggs in this experiment o The larvae from the C x A cross grew more slowly than those from the Ax A cross (Fig. 3)^ and by the sixth day the difference was statistically significant, that is, the 95^ confidence limits did not overlap. Since the growth rates of these crosses were different throughout the experiment, the difference appears to have been caused by factors inherited from the female parent o The differences in rates of growth, when one female was crossed with three males, were not nearly as pronouncedo However, the difference between the mean lengths of the larvae from the A x A and the A x B crosses gradually increased and by the tenth day the 95^ confidence limits determined statistical signi= ficanceo (Figo k) o This difference must have been the result of in= herited influences of the male parent. The mean lengths of the larvae from the A x C cross are not significantly different from either the mean lengths of the Ax A or the A x B larvae, I would like to express my appreciation to Dro v"» Lo Loosanoff and Mro Ho Co Davis for their invaluable assistance in all phases of the worko I am also indebted to Miss Ro So Riccio and Mr, Co A, Womejko for their assistance in the preparation of the manuscript. SiJMMARY lo Significantly different rates of growth were found between larvae from the same female crossed with two different males and also between larvae from two separate females crossed with the same male. It is tentatively concluded that inherited differences from either of the parents may be responsible for these differences in the rate of growth. =90= 190 170 cn z o cr 150 o 130 no LEGEND $ A BY c/ A • • ? C BY d* A 1 6 DAYS 10 Fig. 3. Growth rates of larvae from two different females crossed with the same male. Points on the ^A x ^A line are mean lengths of 100 larvae from each of triplicate cultures. Points on the ^C x «J*A line are mean lengths of 100 larvae from a single culture. Shaded areas are the 95 per cent confidence limits. 91 210 190- LEGEND • • ? A BY ci* A . ^ ^/^ BY (3*8 • " ?A BY 0*0 y 170 Z o a: o 2 150 130 6 8 DAYS 10 12 Fig. k. Growth rates of larvae from a single female crossed with three males. Each point on the^A x ^A and ^ A X /C lines represents the mean length of 100 larvae from each of triplicate cultures. Each point on the ^ A x^B line represents the mean length of 100 larvae from each of duplicate cialtures. 92 2o Significant differences in the meaxi lengths of laj:"vae at two days were not correlated with subsequent differences in growth rate. It is tentatively concluded that these early differences are caused by physiological differences in the eggs. 3. The range of length of larvae, from a single pair of parents, increased as the larvae grew larger and older » Apparently, then, sitling larvae have widely different rates of growtho At least part of this difference is celieved to "be a result of inherited dif= ferenceso k<. The a"bility of sperm to fertilize eggs decreases as the time "between the dischar-ge of sperm and fertilization increases. Eggs remain fertilizable for a longer period of time. ■93" LITERATURE CITED Carriker, M. Ro 1952. Preliminary studies on the flpld culture, 'behavior, and trapping of the larvae of the hard clam, Venus ( Mercenaria ) mercenarda L. Nat. Shellfisheries Assoc. Conv. Add. 1952; 70-73. Davis, H. Co 19^9. On the culture of oyster larvae in the labor= atory, Wat. Shellfisheries Assoc, Add. 19^9; 33=38. Davis, H, C. 1953° On food and feeding of larvae of the American oysster, C. virglnica. Biol, Bull. lOht 33^=350. Just, E. E. 1939° Basic methods for experiments on eggs of marine animal s. 89 pp° Philadelphia; P. Blakiston's Sons & Co., Inc. Loosanoffj V. L,, and H, C, Davis. 1950. Conditioning V, mercenaria for spawning in winter and. breeding its larvae In Xlae laboratory. Biol. Bull. 98; 60-65, Loosanoff, V. L., and H, C. Davis. 1951° Delaying spawning of lamellihranchs ty low temperature, Jr. Mar. Res. 10; 197-202, Loosanoff, V, L., and H, C, Davis, 1953° Utilization of different food organisms by clam lar-vae, Anat. Rec. 117: 6h6. Loosanoff, V. L,, H, C. Davis, and P, E, Chanley, 1953a. Behavior of clam larvae in different concentrations of food organisms, Anat, Rec, 117: 586=.587. Loosanoff, V, L,, H, C. Davis, and P. E. Chanley. 195313. Effect of overcrowding on rate of growth of clam larvae, Anat, Rec, II7; 6i^5=.646, Loosanoff, V. L., H, C. Davis, and P, E, Chanley, 1953c, Wo re= lationship found "between age of oyster and quality of spawn, Atlantic Fisherman 3kt 22=23° Loosanoff, V. L., W. S. Miller, sind P. B, Smith. 1951. Growth and setting of lar-vae of Venus mercenaria in relation to temper= ature, Jr, Mar, Res. 10; 59~8l. Marak, R. R. 1951° Var-iations in sizes and rates of growth of lamellibranch lar-vae of the same par'ents. Nat. Shellfisheries Assoc, Conv, Add, 195I: U5, ^94= SELECTIYS SETTING OF O'ffiTER I.ftlRVAJ, OK ARTITICIAL GULTCH Philip Ao Butler U. S. Fish and Wildlife Service, Pensacolaj, Florida The consistently'- high oyster spatfall in the Guilf area sets this region apart from msziy other areas where oysters are cultured <> Since knowledge of the causes of success or failure of a set is of great importance to the industry, we initiated studies on this pro^ blem at the Pensacola Laboratory in 19^9° We made systematic counts of the time and frequency of spatfall in conjunction with continuous records of hydrographic conditions » This paper presents some of the general conclusions derived from a study of five years of data, es- pecially those relating to larval loehavior at the setting stage « It was necessary to select materials and methods for this study which would permit comparable resvilts over a period of years and not he cumbersome o The collection of spat on oyster shells while having many desii'able features has also some obvious objections, especially the difficulty of computing the exposure area. For this reason, several flat artificial materials were tested with the re-= suits shown in Figure lo We sanded the surface of the Plexiglas so its texture was compsxable to the other materials used, Thje fact that spat avoided the white Plexiglas is obviously not due to a color reaction, since th^e rates on black are nearly as low whereas the rate on white oyster shell is very higho We examined only the white surfaces of the oyster shells and carefijlly computed the area of the exposed surfaces, so that these data could be expressed as rates per square centimeter » The cement board, which received the highest set, is that commonly used for building purposes » It is easily handled and costs approximately one cent per 4 inch square plate o Such a plate provides one hundred square centimeters of ex= posed surface o We also tested smooth and rough s^Jirfaces and found over a long period th-£t each receives the same amo'-urit of seto Since the smooth surface of the cement board is so much easier to examine^ it is the only one we -used routinely,, In the five years of observations, we have never had a routine plate, that is one exposed for 7 days, without at least one sedentary animal form. We have hjad concentrations of oysters as high as 30 per square centimeter | that is rouglily comparable to a set of "00,000 per bushel of shell o Barnacle rates have at times been over 100 per square centimeter. In general, when the concentration of a species reaches Oo5 per cm or more, counting 10^ of the surface provides an accurate index of the total set. When oyster concentrations were below this figure, we examined from one to four full plates each week,. We wash the plates under a strong jet of water before examination so that any debris or animals not firmly attached will be removed » -95= OYSTER SPATFALL SELECTION OF SUBSTRATE PLEXIGLAS - WHITE PLEXIGLAS - BLACK H FROSTED GLASS OYSTER SHELL CEMENT BOARD 15 28 46 X Fig. 1. Percentage occurrence of spat on plates of different materials exposed for 7 day's. Plates were exposed simultaneously and adjacent to each other. Data include approximately 3jOOO oysters. 96 Figirt'e 2 shai.rs the rack containing cement "board plates which is exposed each week throughout the yearo In special studies, other racks of similar natrore carried plates at different angles. The racks hang halfway between siii-faca and bottom in three meters of water on one of our docks. Figure 3 shows a horizontal rack csxr'ylT^ different colored plates about 1^ meters below the water surface. This photograph indi- cates the usual clarity of the water during the oyster spawning season. One of the first things noted in our examinations was the pre- ponderance of spat en the upper s^jrface of exposed plates. Figure k shows the relative numbers of spat setting on upper and lower surfaces of plates exposed throughout the setting season for four years. I have included here similar data on barnacles becaiise of their probable cor- relation with the data on oysters. This figi.ire also shows the daily incidence of oyster spat on upper and lower surfaces of plates exposed for limited periods. Dark plates were exposed from 7°30 P.M. until 3°30 A.M. on consecutive moon- less nights, while light plates were in full sun from 7° 30 A.M. until 3:30 P.M. on the intervening days. These data are somewhat limited and the experiment will be repeated next siamHier, but it appears that the majority of setting in this area occurs in daylight hours and on upper surfaces. Since the weekly plates are exposed at mid water level, we deter- mined the relative frequency of set at different levels in our area. Figijre 5 shows the percentage of the total set which occurs at one foot internals below mean low water. The first series, held on a fixed rack, shows approximatelj' one per cent of the set occurring at the surface and nearly 80 per cent confined to the k ~ "J foot levels. We repeated this work using a floating rack which fluctuated with the tide and obtained very similar results. The slight variations in numbers setting on the lower plates in the second series are of no real significance. In the third series, we extended the rack so the last plate was a scant inch above the bottom. This experiment shovred a very different picture as to the location of the oyster set. Tjearly 50 per cent of the set was on the bottom plate. The disparity between our data and reports in the literature led us to repeat some of the experiments first repc>rted by A. E. Hopkins in his work on the Olympia oyster in 1935" Figure 6 shows the incidence of set on plates held at different angles in the water. These plates were in separate racks but exposed simijltaneoiasly for 7 day periods. Again, as on our other plates, we fooind the majority, 78 per cent^ setting on upper surfaces (l35 plus l8o^) and only 18 per cent on lower surfaces. These data wei-e difficult to reconcile with Hopkins ' resiilts which are shown on the third line of the table. More than 86 per cent of the Olympic oyster set occurs on under surfaces and less than one-half per cent on the upper surface. -97" ^^sJiw- 'i'Jxi-tS^m^^ Fig. 2. Weighted wood rack with four inch square asbestos cement board plates. Each plate surface provides 100 cm^ area for attach- ment of sedentai'y organisms . 98 ♦ Fig. 3. Photograph of rack carrying white, transpajrent, and "black plates 1^ meters below water surface. 99 OYSTER SPATFALL SELECTION OF SURFACE 4 - YEAR AVERAGE DAILY INCIDENCE % UNDER ! UPPER I » OYSTER 36»4 64»4 BARNACLE 57«5 DARK LIGHT UNDER UPPER BOTH 40 60 26 43 57 74 Fig. k. Percentage of oysters and barnacles setting on upper and under surfaces of cement board plates throughout spawning season for four years. Data include approximately 70,000 oysters and twice as many barnacles. Daily incidence of setting shows percentage of oysters found on upper and under plates exposed for 8 hour periods of continuoiis darkness or light. 100 OYSTER SPATFALL AT' DIFFERENT LEVELS MLW -r 2 1 ' 1 3 4 5 6 7 1 8 9 DTTOM 10 RIGID 20 10 20 FLOATING 10 RIGID 30 50 % 180' 0° 84 16 78 22 43 57 A5 96.5 Fig. 5. Percentage of oysters setting on both surfaces of horizontal plates held in rack at one foot intervals . Racks were fastened to wharf (rigid) or suspended from float which fluctuated with the tide. Ratios show percentage of oysters setting on upper (l80°) and under surfaces. Last ratio in- dicates plate at 9 foot level. 101 OYSTER SPATFALL ANGLE OF INCIDENCE-% 49-\ 90* 4 135V IfiO* C* 0' 45 90 A 135 180 SUSPENDED 8 10 4 41 37 ON BOTTOM 96 6 3.4 ON BOTTOM 86 13 ,7 2 .1" SUSPENDED 705 15.5 5.5 i 1 6 2 Fig. 6. Percentage of oysters setting on cement board plates held at several angles. Data include approximately 6,000 oysters. Tabulation compares results obtained at Pensacola (first two series) with results obtained by other investigators. 102 We find the ans-wer to these apparently conflicting results ty referring again briefly to Figure ^'c As noted earlier, 50 per cent of the set in the third series occurs on the tiottom plate, out more slgnl- ^ ficantly, 96 per cent of these are on the upper surface of the bottom fjB plate, jrjj all of tne remaining plates, the majority of the set occurs on the uMer sijrfaces. The ratio of top to bottom set for each series is shown in the lower part of the figure » The last ratio is that of the tottom plate of the third series.. If we examine Figure 6 again, we find reasonably good agreement between my plates and Hopkins' plates which were located on the bottom. The final line in the ta'Dle indica.tes the data obtained by a third in- vestigator using frosted glass plates suspended above the bottom. These data Include all bivalves but were primarily oysters. The results are in good agreement with Hopkins ' but are almost the exact opposite of my own data shown on the first line of the table. This was especially in- teresting to me, since Dr, Pomerat did this work at Pensacola in 19^0, We repeated his experiment as closely as possible, using the same locations and, perhaps, some of the identical glass plates which he used, but are unable to confirm his observations = Since our results have been consistent over the past three seasons, I conclude that some special hydrographic feat^ure was present during the two weeks that he conducted his experiment. Possibly in 19^0 excessive turbidity caiosed a rapid sedimentation of his plates preventing bivalves from setting on the upper surfaces » Figure 7 shows one of the special crate collectors used to com- pare spatfall here with other areas where crate collectors have been testedo Each ciibicle of the crate measures approximately 2 x 2 x ^ inches. We find this type of cultch expecially efficient in attracting oyster spat, as many other investigators have reported, I have tabulated the actual numbers of spat co\inted in a single test. The uniformity of these num- bers, depending on the angle of surface, is extremely interesting, v'ar- ious organisms covered only about 10 per cent of the surfaces of the plates and hence there was very little competition for attachment space. The fact that each section xn tne crate caught nearly identical numbers of oysters indicates to me an unexpectedly uniform dispersion of larvae in the plankton. The percentages of oysters found on the different sur'- faces of all of these collectors agree with results obtained on plates^ held singly and in series, Fr'om these ana other experiments I gain a general plct-uj-e of the behavior of oyster lar"Va,e at the setting stage in the Perisacola area. The greatest deterrent to setting is a layer of sediment, j"'ust as in other areas investigated, A deposit of silt only as deep as the larvae, about 1/75 of an inch, will prevent their attachment on what is normally a preferred surface and cause them to set on a surface they would ordinar- ily avoid. The lar'vae have no particular attraction for black or white "103- OYSTER SPATFALL - CRATE COLLECTOR 4 B T D C c NUMBER ON ONE CR*TE A - 20 e - 19 C - 25S D - 32 T - 326 27 19 - 2sr 31 - 334 PERCENTAGE BY ANGLE OF SURFACE EXPERIMENTAL - CONTROL 0* 6 2 90* 16 I 180' 7 8 7 Fig. 7« Photograph of cement board "crate collector" and tabulation of setting on inner s\irfaces of the ten cubicles. Lettered diagram designates surface positions j T - t indicates sum of all surfaces in each vertical row of cubicles. Collectors were suspended at mid depth in three meters of vater for seven day periods. Data include approxi- mately 5^000 oysters. 104 ■backgrounds either In t'ne dark or dsylight hoars, and when above the "bottom have little pj:eference to the lighted or anlighted side of a plate » I find no evidence that phototajfls plays a part in their selection of cultcho In one limited series of experiments, the lax^ae set primarily during the daylight hours » They appear to set equally on the rising and falling tides as well as dircing slack wa.ter pexiodso This may 'be a special condition of the Gxilf environment, where there is only one tide each day and the change m water level is slight. We can predict the location of the spat, other conditions being comparatle, almost entirely on the tasis of the larvae's struggle against the laws of gr-avity. The majority are located and set on the bottom and their numbers decrease as the distance from the bottom increases. As the larvae swim upwar'ds through the water they are just as likely to hit and set on an -under surface as, when they fall back down through the water, they may Mt and set on an upper siirface. I believe there is no relation bwtween the swimming position of the larvae, i.e. with _ its foot upwards, and the surface on which the larva, attaches. There ar-e two factors of prime importance in determining the utilization of a surface as ciiltch. Sediment physically interferes with setting on upper surfaces; this factor increases in importance near the bottom where currents that might wash silt away are relatively weaJc^ The second factor of importance is the occur-rence of barnacles » Bax-nacles may set more quickly than oystei's on newly exposed cultch and the sweeping action of their appendages in collecting food repek the laivae. On upper surfaces, this sweeping action does not interfere too much with larvae which drift down between the barnacles and set. On vertical and tinder surfaces, however, when an oyster larva comes into contact with this field of activity it closes and fallB awsy from the surfaeeo Relative- ly few bai-nacles can seriously interfere with the setting rates on vertical and under surfaces . In all of our work we have found that deviations from the expected 1;1 ratio of spat on upper and under sur- faces can be correlated with the numbers of barnacles on the under side. Barnacles have a marked preference for settirig on under surfaces, and this leads to the predominance of the oyster set on upper sui'faces in this areao The importance of barnacles is obscured or overshadowed on bottom cultch where siltation is of paramount importance^ In Bummarizing this work, it appears that in this area the move- ment of mature larvae is governed almost entlr-eiy by the laws of chance and gravity, Tiie only selectivity larvae show in setting results from their avoiding silt or' other organisms and they will be found on the first clean s^orfaee they can reach regar-dless of its position in the water o It should be noted that these data refer to the incidence of setting and not spat survival., In some areas, factors causing early mortalities operate at certain levels or positions « This condition may produce an erroneous picture of the original location of the spatfall. ■105- THE TIDAL SPAT TRAP, A NEW METHOD FOR COLLECTING SEED CLAMS John Bo Glude U. S. Fish and Wildlife Sex'vice, Boothbay Harbor, Maine The Fish and Wildlife Seirvice was directed by Congress in 19^8 to determine the causes of the decline of soft and hard-shell clams along the Atlantic Coast, and to develop methods for increasing pro- duction. Our initial approach was to accept, for the time being, the statements that a scarcity existed and to attempt the most logical method for increasing production, viz., clam fanning. Clam farming is a well established practice in a number of parts of the world and it seemed reasonable that methods which had been used in other places might be applied to the New England Coast. For many years the Japanese have utilized the tidal flats in Tokyo Bay for the production of clams as a farming venture (Glude, 19^7)- This industry is based on the collection of seed clams from the flats at the mouths of several rivers and the transplanting of these clams to private grounds. After a growing period of about one year the clams are dug and sent to market. Another commercial clam farm exists in Puget So\md, Washington, where one concern has title to approximately 10 miles of beach. Re- production appears to be adequate on these flats and the entire farm- ing procedure depends on natural seeding of the flats . In this case clam farming approximates the management of forestry land where it is simply a matter of harvesting a crop as it comes along and then leav- ing the area until a new crop has reached commercial size- The third area where commercial clam farming is practiced is the eastern shore of Virginia. (Tiller, Glude, Stringer, 1952). Here small hard-shell clams are placed on private beds, protected from pre- datory fish, and marketed when they have attained sufficient growth and when economic conditions are favorable. In each of these clam farming ventures the primary requirement is a source of seed. There- fore, we have devoted a considerable amount of our effort to a search for a source of juvenile clams. We recognize tnree principal methods of obtaining seed clams. 1) Collection of juveniles which have naturally set in large numbers , 2) Artificial propagation, 3) Collecting spat or juvenile clams by some device. -106- Katural setting appears to ce the most practical method for the collection of soft-shell clams. We have found one place in Maine where each year soft-shell clams ^ l/2 to 1 inch in length are foimd in concentrations of 1^000 to 1,200 per square foot over a consider- able area of sandy beach. We have developed methods for collecting these small clams by sorting them from the sand using a hydraulic seed rake (Olude, Spear, Wallace, 1952). Young hard-sliell clams, on the other hand, are seldom found in heavy concentrations. Ordinarily our bottom samples in Rhode Island contain one to 20 per square foot and it is difficult to work out mechanical methods for removing clams when they occur in these low concentrations. Only once in Rhode Island have we found hard clams in concentrations which might be usable as a seed source. This in- stance occurred in Greenwich Bay in the summer of 1951 when some of our samples contained as many as 600 Venus per square foot. This, however, appeared to be a very \inusual instance and could not be de- pended upon as a source of seed quahaugs for a commercial farming venture. The best natural source of juvenile hard shell clams which we have seen is in Casco Bay, Maine. The Maine Department of Sea and Shore Fisheries is now transplanting these overcrowded and stunted clams to deeper waters where they will grow faster and where they will be protected from freezing (Dow and Wallace, 195l) ■> These clams set during recent years when temperatui^es have been high. A cold cycle plight prevent Venus from reproducing in Maine. Therefore, we consider natur-al setting as a sporadic source of seed which should be utilized when available, but which can not be depended on each year. Artificial propagation has long been the goal of both oyster and clam biologists . Reliable methods for propagating Venus have now been developed by Dr, Loosanoff and have been applied in several laboratories. Hard-shell clams, fortunately, are among the easier bivalves to reex and this method may some day be usable on a com- mercial scale. It is entirely possible to rear soft-shell clams in a hatchery, but since they are so often available from natiiral setting it would probably be more economical to \:ise this soujrce of seed rather than ai-tificial propagation. The third method of collecting seed is that of employing some device or proced^ore to induce setting or of collecting the young juve- nile clams. In the oyster industry this would include spreading shells on the bottom to catch the set. In Japan, it might consist of hanging fibre mats out in the water to which the young larvae of some of the clams would attach. We have tried a great number of methods of in- ducing setting, some of which have been successful and most of which have failed. A timely suggestion from Roger Munsey, who was then -107- President of the Massachusetts Shellfish Officers' Association, led us to design an automatic filtering device which we have named the Tidal Spat Trap. ,, The Tidal Spat Irap is simply a "box which fills and empties with the tide and a system of check valves to force the outgoing water through a sand filter. The "bivalve larvae are carried into the "box "by the incoming tide and are kept there "by a tray of sand which filters the water on its way out. The outlet is located a"bout eight inches a"bove the filter so the larvae and spat can remain in water even though the tide falls "below this level™ Figure 1 is a diagram of the operating principle of this device. =108- < I- < Q_ < >- < q: I- q: UJ UJ Q CD m UJ I o I- < > z z < UJ > UJ UJ o X •H ft P W lH • EH •H 0) IX, ^ o u. I o -J Ul o o 109 Resul.ts , ig^B The first Tidal Spat Trap was installed at Soothbay Har'bor, Maine in May, 19?3> to test its operation- Tatle I shows the number of bivalves caught in the sand filter during the first month.. The trap caught over 10,000 bivalves per square foot of sand filter in the first 2U days. Of these, nearly a thousand were soft-snell clams. The ratio of mussels to soft-ihell clams was about what we expected from plankton samples -> Table I: Catch of Bivalves per Square I'oot of Sand Filter, Mark I Tidal Spat Trap, Boothbay Harbor, Maine 1953 Soft Total Date No Days Clams Bivalves May 26 Trap installed. June h 8 __- 2,000 Jtme 12 16 6kQ 6,372 June 18 PP 952 10,639 June 18 Sand filter changed. Jtme 19 1 73 1,171 On June 22 we transferred the spat trap from Boothbay Harbor to Robinhood Cove and attached it to the side of an old sailing ship which had been beached there. This location proved to be less suitable than the wharf at the Boothbay Harbor Laboratory besa'use of the large amount of silt in the water which tended to plug the sand filter. In spite of the plugging by silt, the trap continued to catch bivalve lar- vae in fairly good ntmibers as long as they were present in the water. The sand filters were taken from the spat trap at intervals and placed in running water at the laboratory. Periodically, the number of juvenile clams and mtissels In tnese trays were cheeked. We fotmd that nearly all of the mussels died after they were brought to the laboratory; whereas, many of the clams survived. By October the soft clams present ■HO- in the tanks ranged from 2 to 9 millimeters in length which we con- sidered very good growth in comparison with naturally set juvenile clams. The spat trap was also tried as a plankton collector "by re- placing the sand filter with a plankton net tray made from Wo. l8 triple extra heavy plankton netting. This proved to be quite success- ful in straining 'bivalve larvae from the water until the plankton net plugged. We found that the net would filter successfully for about two days which would represent foiir tides or about 700 gallons of water. It appears that the spat trap might be useful in some places as an intermittent plankton sampler since it filters all of the water which is taken during each incoming tide- -111- Res-'xLts, l9-:>h During the wliiter; two additional spst traps were designed ard built. The Mark II, or yialne model, is 2 feet square and 10 feet tall, to accommodate tidal ranges of 8 to 10 feet. The Mark III, or Rhode Island model, is 5 feet high and has a cross section of 2 feet by k feet. This trsp is deaigned for tidal ranges ot h to ^ feet. In June, 19!^^ ? the tm-ee spat traps were put into operation^ The Mark I, or original model, was placed st Loves Cove on Southport Island, Maine which is the area where we are now conducting most of our plankton studies concer:::iing soft-shell clams « The Mark 11 spat trap was installed in Orr's Cove, Maine, which contains a large popu- lation of hai'd-shell clams and is noted for its heavy sets. This cove was chosen as a tj'pical area in Maine where hard-shell clams are found. The Mark ill spat trap was installed at wickford, Rhode Island, on June 2, 19?^^ and placed in operation the following day,. Mechanical difficulties with the cheek valves prevented its successful operation until June 10. Following this time the check valves and filters operat- ed successfully and Vija, Venus , and Mytilus larvae began to appear in the samples which were taken -112- Table II: Catch of Bivalves per Square Foot of Sand Filter. Mark I Tidal Spat Trap, Loves Cove, Maine, 195^. Total Date Wo Days Soft Clams Bivalves June 10 Trap installed. July 2 22 93 162 July 7 27 139 789 July 9 29 k6k 1,995 July 9 Sand filter changed. July 12 3 1+18 627 The hest catch to date of the Mark II trap at Orr's Cove was during the period of July I5 to 19. In these four days each square foot of filter caught 1,g4U Venus larvae and spat. The total catch of bivalves was 2,396 per sq\;iare foot. The location of this trap appears to be very favorable since a strong current flows past it during the flooding tide. The Mark III spat trap at Wickford, Rhode Island, has twice the filter area of the Mark I and Mark II traps. Therefore catches of spat per square foot of filter are expected to be lower. Best res\ilts to date were obtained during the week before July 19 when each square foot of filter caught a total of 5,296 larvae of which 656 were Venus . At this time plankton coimts averaged 172 Venus per hundred gallons of water. From July 19-22 the Wickford trap caught only k& Venus per square foot of filter, but plankton samples averaged only 6 per hundred gallons during this period. It appears that the spat trap catches follow closely the abundance of larvae in the water. -113- Conclusions 1. The principles involved in the design of the Tidal Spat Traps eire sound. 2. Mechanical difficulties have been overcome. The only moving parts of the spat trap are the two check valves which have "been found to operate satisfactorily. The sand filter retains larvae and spat and allows the water to pass through. ?fo outside power source is required. 3. The results depend on the location, time, and presence of advanced or mature larvae. The location in Orr's Cove appears to be satisfactory; whereas, the location of the Mark I trap in Rohinhood Cove last year was unsatisfactory because of the silt and sediment in the water. The Loves Cove spat trap this year may not be in the best location possible since it is in a cove where there is little circulat- ion of water. The maximum catches indicate that this device may have commercial potentialities for hard-shell clams. h. Methods for holding the seed until it grows to a size when it can resist predators are now needed. This is the next project. We have tried holding the spat in the laboratory at Boothbay Harbor but have found that we would have insufficient room although the growth and survival appear to be satisfactory. Perhaps screened or fenced plots could be developed where the seed could be planted until it had reached a sufficient size. It may also be possible to find certain areas which are free from predators. Growth plots co-'old be established in such areas and the seed transplanted to their final grounds after they had reached a large enough size to resist predators. 5. We can visiialize several applications of the TidaJ. Spat Trap when the details of its operation are perfected. It could be used in Rhode Island to obtain seed which could be planted along the Maine Coast during cold cycles when there was no natural reproduction in Maine. The spat traps might also supply seed for private hard clam fajrms. Biologists could use this as a research tool for evaluating the success of setting or for determining the amount of plankton in the water . 6- This description has been presented as a report on an applied research project which is now in progress. A complete evaluation of the Tidal Spat Trap will be given when the present tests are completed. ■lU- Literatiire Jited Dow, R. L., and D. So WaJ-lace, 1951» A method for reducing wintei mortalities of qua'iiogs ( 7en'us mercenaria'' in Ivlaiue waters^ Maine Dept. Sea db Shore Fish. .Res» 3ujJ..c Ko. k'. 32 pp» Glude, J. B. 19^T» Otiservations on the JapanesS clam fisheries. Washo Sta„ Dept, Fish. Ann. Bull,, NOc hj: 34"ii-3. Glude, J., Ho Spear, and Do Wallace o 1952, The hydjr'a-olic clam rake, a new method for gathering seed clams. Nato Shell= fisheries Assoc. Conv. Add. 1952; 163-I660 Tiller, R. E,, J. B. Glude, and L. D. Stringer. 1952, Hard clam fishery of the Atlantic coast. Comm. Fish. Rev. lit(lO): l-25< .115- RECENT ADVMCES IN THE STUDIES OF THE; STRUCTtJRE AM) FORL'IATIOW OF THE SHEIi OF CRASSOSTREA YIRGINICA Paul S. Galtsoff Fish and Wildlife Service, Woods Hole^ Massachusetts Knowledge of the structure and formation of an oyster shell has not advanced far enough to enahle us to give a complete story of this complex and extremely interesting problem. Like many other marine in- vertebrates, oysters extract calcium salts from sea water and deposit it in their shells. In this way millions of tons of calcium salts are taken annually from sea water and deposited in the living bodies of the animals. After their death they accumulate on the bottom. The calcareous material is partially redissolved, though the process is slow, depending on local conditions, chemical composition of shell' material, and the amount of carbon dioxide in sea water. Oysters play an important role in the calcium cycle since their shells constitute about 90 percent of their total weight. Deposition and accumulati^on of calcareous sediments are the problems of great interest to oceanographers and geologists. The marine biologist, however, is concerned primarily with the biochemical reactions and morphogenetical processes which control the formation of shells. In recent years this problem has attracted the attention of a number of investigators who materially contributed to the understand- ing of the physiology of calcification and shell formation in mollusks. Microscopic studies of the sections of an oyster shell show the presence of three distinct elements; (a) a very thin and poorly developed horny layer called periostracum. Its presence in the oyster can be detected on a cross section of the mantle edge, or by examining the edge of the mantle of a living mollusk; (b) £ prismatic layer con= sistlng of a series of calcite crystals arranged In a honeycomb pattern (Fig. 1). In Crassostrea virginica this layer is well developed only in the right valve; and (c) a calcite-ostracum layer which comprises the greatest part of the shell material. It has a foliated structure made of flat sheets of calcite arranged either horlzo/itally or at an angle to the surface of the shell. In many specimens of Crassostrea virginica , £. gigas , and Ostrea ed-olis , the struct\jre of the shell is complicated by the pre- sence of irregular masses of soft and porous material (known, as chalky deposits) embedded between the layers of hard material. They consist of loosely packed minute crystals of calcite. In exceptional CELSes, the chalky material covers the entire inner surface of the shell but it may be completely absent. About 50 percent of New England oysters in my collection were free of chalky deposits. In the other half the deposits occupied only a part of the shell surface. -116- Fig. 1. Prismatic layer at the edge of a growing shell of Crassostrea virginica. Whole mount x 250. Woods Hole, Mass. 117 Calciim salts of shell can be easily dissolved in dilute mineral acids ox in chelatxng agents such as sodium verEenate, The insoluble residue appeals in the form of thin, homogenoiiB sheets of organic material kept together like pages of a "book. This sub- stance, discovered in I855 by Fr^emy, is known as conchiolin. It is a scleroproteln, the stjucttiral formula of which has not yet been determined. The elementary composition of conchiolin of Gstrea edulls , according to Schloss'herger (1856), is as follows 2 E, 6,5%; C, 50,7^; W, l6»7^o Wetzel (1900) found that conchiolin contains 0,75 percent of sulfur and Halliburton (quoted from Schmidt, I928) gives the follow- ing formula; C^q, H^q, N^, 0^-^. The calcareouji material of mollusk shells is laid either as aragonite or calciteo The shells of edible oysters consist exclusively of calclte; on the other hand, the nacreous layer of the pearl oyster consists of aragonite. Taking adi^-antage of the fact that both calclte and aragonite ate present in the two distinct layers of shell of the fan oyster ( Pinna ) and of the pearl oyster ( Pinctada ) , the French in= vestigators (Roche, Pans on, Eysserlc-Lafon, 1951) attempted to find whether there is a difference in the organic material of the two layers of the same species » They found a distinct difference in the percentage of the two amino acids olDtained from the conchiolin of the prismatic layer i. calclte) and of the nacreous part (aragonite) of these molluskSo In the fir-st one the content of tyrosine (ll.6-17<.0^) and of glycocolle (25"36%; was much higher than in the latter (tyrosine 2.Q~6,0'f; glycocolle 1^1,9-20=8^; , Conchiolin from the shells of Gstrea edulls was found to contain 3»2 percent tyrosine and 15-7 percent glycocolle. ^The content of other amino acids found in the shell of 0, edulls , namely, arginlne. Lysine, leucine, valine and methionine varied between 0.^5 and 3»55 percent. These findings are interesting, but at present pro- vide no clue concerning the role of various amino acids in determining the mlnerological type of shell structure = To the naked eye and under the ordinary microscope the con- chiolin appears as amorphoiis, viscous, and transpar'ent material, which hardens shortly after being deposited. By using electron microscope technique, Florkin of Liege University and his associates (Gregoire, Duchateau, and Florkin, 19?0) have shown that the conchiolin of gastro- pods and lamellibranchs consist of a material laid as a fine network with many meshes of irx-egular shape and variable dimensions , Tnls can te clearly seen in tne photogr'aph of conchiolin of abalone ( Haliotls tuberculata i at magnification of 100,000 times, (Fig. 2), It is ob- vious that the organic membranes of molluscan shells have rather com- plex structures which can be seen only with very Mgh magnification. It is too early yet to speculate regarding the significance of this structure and its role in calcification. The question of the amount of conchiolin in the oyster shell was studied by several investigators. As early as 1817 Brandes and -118= Fig. 2. Conchlolln sheet of the shell of abalone ( Haliotls tuberculata) photographed after decalcification and ultra-sonic treatment. Elec- tron microscope; phosphotungtic acid x 100,000. Courtesy of Dr. Ch. Gregoire, University of Liege, Belgium 1. 119 Bucholz estimated that the entire oyster shell consists of about 98.6 percent CaCO^ and O.5 percent organic materials Schlossberger (1856) found 6,3 percent of organic matter in the prismatic layer of the oyster shell, but only from 0.8 to 2.2 percent in the ealcite ostracum. According to Douville (1936), the albuminoid content of oyster shell is k.8 percent. Determinations made for Korringa (1951) by Dr. A. Grijns gave similar results. It is interesting to note that in the latter tests the conchiolin content of the prismatic layer varied from 3'^ to U,5 percent against the 0.5-0.6 percent in the ealcite ostracum. My own observations made this year on Crassostrea virginica from Cape Cod, Narragansett Ba,y, and Long Island Sound show that in the 3^ samples studied, the organic content of the ealcite ostracum la"yer varied from 0.46 to 1.1 percent. There was no significant difference between the organic content of chalky deposits or the hard portions of ealcite- Duplicate and triplicate tests of the hard portions of shell of the same specimen show that the conchiolin content is fairly constant, the difference not exceeding 0.2 percent. Among the diff- erent specimens, the conchiolin content of the entire shell, varied from 0.3 to 1.1 percent. The presence of chalky deposits and their structure was sub- ject to many speculations. Orton and Amirthalingam(l927) advanced a theory that chalky deposits occur in places where the mantle epi- thelium looses contacts with the shell. This theory received support from Ranson ( 1939-^1) who, without making any additional study, stated that chalky deposits are formed wherever there is a local detachment of the mantle from the shell. Korringa finds no difference in the percentage of chalky deposits in the oysters placed with the cupped valves uppermost and in those which are kept in their normal position with cupped valves undermost. He assumes that the topmost mantle epitheli^jm of the exhalant chamber "is certainly liable to sagging". My observations on Crassostrea virginica show that the mantle epi- thelium adheres rather strongly to the inner sides of the valves and does not sag unless the mantle is pushed down by force. To determine whether local detachment of the mantle from the inner surface of the shell expedites the formation of shalky deposits, I made the following experiments; Small pieces of thin plastic, about 1 cm. 2 J were bent in the shape of shallow cups and introduced between the mantle and the shell. In five oysters the concave side of the cup was facing the mantle, in another five the position of the cup was re- versed, i.e., its concave side faced the shell. Oysters were kept for 55 days in running sea water in the laboratory. During this time they fed actively and there was considerable shell growth along the margin of the valves. After removal from the shells, the plastic cups were found to be covered with hard ealcite deposit. There was not the slightest indication of the formation of chalky material. On the =120- other hand, conspicous chalky areas v/ere formed along the marginal area of shell growth in places where the two valves were in close contact with each other (Fig. 3)- It is clear from these ohser>/ations that chalky deposits may he constructed "by the mantle at any place on the surface of the shell and that the detachment of the mantle epitheliimi from the inner surface of the valve is not a factor in their formation. Korringa (l95l) advances a theory that "chalky material is used by the oyster a-s a measure of economy and as a "^eheap padding' in smoothing out the shell's Interior and in creating the right shell shape to maintain its efficiency of function. The more the oyster shell attains a cupped shape, the more layers of 'chalky' material are deposited 'beyond the muscle to maintain the proper shell dimensions." He emphasizes the significance of the presence of chalky deposits be- yond the muscle scar and for reasons which he fails to explain disre- gards their presence in the other areas. The theory goes far beyond the experimentaLl evidence and its teleological approach does not con- tribute to the understanding of the problem. Since so much emphasis was placed on the significance of chalky deposits in the area beyond the m.uscle scar, it was of interest to determine whether there is a definite tendency in the formation of chalky deposits in different parts of the shell. For this purpose the surface of the valve was arbitrarily divided into the four quad- rants shown in Figure h^ Examination of several hujidred oyster shells of Crassostrea virginica from various parts of the Atlantic Coast show- ed that chalky deposits were absent in 53.1 pei" cent of right valves and 47.9 per cent of the left valves. To have some idea of the extent of chalky deposits present, the following categories were established: I. from 1 to 25^ of the area of a quadrant covered by chalky deposits; II." from 26 to 50/0,; III., from 51 to 75^; and IV. from 76 to 100^. The results, given in Table I, show that the majority of oysters- in which chalky deposits of any size were found had less than 25 per cent of the total shell area covered with them. Table I, Occurrence and Extent of Areas of Chalky Deposits in Crassostrea virginica (percentages); Exclusive of Oysters without Chalky Deposits Percent of shell surface occupied by chalky deposits 0/0 1 -25/0 26—50^ 51- -75/0 76- -100^ Left valve 47.9 25.9 13.6 9.8 2.8 Right valve 53-1 2i+.9 12.0 8.U 1.5 -121- Fig. 3' Chalky deposits (white areas) at the edge of a rapidly growing shell of Crassostrea virginica and near the muscle scar. Woods Hole. 122 Fig. k. Four quadrants of the shell area used in a study of the occurrence of chalky deposit in the values of adult Crassostrea virginica. 125 Chalky deposits of any size were almost uniformly distributed^ k8 per cent occurring on the dorsal half (above the muscle scar) and 52 per cent on the ventral half of the shell. The percentage of occurrence among the four quadrants (A, B, C, D) was also rather uni- form as can be seen from Table 11= Table II. Occiirrence of Chalky Deposits in the Foi.ir Quadrants of the Shell (percentages) Areas A B C " D Left valve 22,2 25-5 29-8 22.5 Right valve 2^.2 23. 22.9 28.8 Although there seems to be an equal chance for a chalky deposit of small or medium size to be fo\ind in any of the four quadrants of the shell, large deposits covering more than three quarters of the area of a quadrant are more frequently found in the dorsal half of the valves (quadrants A and B, Table III.) Table III. Frequency of Occurrence of Large Areas of Chalky Deposits (Category TV) within the Four Quadrants of the Valves (percentages) Areas of the valves A B C D Percentage occurrence 33.3 1+7.3 10.8 8.6 (both valves) Studies of the distribution of chalky deposits in Crassostrea virginica do not support Korringa's suggestion that they are purposely formed by the oyster in order to maintain a constant distance between the shells in the posterior area opposite the exhalant chamber. It is well known that the valves of oysters differ in size and shape, the left valve usually being cupped and heavier than the flat and lighter right valve. Normally the oyster occupies a position with the right (flat) valve uppermost. The majority of Atlantic oysters, when placed on their left valves with the dorsal end away from the observer, show a curvature to the left. This indicates more rapid growth of the shell along the dorso-ventraJ. axis, with a slight shift of the direction of growth to the left. In very young oysters which frequently appear to be round -I2U- this tendency is less pronounced^ Examining my collection of shells^ I foiuid some oysters in whicli the growth along the dorso-^'entral axis was almost equal to the growth along the a;aterio-posterior direction. The width of these specimens was almost equaJ. to their length and sometimes even exceeded it (?ig. 5)^ The growth of shell in any direction is an expression of a metalaolic gradient along the given axis. The latter is not definitely fixed in the oyster "but changes in response to environment. As a rule, oysters living on soft bottom or in very crowded condition on n3.tiaral reefs tend to form long narrow shells while their growth in width is suppressed^ There are, however, other, apparently intrinsic, factors which cause the change in the direction of growth probalDly not associated with environmental condi- tions. In several specimens collected in various parts of the coast the direction of growth shifted from left to right. This can be clear- ly seen in Figure 6 showing the two left shells of the oysters, one normal and the other with a distinct shift to the right. The "right handed" oysters were found in Texas, Chesapeake Bay, Narragansett Bay, 8jid New Hampshire. There was no indication of the presence of any mechanical obstruction that might have interfered with normal growth. In every other respect the "right handed" oysters were normal and had the typically cupped left valves with well developed grooved beaks. The "right handed" specimens are comparable to the so-called inverted shells in which the typically left valve structures appear on the right side and vice versa. Inversion was foimd in several pelecypods (Lamy, 1930). In case of Cr assostrea virginica , the inversion of gi'owth does not affect the morphological structures but is expressed only in the shifting of the axis of growth. There is a difference in the physiology of the right and left valves of the oysters. The rate of calcification is significantly higher on the left side than on the right one. This can be easily noticed by examining the newly formed siiells . The material secreted by the left mantle is thicker and heavier than the material deposited during the same time by the right mantle. For these observations, con- ducted since last April, I iised aduat oysters which had no recently deposited shell areas along the edges of the valves. They were placed in laboratory tanlcs supplied with nonnlng sea water. .About two months later the pieces of the newly deposited shell on each vslve were care- fijlly removed from the shell. After measur'ing their ai'eas vrith plani- meter, they were dried at 55°C. and weighed. The resiilts are sianmajrized in Table IV. -125- Fig. 5' Large Crassostrea virginica , from Hadley Harbor, Naushon Island near Woods Hole. 126 Fig. 6. Two left valves of Crassostrea virginlca from Maine (on the left) and from Texas (on the right) . 127 Table IV. Oysters Areas of New Growth and Rate of Deposition of Shell Material in Milligrams per Day per Squaire Centimeter during April — June, 195^^ Woods Hole, Mass. Area of Weight Ratio lEW shell per L'.R. Valve cmr cm.^ (mg. ) Ratio (mg-) Wimiber of days under observation Five-year old Warraga.nsett Bay Left valve 5.80 156 Right valve 5.16 59.3 Adult Narragansett Bay Left valve 7.1 123 Right valve 7.7 19.9 Adult Narragansett Bay Left valve 6.1 Ik. 2 Right valve 8.8 25.5 Two -year old New Hampshire Left valve 3.68 163.8 Right valve 1+.20 52.0 Old New Hampshire Left valve 6.83 71.2 Right valve 7.35 33-0 2.6 6.2 2.9 3.2 2.8 1.1 1.8 0.3 1.09 0.37 2.98 0.95 1.3 0.6 55 days 68 days 68 days 55 days 55 days 2.2 -128- In every case the aoioimt of calcified material deposited over a unit of area was considerably greater on the left valve than on the right one, the difference varying from 2.2 to 6.2 times. The ratio of calcification along the inner portion of the mantle may Tae studied hy inserting small pieces of plastic or other material of knoTrm area and weigh-c TDetween the mantle and shell. In interpret- ing the results one should conijider, hovever, that the presence of a foreign body may produce pathological conditions which upset the nor- mal rate of calcif Ication^ The results obtained >rith this method show great variability. Observations made with l6 adult oysters at Woods Hole during the period of August 9-20, 1953, show that in 15 specimens the daily rate of shell depositiniip^r square centimeter varied from O.^J- to 2.1 milligrams. One oyster deposited lij-.2 milligrams in two days or 7*1 mg. per day. Data obtained this sj^ring v/ith tne Warragansett Bay oysters kept in laboratory tanks for 68 days during the period of April-Jxme show the variation from 0.1 to 0.79 mg. per day per square centimeter. In one oyster the rate of deposit ^jnder a plastic cup was l6.^ mg. per day„ In some oysters the presence of plastic material produced pathological conditions which resLilted in the formation of leathery capsules similar to the blisters frequently found in the area of the adductor muscle. These experiments are being continued using various techniques designed to minimize the effect of local stimulation of shell secreting tissues. French physiologist Monnigeult (i939) apparently was the first one to point out the role played by phosphatase as a factor in the acceleration of shell formation. This enzjmie is probably an agent in the transfer of calcn.um. Later on, Eevelander and Benjer (l9^8) ap- parently i-Lnaware of Momigault's work arrived at the same concliosion. yreem.aji and Wilber (l9^) have demonstl-ated the presence of another ensjme, carbonic aiihyarase, in the mantle tissues and body fluids of some pelecypods and gastropods o Ifhile this enzyme may be important in shell formation in some species, its negligible activity in other mollusks suggests, however, that shell may be deposited in its absence^ Physiological and histological studies on gi*owth and regenera- tion of shell of the o.^'ster d-isclose the great complexity of the pro- cess. The role played by different parts of the mantle epitheliLim in secreting conchiolin and in depositing calcium carbonate in the form of well arranged prisms of the prismatic layer or as densely packed lamellae of the calcite presents a stimulating problem of research. Observations made in my laboratory on isolated pieces of mantle and on the mantle edge aftei- the removal of a portion of the shell show that clear, viscous, sometimes stringly conchiolin is secreted from the periostracal groove located between the outer (secretory) and the middle (sensory) folds of the mantle. The sensory fold is capable of great extensibility and seems to ser^'/e as a temporary support for the viscous -129- conchiolin iintil the latter hardens. This conclusion is confirmed by the examination of the sections of mantle which clearly show tl^at con- chiolin produced at the mantle edge originates in the periostracal groove. The results are in agreement with the ohservations made by other zoologists on the shells of 0. edulis and Anodonta . Mucus secreted by the mantle of the oyster contains a large number of blood cells- Their role in calcification is not yet under- stood. The newly deposited material contains minute granules which sometimes give a positive reaction for calcium with alizarin and other reagents u^ed for identification of this metal. Unfortunately, none of the available color reactions for the detection of calcium are dependable for they often give negative results . Because of this technical difficulty, it has been impossible to trace the origin of the tiny granules known as calcosphaerites (Fig. 7) which appear in the conchiolin shortly after it is secreted by the mantle. The growth of these crystals and the formation of large crystalline units which eventually form the prismatic layer (Fig. l) can be seen on the black and white enlargements of Kodachrome photographs made with the polariz- ing microscope (Figs. 8 and 9) • In polarized light these crystals of calcite present a pictiire of great brilliance and beauty. The conditions under which the calcium carbonate forms the prisms of the prismatic layer or is deposited as a foliated structirre of the calcite ostracum are not known. The problem presents an oppor- tunity for further research of calcification. In conclusion, I want to remark briefly on the source of calcium used in the formation of the shell of Crassostrea . In 1938^ Robertson and Prentice pointed out that sea water is the source of calcium for building the tubes of an annelid worm, Porno tocero s triqueter . I in- dicated at that time (Galtsoff, 1938) that calcium salts required for the building of the shells of Ostrea ( Crassostrea ) virginica are pro- bably taken directly from the sea water. Experimental work by Jodrey (1953) using Ca^i- clearly shows that pieces of oyster mantle separated from other tissues are able to deposit calcium taken directly from sea water. She also shows that the rate of calcium turnover in the edges of the mantle is about twice as rapid as in the interior of the mantle. The use of radioactive isotopes gives a new tool for solving many pre- sent mysteries connected with the formation, maintenance, and growth of shells of oysters and other marine invertebrates. -130- Fig. 7. Small granules (calcospaerites in con- chiolin shortly after it had been secreted "by the mantle. Black and white enlargement of a Kodachrome photograph taken in polarized light. Highly magnified. 131 " Sff ,4* % €M Fig. 8. Calcite crystals found in conchiol- in 2U-i+8 ho\irs after it had been secreted. Black and white enlargement of a Kodachrome photograph taken in polarized light with the magnification of X 250. 132 Fig. 9« Large calcite crystals at the begin- ning of the formation of the prismatic layer. Black and white enlargement of a Kodachrome photograph taken in polarized light with the magnification of X 250. 133 Litei'ature Cited Bevelander, G., and P. Eenzero 19^8o Calcification in marine molluaks, Biol» Bvill. 9k i I76-I83. Douville, H. 1936'. Le test des lamellibranches : sa formation dans I' Ostrea ed ulis , Compto Rend,, Acad» Sc. Paris 203: 965-968. Freeman, J. Ao, and K. M, Wilbero 19^8, Carbonic anhydrase in molluscs « Biol, Bull„ 9^: 5!;-59» Fremy, E, l855» Reeherches chlmiques sur les oso Ann. de Chimie et Physique, 3r-do Ser, U3 : 1+7-107. Galtsoff, P. S, 1938 » Sources of calcium for shell of Ostrea virginica o Nature l^il: 922 „ Gregoire, Ch,, Ch. Duc'hateau, and M, Florkin. 1950» Structure, etudiee au microscope electronique, de nacres decalcifiees de mollusques- (Gasteropodes, Lamellibranches et Cephalo- podes). Axell» Intern, Physiol, 58t II7-I2O. Jodrey, Louise H, 1953' Studies on shell formation. III. Measure- ment of calcium deposition in shell and calcium turnover in EatntLe tissue using the mantle-shell preparation and Ca -'• Biol. Bullo lOlj-: 398-U070 Korringa, P. 1951 •= On the nature and function of "chalky" deposits in the shell of Ostrea edulis Linnaeus , Proc. Calif. Acad, Sci., 1+th, Ser, 27(5): 133-I58. Lamy, E, 1917° Coquilles senestres chez les Lamelirbranches . Bull, Mus, Wat, d' His to ire Natur-elle 22: U89-I193. Mannigaiilt, P, 1939" Researches on the calcareous materials in mollusks; phosphatase and histochemical precipitation of cal- cium. Ann, Inst, Oceanogr', I8: 331-^26, Orton, J. H, , and C, Amirthalingamo 1927, Notes on she 11 -deposit ions in oysters, Jr. Mar, Biol, Assoc. U,K,, W,S, ikt 935-953. Ranson, G, 1939-^1. Les hultres et le calcaire. I. Formation et structure des "chambres crayEioses", Introduction a la revision du genre Pycnodonta F, de W, B\ill., Mus, Nat. Hist, Nat. Paris (2) lit 1+67-472, 12s 1|26-1|32, 13; U9-66. Roche, Jean, G, Ranson, and M, Eysseric-Lafon, 1951. Sur la com- position des scleroproteines des coquilles des mollusques (conchiolines) . Comptes Rendus d. seances de la Boc, de Biol, 11+5: II+74-II+77, .13'^- Schlossberger, J. I856. Zur nalieren Kenntniss der Miischelschalen, des Byssus imd der Chit inf rage. Armalen Clieni. u. Pharm. 97: 99-120. Schmidt, W. J. I9280 Perlmutter und Perlen nebst elnem Anhang uber Phauenstein. Die Rohstoffe der Tierreichs, heaxusgeg. von F. Pax und W. Arndt 2: 122-l60, Wetzel, G. 190O0 Die organischen Substanzen der Schalen von Mytilus wad Pinna . Hoppe-Seyler 's Zeitschr. f . Physiol o Chem» 29: 386-UlO, ■135- ON THE RATE OF WATER PROPULSION BY THE BAY SCALLOP Walter A. Chipman Fish and Wildlife Service, Beaufort, North Carolina Studies of the movement of sea water through the mantle cavity by lamellihranch molluscs and the efficiency of the gills in removing particulate matter from this flow are of considerable interest to bio- logists concerned with investigations of the feeding activities of these bivalves. Only through a more complete understanding of the factors controlling the rate of water propulsion, the retention of particles by the gills, and the ingestion of filtered material can we approach problems in the nutritional physiology of these animals. The rate of water propulsion of a number of species of lamelli- branchs has been reported by investigators using either direct measure- ment techniques or indirect methods based on the reduction of the num- ber of particles in a suspension in which the animals have been placed. Considerable work has been done on the factors affecting the rate of pumping of oysters using direct measurements of the rate of flow. In many lamellibranchs direct measurements cannot be made and indirect methods have been widely used. Investigators have followed changes brought about by their experimental animals in suspensions of various inert materials and of living plankton cells. For the most part, the observations have been limited to those employing rather dense sus- pensions and to those in which the changes were quite great. With the availability of methods of labeling plankton cellft with radioactive isotopes and the extremely accurate technique of measuring changes in cell numbers based on the detection of small amoiints of radioactivity contained in such cells, it is advantageous to employ these methods in studies of the feeding and filtration rates of filter feeding invertebrates. At the Beaufort laboratory we have employed various species of plankton containing different radioactive elements in studies of the foods and feeding processes of various shellfish. The work which I wish to report today deals with use of radioactive plankton in the measurement of the rate of water pro- pulsion by the bay scallop, Pecten irradians Lamarck. Methods Observations were made on single scallops immersed in suspensions of plankton cells in sea water. The suspensions were always very ade- quately stirred. The volume of suspension used was varied for the size of the scallop immersed so as to allow satisfactory measurements of the decrease in suspended plankton cells within convenient measuring in- tervals and during satisfactory experimental times. -136- The plankton species to be used were grown in such manner as to give rather dense cultiires of rapidly dividing cells containing the desired amount of radioactivityo The cell population was measured using a haemocsr-tometer and the radioactivity of a known u^jmber measured. By dilution of the culture, a suspension of the desired concentration was prepared. Knowing the radioactivity per cell, clianges in the num- ber of cells in the suspension were easily and very acciirately follow- ed by radioactivity measurements of small aliquots of the suspension. Tests were made to make certain that the radioactivity was due to the isotope within the cell and not to its presence in the water. In earlier work the cells of the aliquot were destroyed by acid and the radioactivity of the liquid measiired. We now find it more convenient to filter the cells onto a millipore filter and to ascertain the radioactivity of the cells of the aliquot directly on the filter. Results On being immersed in an experimental phytoplankton siispension, the scallops opened almost immediately and soon started to filter the water through their gills. This resulted in a lowering of the cell content of the suspension. A semilogarithmic plot of the cell con- centrations measured at frequent intervals throughout the period of observation was made to visualize these changes. The rate of clear- ing varied, but followed the same pattern in nearly all of the tests. If one assumes that the conditions of the experimental arrange- ment were satisfactory, the straight line decrease in the logarithm of the cell concentration with time fits the mathematical equation for a constant rate of water filtration with complete removal of the sus- pended phjrtoplankton from the water filtered by the scallop. During this time of complete removal, the observed rate of decreeise in cell concentration may represent the rate of water filtration of the scallop. Changes in the rate of clearing of the siospension can be interpreted as resiilting from changes in the amount of water filtered.. As the observations were continued, the decrease in phytoplankton became less and less. This resiJlted in a flattening of the curves. Actually, the number of cells in suspension gradually increased in instances where the observations were prolonged. There are a number of factors concerned with detennining the rate of reduction of particles in suspensions in which the scallops were immersed. Different ones of these may affect the rate at differ- ent times, or more than one m_ay be acting at one time. The flattening of the curves of our observations, therefore, may not have resulted from a change in the rate of water filtration. ■137" The decrease in rate of removal was apparently related to time in the si^pension» It was not related to cell concentration. Series of observations were made starting the scallops in concentrations at which there was a previoiis leveling off in the rate of removal. In each series there was rapid removal followed by a less rapid rate re- gardless of the starting cell popul.ationo Incomplete mixing of the filtered water with the unf iltered would result in a decrease in the observed rate of phytoplankton re- moval that would get less and less as the observations were continued. Changes in the amount of stirring, however, did not alter the shape of the curves in our experiments. Although it is realized that it is virtually impossible to get the mixing required to fully meet the requirement of the mathematical expression giving a straight line de- crease, we believe that recirculation of filtered water through the scallop before mixing was not wholly responsible for the flattening of the curves. The decrease in the rate of removal refle'cted in the flattening of the curves could be interpreted as a change in the rate of the water propxilsion of the scallop. However, such a change was not apparent. The scallops were seen to be creating a considerable current of water even when there was no appreciable decrease in suspended plankton. It seems not unlikely that the changes in the rate of clearing of the siispension was a result of a changed efficiency in the filtering by the scallop, together with a i-eturn of cells previously entrapped in the mucus of the gills » If one assumes that the scallop was filtering the suspension efficiently with complete removal of the suspended particles, it is possible to calculate the rate of water propulsion by the application of the formula gi,ren by Jorgen&en in 19^3 » ( log eoncp - log concf )M log e ° t Undoubtedly the rates obtained are not absolute. They can only repre- sent an approximation since the original assumption made is not likely to be entirely correct. Escapement of plankton through the gills, if occurring as a fixed percentage of the concentration in the suspension, would not change the nature of the curve but would alter the slope. The measured pumping rate may actually be lower tha,n the true rate. Individual scallops in observations made at different times differed in their rate of filtration, but under like conditions of test the rates were reasonably uniform. The average rates .were the same for experiments using either Nitzschia or Chlamydomonas cells -138- for the suspended material. They did not appear to be related to concentration. As the scallops increased in size, their rate of water filtration increased. In June or early July the small scallops averaged about three liters per hour. Later during the siimmer they filtered increasing amounts as they grew in size. By fall they were pumping an average of nearly 15 liters per hour. The maximum rate observed was 25-^ liters per hour for a scallop measuring 65 milli- meters in length. The average rate of water filtration per gram of tissue was greater for the small scallops than it was for the larger. Summary In conclusion I should say that the use of radioactive plankton cells in studies of the feeding activities of shellfish is particularly valuable. In using such techniques to measure the rate of water filtra- tion by the bay scallop, we have found that the scallop has a high rate of water filtration, probably correlated with its active mode of life. The work reported indicates that the filtering activities and feeding of lamellibranch molluscs have many phases not yet fully understood, but the application of radioisotope techniques offers opportunity to investigate a number of these more easily. ■139- GROWTH STUDIES IN THE QUAHOG VEFJS MER.CEMRIA Alton H. Gustafson Bowdoin College, Brunswick, Maine, and the Maine DepaJTtment of Sea and Shore Fisheries Introduction Venus mercenajria , the quahog or hard-shell clam, is a bivalve mollusc of considerable commercial importance widely distributed along the Atlantic coast. It grows from between the tide levels to depths of at least fifty feet. Br^'unswick, Maine, is the center of commercial digging operations in the state. Here the receding tides expose great areas known as mud flats. Most of the digging is done between the mid tide and low tide levels . Recognizing the need for accurate information about the ecolo- gical factors responsible for the occurrence, distribution, and growth of the organism, the Maine Department of Sea and Shore Fisheries is engaged in a series of studies designed to yield data of value both scientifically and for the promotion of the fishery. The program in- cludes investigations of (a) the early life stages: reproduction, planktonic existence, and setting habits, (b) the fate of the heavy set of 1952 in certain areas, (c) the growth of natural populations, (d) comparative growth studies of popiilations of known sizes planted under differing conditions, and (e) the factors which presumably in- fluence growth. In spite of the abimdance, availability, and commercial im- portance both actual and potential, surprisingly few studies have been made of either the ecology or the growth of the organism. Pub- lished data by Bedding (1912), Chestnux (l952), Haskin (19^9), Kellogg (1903), and Pratt (1953) and unpublished data by Carriker and Kerswill have yielded information of great value. However, they should be re- garded as but the first steps in acquiring the data necessary for either a real understanding of the organism or developing a sound management program for the fishery. In Maine, studies by Dow and Wallace (1951) on winter mortalities and some aspects of growth have pointed up the scarcity of our knowledge of the factors of importance in growth and survival. The material here presented is in the nature of a preliminary and progress report. It deals chiefly with a comparison of growth of populations of several sizes planted under differing conditions in several localities, an analysis of the annual increment, and some comparisons with conditions reported In other geographic areas. -l4o- Methods From time to time huge sets of Venus have occurred in several of our coves and we thxis have "been given an opportunity to obtain specimens of almost any size in any quantity for experimental pur- poses . The specimens are gathered, measured to the nearest milli- meter in length, given an identifying mark with a durable ink, and planted in chosen areas legally closed to digging. They have been planted in bottoms of different types, at various tide levels, and in several concentrations. This report deals with a small fraction of the data accumulated in 1952-53 from plantings of over 13,000 specimens- Comparison of Growth at Simmons Reservation and Avery Cove. At Simmons ' Reservation 200 individuals of each of the following sizes were planted in June, 1952, and harvested exactly one year later, and replanted for further study. Table I shows the pertinent data: Table I Original length Actual increase ^o increase IT 17-0 100 27 18.13 72.5 37 U.85 ii0 57 12.37 22 77 ■ 6.52 8.5 Graph I shows that there is a fairly uniform decrease in the percentage of increment as the initial size increases. From the graph one may make an estimate of the probable growth increment of specimens of any size. For example, 30 millimeter specimens might be expected to show a 60 per cent increase in size in a year or to add 18 millimeters in the year. Table II and Graph II show the results of a similar planting at Avery Cove. Unfortunately, vandals removed the larger sizes so we cannot complete the curve. It would have been interesting to be able to determine whether or not the curve changed in a manner similajr to that shown for Simmons. It is evident that growth is not as great "in Avery as at Simmons. .141. 00 ,(100) 90 80 70 GRAPH VENUS MERCENARIA GROWTH IN SIMMONS' RESERVATION, FREEPORT, MAINE. JUNE, 1952- JUNE, 1953 60 UJ 'to find the meat of a dead clam, Venus mercenaria , infected with a D. marinum-like fungus. During the fall and winter of 1953-5^;, 12 of l6~species of bivalve mollusks collected near Gloucester Point, Virginia, were fo'ond infected with similar fungi (Table l) . None of the fun_gu£ parasites has been identified except the one causing a mycosis in oysters.. How ma,ny species of fmigi are in- volved? Can spores from one host species infect individu-als of other species? And of most Inmiediate importance, how many bivalve species will serve as host to the oyster parasite? Very early it was noticed th-at infections in some bivalve mollusks differed from infections in oysters in two ways: (l) In several host species 100 per cent infections have been found for groups of 25 animals. Infections in live oysters have never exceeded 80 per cent. (2) Nearly all infections of bivalve mollusks other than oysters have been "light" whereas most groups of oysters with a high percentage of infection show some "moderate" and "heavy" infections indicating Contribution from the Virginia Fisheries Laboratory, No. 'ph. -157- that the disease is becoming worse in some individuals- The high incidence and low intensity of fungus parasites in certain "bivalve mollusks may indicate greater tolerance by the hosts and a lower level of lethality than exists in oysters. Morphological differences have been noted in the cultured para- sites of various bivalve mollusks but these are not understood at present. Wow hobby has become inextricably entangled with research. Happily, knowledge of bivalve species and their distribution is an asset to studies of fungus parasites of molliisks . Table I Occurrence of Dermocystidium -like Fungi in Bivalve Mollusks Species in which fungus has been found: Mercenaria mercenaria Linne Mya arenaria Linn^ Macoma balthica Linne Macoma phenax Dall Macoma tenta Say Mulinia lateralis Say Anomia s Implex Orbigny Tagelus plebeius Solander Anadara transversa Say Laevicardiimi mortoni Conrad Ens is minor Dall Lyons ia hyalina Conrad Hard-shell Clam Soft-shell Clam Little Roimd Clam Tenta Macoma Dwarf Surf Clam Jingle Shell Stout Tagelus Transverse Ark Morton's Cockle Razor Clam Glassy Lyons ia Species in which fungus has not been found: Solemya velum Say Bankia gouldi Bartsch Volsella demissa Dillwyn Brachidontes recurvus Rafinesque Atlantic Awning Shell Gould's Shipworm Ribbed Mussel Hooked Mussel -158- Note 2. The Disappearance of Fungus Infections in Late Winter and Spring. According to the thioglycoilate test (Ray, 1952), D. niarin\im almost disappears from live oysters in Chesapeake Bay during late winter and spring (March, April, and early May). Based on samples of 25 oysters, the disease apparently disappeared completely by March in oysters that had been 80 per cent infected in November. Despite the apparent absence of the disease in lats spring, oysters which have once had infections develop earlier and greater mortali- ties the following summer than oysters transpls,nted from areas where infections never occur. Also, oysters once i;ifected, but testing negative in late spring, will develop the disease in areas where the fungus is not present o This suggests that latent infections, not detected by the thioglycoilate method, are present in these oysters throughout the winter and spring. Apparently Chesapeake winters may not be quite long and severe enough to eliminate in- fections from all oysters. The possible role of other bivalves as sources of infective material for the oyster disease must not be overlooked. Sketchy records suggest that fungus infections in the other bivalves also disappear in late winter except in Macoma balthica and Anad.ara tran s- versa . Note 3- Racial Differences in Susceptibility to D» marinun. Dermocystidium is a fascinating disease I It resembles a human disease called Blastomycosis in that nearly all organs and tissues are attacked. This makes it easy to study; almost any piece of a dead or live oyster can be cultijred with reasonable ex- pectation of malting a correct diagnosis of infection. Dermocystidivjii is a deadly diseasel Vie are continually as- tounded at its scope. From 80 to 85 per cent of all our dead oysters from trays show serious infections of the fungus. Only yoiing oysters under one year of age escape the disease. Excluding predation and adverse physical conditions such as too much silting, the disease appears to be the dominant cause of oyster deaths in lower Chesapeake Bay and the lower areas of the major tributaries in Virginia. Worst of all for the oystenaan, there is as yet little evidence of resistance to the disease. Six year old oysters in trays at Gloucester Point are still dying at about the same rate and with the same degree of fungus infec-cion as they did. three years ago. -159- One ray of hope came out of last summer's experience with tray grown oysters originating outside Chesapeake Bay. It was noticed that one year old oysters from Seaside of Virginia were dying at a rate comparable to that of older Chesapeake Bay oysters. Deaths among yearlings are usually very light. Furthermore, a tray of two year old oysters from South Carolina was not following the pattern for oysters of that age: mortality was low and fungus infected oysters were few and late in appearing. Thioglyeollate tests of live yearling oysters from South Caro- lina, Chesapeake Bay, and Sea,side of Virginia, all grown in trays at Gloucester Point, revealed that the Seaside oysters were indeed more heavily infected than the others (Table II) . Among two year olds. South Carolina oysters had fewer and lighter infections than Chesa- peake Bay oysters. A firrther comparison of varioiis age oysters from the three sources (Table III) shows that both yearling and three to four year old oysters from Seaside had much higher mortalities than Chesapeake Bay oysters; and South Carolina two year olds had much lower mortality than native oysters. Regardless of age, neaxly all groups from which a considerable number of gapers were recovered showed about 90 per cent infection of the gapers with D. mar i num . Only the South Carolina two year olds deviated from this pattern. Pending the outcome of studies now in progress, it appears that Seaside oysters are more susceptible to the fungus than Chesapeake Bay oysters and South Carolina oysters are more resistant. The fungus is present in South Ca-rolina waters but apparently absent from Seaside and Chincoteague Bay. For commercial oystermen, does this explain repeated failures of Seaside oysters in Chesapeake Bay? Does it signal danger for Sea- side if the fungus is introduced and water conditions are favorable? Would it be wise for oystermen from Seaside and farther north to know the areas in Chesapeake Bay that are infected and the seasons when the disease is rampant? These are questions that we cannot answer, but the disease is already serious in lower Chesapeake Bay and could be- come a problem in more northerly waters . -160- Table II Effects of Source (Race?) and Age on Susceptil)ility of Oysters to D. marinum Incidence in live oysters — September 1953 History Source Number Percentage Weighted tested infected incidence** Yearlings* South Carolina (Tray 28) 50 Chesapeake Bay (Tray 33) 50 10 0.10 0.00 Seaside of Virginia (l^ray 15 ) 25 64 O.J Two-yeax South Carolina old (Tray k) 25 oysters Chesapeake Bay (Tray 11 ) 37 20 35 0.20 0.78 * All moved as spat to Gloucester Point in fall of 1952. ** Weighted incidence combines intensity and incidence of infection by assigning artificial values of for negative, 1 for light, 3 for moderate, and 5 for heavy infections. To get weighted Incidence the sum of all values is divided by the number of oysters tested. These ratings can be compared directly with the six categories assigned integers from to 5 "by Mackin (1951) . Our ratings (ten in all) have been grouped into h categories. -161- Table III Effects of Source (Race?) and Age on Susceptibility of Oysters to D. marinum Incidence in gapers — June to October 1953 History Source Percentage No gapers Percentage Weighted mortality tested infected incidence Yearlings Seaside of Virginia South Carolina (1952) 30.1 31 87.1 3 .'19 (Tray k) 7.1 k 25-0 0.25 Chesapeake Bay (1952) (Trays 11 & 12) 2.7 1 100.0 5.00 Two year South Carolina old (Tray k) 9.3 28 50.0 1A3 oysters Chesapeake Bay (Tray 11 ) 24.5 79 91.0 U.20 (Tray 12) 17.0 33 90.9 h.l2 Three-four Seaside year old (Tray 5) U6.5 k7 93.7 U.21 oysters Chesapeake Bay (Tray 7) 31:^ 66 90.0 4.27 (Tray 8) 27,0 57 95-5 3.98 ■162- Literature Cited Hewatt, W. G. and J. D. Andrews. 195^- Oyster mortality studies in Virginia. I. Mortalities of oysters in trays at Gloucester Pointy York River. Texas Jr. Sci. 6 (2): 121-133. Mackin, J. G. 1951- Incidence of infection of oysters by Dermo - cystidlum in the Barataria Bay area of Louisiana. Conv. Add. Nat. Shellfisheries Assoc. 1951- Mackin, J. G., H. M. Owen, and A. Collier. 1950. Preliminary note on the occurrence of a new protistan parasite, Dermocystidium marinum n . sp. in Crassostrea virginica (Gmelinyi Science 111: 320-329. Ray, S. M. 1952. A culture technique for the diagnosis of infections with Dermocystidium marinum Mackin, Owen, and Collier, in oysters. Science Il6:360. .163- STimiES OF PATH0GEI3ESIS OF DERMOCIBTIDIUM MARDJUM &. M. Ray Sice Institute, Houston, Texas J. Go Mackin Marine Laboratory, Agricultural and Mechanical College of Texas, Galveston A considerable series of studies have been carried out by the authors, some as collaborations and some independently, which have aimed at measuring, as accurately as possible, the effect of in- fections of Dermocystidium marinum , a fungous paxasite, on their host oyster, Crassostrea virginlca . This paper aims to summarize the re- sults of these studies. The detailed descriptions of the various ex- periments will be published elsewhere. Methods In all cases oysters used in experimentation were disease free prior to experimental infection, as shown by check of representative samples by the thioglycollate method (Ray, 1952) « All oysters dying in the course of the studies were checked and graded for intensity of infection by the same method, as were also all survivors. The in- tensities were graded according to the definitions as presented by Ray, (1953). Infections were induced in the experimental oysters by exposing them to fungous cells obtained by maJting minces of the meats of dis- eased oysters using a Waring Blendor for that purpose. Two techni- ques were used in exposing the oys"oers to infection. In the first of these, the tissue minces of the diseased oysters were mixed with the water of the experimental aquaria. This method is referred to as the "feeding" method because it is assumed that in most cases the in- fective cells are ingested by the e:cperimental oysters and entry into the oyster tissue is via the gut epitheliim route. In the other method, the tissue mince is Injected into the shell cavity of the oyster through a small hole, bored through the shell. Oysters so "injected" are held out of wa.ter for a period of 15 to 2k hours •until penetration of the infective fungous cells has been accomplished, and it is ass\jmed that the cells penetrate the mantle, gill and general body epitheli^mi. In some of the experjjnents, aerated sea water in closed aquaria was used, the water being changed at about weekly in- tervals. In the remainder of the studies, a system of filtering run- ning sea water was \xsed, the filters of glass wool preventing in- fection of the controls . In all cases control oysters were treated as were the experi- mental oysters, with the exception that the minces of oyster meats to -l6h- which they were subjected were made up of oysters which were free of D. marinum infection. Some of the oysters used in making up the control minces were gapers and their tissues had been invaded by saprophytic bacteria. Data The data derived from these studies are incorporated in Table I. Discussion The data presented in Table 1 hardly need discussion. They show that D. marinum can destroy oysters, and under the conditions of the experiment destruction of all infected oysters will result if the experiments are continued over a long enough period. High water tem- perature is one of the conditions of experiment since all were carried out in summer or late spring. Data have been presented in previous years (Mackin, 195l) to show that under field conditions nearly 90 per cent of gapers re- covered were in stages of acuie fungous disease. Unpublished data have shown that uninfected oysters placed in endemic areas of dis- ease become infected about as rapidly as do those in aquaria and develop high mortality of approximately the same order as do those experimental oysters held under aquariicm conditions. The data pre- sented in 1951 have been vastly supplemented since that time and there caji be no doubt that heavy intensities of infection are the rule on planted beds throughout the heavy mortality areas of the oyster producing bottoms of Louisiana. The experimental data pre- sented here corroborate the Inferences derived from the field data that D. maj?inum infection of oysters is highly lethal when the dis- ease develops to acute stages, which it does in a very high percen- tage of cases both under field and laboratory conditions. -165- CO CO IP ^ CO O 00 O CO •a u cd T3 Ft O • a§ jd CO 0) Cd cc; cq ;a a) to H-q O (U 0) ■P * H r-i O n C\J cnvO m en cnvo ?J«* to ^^ Ch mo 00 H sO en ON en a H 0) CO bO o Cd 'ti U 00 0) CO Literature Cited Mackin, J. G. 19510 Incidence of infection of oysters by Dermo- cystidium in the Barataria Bay area, of Louisiana, Nat. Shellfisheries Assoc, Conv, Add, 195IS £2-3^ „ Ray, So Mo 1952, A technique for the diagnosis of infection with Dermocystidium marinum in oysters, Wat, Shellfisheries Assoc. Conv. Add, 1952s 9-I3, Ray, S, M, 1953 • St'udies on the occurrence of Dermocystidium marinum in yovtng oysters, Nat, Snellfisheries Assoc, Conv. Add. 1953: '80-88. .167- STUDIES ON THE Sr'KCCT OF IPPECTION 3Y DERMCCiSTlDrai4 MAHIMJ/I ON CILIARY ACTION IN OYSTE-RS (CRi\SSOSTREA VIRGINICA) J. G» Mackin Marine Laboratory^ Agriciilt-jral and Mechanical College of Texas, Galveston S. M. Ray Kice Institute, Kou&ton, Texas Introduction Analyses of the effect on oysters of infection with Dermocystid - ium marinum have been made over a period of several years . It has been shown (1) that there is a definite association of the disease with dead and dying oysters in the field (Andrews and Hewatt, 1953; Mackin, 1953), (2) that extrerae damage is done to tissues in the coarse of the disease (Mackin, 195^^ (3) that heavy losses in weight of tissue are incurred resulting from infection (Ray, Mackin, and Eoswell, 1953), (^) that the disease is water borne, and that transmission may be direct (Mackin 1951b; Ray, 195^), snd (5) that infections are highJ.y lethal (Ray and Mackin, 195^^ Mackin, Ray, and Boswell, 195^) • Continuing the analysis of effect of D. marinum on oj^ters, several studies of a physiological type designed to measure the effect of infection on ciliary accion were set up. The data resulting from these studies are presented here. Methods Eo L. LivnH invented a very efficient method of measuring ciliary activity and feeding in oysters » The basis of his method is measure- ment of the amounts of faecal and pseudofaecal matter deposited by oysters. This is the material extracted from the surrounding water by ciliary action, and when faecal matter is measured it becomes a measure- ment of feeding activity. These activities are physiologically basic and irreversible depression or cessation of ciliary activity may be taken as an indication of extreme weakness » The apparatiis designed and made by Lmid to catch faecal and pseudofaecal matter consists of a long lucite aquarium (Fig. l) whicTi is divided into three independent longitudinal tro-'oghs . Each trough is further subdivided into six compartments. Depending on the size of the oyster each compar-tment may be subdivided by baffles into 3 or 6 in- dividual supports in such manner that the hinge of the shell is down, and faecal matter collects on one side, pseudof£.ecal matter on the other. Median dividers separate the tvro sides of an individual cell» Figure 2 shows oysters in position in one compar'cment of the Lund aq\iarium. .168- ^^l^^ilfiiMi Fig. 1. A view of the experimental apparatus used for Experiments Number 1, 2, and 3- Above is a constant head tank provided with an overflow which regiilated the pressiire on the water flow. Three tubes lead from the bottom of the constant head tank to the three longitudinal troughs of the lucite tank. The level of water in the troughs was regulated by means of overflow tubes which are not visible in the photograph. Measurement of the amounts of faecal and pseudofaecal matter was done with the graduates in the fore- ground. A settling period of 2^ hours in the graduates was allowed before readings were made. 169 ^ Fig. 2. The positions of the oysters in the troughs are shown here. They rest^ hinge down, on the rounded lucite supports and are separated from each other by the slanted partitions. Faecal matter collects on the dorsal side of the median partition; and pseudofaecal matter, on the ventral side. The ventral sides of the oysters are toward the observer in this photograph. 170 An equal flow of sea water was maintained through each of the three troughs, the water entering at one end and leaving the other. A constant head tank was used to maintain constant pressure and the tapered tips of the inlet tubes were matched for size to regulate the amount of water flow. The turbidity of the water varied during the period of the experiments but control and experimental troughs varied together » The inlet tubes were cleaned once or twice daily and checks were kept on the volume of the water flow to see that it did not vary materially between control and experimental oysters, or from time to time. The deposited pseudofaecal and faecal matter was pipetted at intervals into 100 milliliter graduates, allowed to settle for a period of exactly 2^ ho-ors, and the amounts recorded. In some cases records for individual oysters were kept, in others the records were kept by compartments . Experimental oysters were matched for size with control oysters. In Experiment 1, each experimental oyster was matched with a corres- ponding control oyster by shell length. In Experiments 2 and 3 "the oysters were matched by weights. In Experiment 2 the control oysters totaled slightly less than the weight of the experimental oysters which was unavoidable considering the methods of selecting the con- trols . Further methods peculiar to each study will be discussed in the individual sections. Experiment Niomber 1 Experimental oysters used in this study were taken from a planted bed in Louisiana owned by Mr. Emmet Eymard. He had reported a considerable mortality, and a study of his oysters showed that about 67 per cent were infected with D» marinum and the intensity was relatively high. The oysters were checked for intensity by the thioglycollate method (Ray, 19'32). Control oysters were taken from the Chene Flexor station and were matched for size with the experi- mental oysters. A check of a sample of the controls for disease showed that they were free of disease at the beginning of the study but certainly picked up some infection during the study. All control and experimental oj'sters were csxefully cleaned of silt before placing them in the Lund aquari^jm. There were I8 oysters in each group. A flow of 1000 cCo per minute of sea water was introduced into the upper end of both the experimental and control troughs and the oysters were placed in position and the study begun on April 26, 1952. On May 5? 1952, the study was brought to a close and the faecal and pseudofaecal matter produced by control and experimental oysters was measured for volume, and the amounts recorded for each compartment of three oysters separately. ■171- Pes'olts The data from Exper'lment Kumber 1 ar-e contained in Table I» Table I Amoimts of Faecal and Pseudofaecal Matter in cC= P3TOduced by Control (Uninfected) and Experimental (Mostly Infected) Oysters in Experiment ^o, 1 Compartment 1 2 3 k 5 6 Total Control Oysters io6 178 198 20'^: 214 107 1008 Experimental Oysters 166 130 n? 23 15k 29 6lh A peculiar pattern was established by the control oysters, so far as a comparison of the amounts produced in the various compart- ments is concerned. 'Water entered the number one compartment and thus the amount of suspended silt must have teen highest in this one. It decreased aucessively through the trough from there to the end compartment, number 6, However, the efficiency of the oysters in removing the materials apparently increased with the decrease of the amount of s'ospended silt, for the amount precipitated by ciliary action Increased through the first five compartments. Appar'ently the small amount of silt remaining became a limiting factor when the sixth compartment was reached, for only half as much 'was precipitated as wa5 the case in compartment 5- The pattern of precipitation of silt for the e:x3)erimental oysters was rather irregular. Oysters of compartment number 1 pro- duced the greatest amount, those of compartment number 5 "the next largest, and those of number four the least. No experimental compartment attained the average amount pro- duced by the controls . In the case of the experimental oysters, the erratic variations in amount of faecal and pseudofaecal material produced in the different compartments probably represented variations in disease intensity. According to the sample checked for incidence of the population, one third was not infected, and another third was lightly infected. Thus 'I72- it is possible that loninfected oysters were placed in compartments 1 and 5 (which compare favora'bly with the controls), while in com- partments h and 6 (in which deposits were negligible in amount) there were two or three oysters in advanced stages of disease. The total amomat of combined pseudofaecal and faecal material produced by the diseased oysters in the experimental aquarium was only 6l per cent of the amount produced by the control oysters, show- ing a considerable ciliary depression caused by the infection. Experiment Kumber 2 Oysters used in this study were raised from spat at the Chene Fleur field station in Louisiana. At the time of this study they were just over two years old. Each oyster was weighed and they were then matched in pairs for equal weight. In all, 22 pairs were thus matched for weight. One of each pair was artificially infected with D. marinum using the injection method (Mackin, Ray, and Boswell, 195^) Since this involved injection of infected tissue mince into the shell cavity, the other oyster of each pair was similarly injected with a mince of uninfected oyster tissue. Since the oysters used were not free of disease to start with, it was hoped by this method to obtain a considerable number of heavily infected oysters to compare with a group of similar size which were uninfected or with light infections. When placed in the L^ond tank, they were so arranged that the artifi- cially infected group which could be depended upon to develop heavy infections was placed in one trough and that group from which it was expected to get controls was placed in another p9.rallel trough. Only l8 pairs of oysters were used in initiating the study, since it was assumed that there woiild be mortalities. The four extra pairs were used to replace the early mortalities. When an oyster died it was removed along with the one matched to it by weight, and another matched pair was used for replacement. The volume of pseudofaecal and faecal matter produced by each oyster was recorded along with the number of days of production. At the end of the study, or at the time of death each oyster was classed for intensity of infection by the thioglycollate culttire method. In this manner data on ciliary action and feeding of a number of oysters in various stages of disease, as well as some ujiinfected controls, were obtained. These data were reduced to pseudofaecal and faecal productlon per oyster per day. Results The data are presented in Table 11. Those oysters dying or removed in one day were eliminated because the data were not considered •173- TaMe II Basic Data from Experiment No. 2 Fseudo- Oys- Infec- Faecal faecal Pseudo- Oys- ter tion produc- produc- Faeces faeces xer vt. inten- tion in tion in per per Total No, gmso Days sity cc cc. Total day day per day Averagi 1 72.5 2 H 3.0 4.0 7.0 1.50 2,00 3.50 2 68.5 8 H 2.0 4.5 6.5 0.25 0.56 0.81 3 66.0 5 H 2.0 2.5 4.5 0.40 0.50 0.90 k 59-3 6 H 2.0 4.0 6.0 0.33 0,67 1.00 5 74.7 13 H 5.0 6.0 11.0 0.38 0.46 0.85 1,48 6 75.5 7 H 8.0 12.0 20.0 1,14 1,72 2.86 7 76.5 15 H 6.0 9.5 15.5 0.40 0,63 1,03 8 75.9 14 H 6.0 7.0 13 = 0.43 0.50 0,93 9 7O0O 15 M 11.0 15.0 26.0 0,73 1.00 1.73 10 68.5 15 M 8.0 11«5 19.5 0.53 0.77 1.30 11 78.6 15 M 9.0 10.5 19.5 0.60 0.70 1.30 12 77.5 15 M 8.0 llo5 19.5 0,53 0.77 1,30 1 = 39 13 75o5 15 M 9.5 7.5 17.0 0.63 0,50 1.13 14 75.0 15 M 10.5 13.0 23 = 5 0,70 0,87 1.56 15 73.5 13 L 19^5 34.0 53.5 1.50 2.62 4,11 16 74.5 15 L 12.5 19.5 32.0 0.83 1.30 2,13 IT 76.5 15 L 9.5 9.5 19»0 0.63 0.63 1,27 18 71.4 6 L 4.0 4,0 8.0 0,67 0.67 1.33 2.07 19 67.8 8 L 3 = 5 . 6.0 9.5 0,44 0,75 1,19 20 68.0 15 L 16.5 19.0 35 = 5 1,10 1,27 2.36 21 75o5 7 VL 12.5 3O0O 42,5 1.79 4,30 6.10 22 71.5 6 VL lOoO 20.0 30.0 1.67 3.33 5.00 23 74.5 15 VL 14.0 17.5 31.5 0,93 1.17 2.10 3.58 24 77.5 15 VL 7«0 10,0 17.0 0.47 0,67 1,13 25 73.5 15 N l4cO 33 = 47,0 0.93 2.20 3.13 26 72.0 2 N 5=0 5.0 10.0 2,50 2.50 5.00 27 70.0 15 W 15.0 20.0 35-0 1.00 l»33 2,33 3,40 28 65.5 5 N 11.0 17.0 28,0 2.20 3,4o 5.60 29 78,8 15 N 12.5 15.5 28,0 0.83 1,03 1.86 30 59^7 6 N 7.0 8.0 15.0 1,17 1.33 2,50 -174- significant. This left a total of 30 oysters, of which 8 were heavily infected, 6 were moderately infected, 6 were lightly infected, h very lightly infected, and 6 were negative for disease. The data on pseudo- faecal and faecal production for individual oysters and for each in- fection cIelss are contained in the tatle. The production for differ- ent classes of acutely infected oysters (moderate and heavy infections) are not significantly different. Those lightly infected are inter- mediate in capacity, and those very lightly infected and those negative do not differ significantly from each other. But when those acutely diseased are compared with those negative for D. marinum and very lightly diseased, the contrast is very striking, for those in stages of advanced disease produced only about kl per cent as much pseudo- faecal and faecal matter as did those not diseased. The data are further broken down in the graph Figure 3 • Experiment N^umber 3 Experiment JTumber 3 was set up on August l^i, 1953) and the study was terminated at the end of a 21 day period. The oysters used in Experiment Number 3 were obtained from Milford, Connecticut, through the coiortesy of Dr. Victor Loosanoff, Director of the Milford Labora- tory of the U. S. Fish and Wildlife Service, and Mr. Joseph Uzmann, of the same Laboratory. A considerable sample of these oysters was checked by the thioglycollate method to determine whether there were any infected ones among them. No infected oysters were found. Experi- mental oysters were infected with Dermocystidium by the injection method, the injections taking place on August 13, 1953" All oysters were weighed and matched in triplets; one of each three was a control and the other two were used in experimental groups A and B. Each of the two experimental groups contained nine oysters and the control group contained nine oysters. The data show that the injection method was successiu-1 in producing immediate infection in all experimental oysters. Control oysters picked up a considerable natural infection from the water flow, but no control oyster reached a heavy infection stage in the period of the study and none died. On the other hand 67 per cent of the experimental oysters (both groups) died prior to the end of the study (21 days), and on the following day two more died, making a total of 78 pe^ cent. Excepting as noted, Experiment Number 3 followed the procedures for Experiment Number 2, receiving the seme water flow. All three divisions of the Lund trough were used, the controls in the right side. Experiment A in the middle, and Experiment B on the l<^ft. In assessing the study the following points should be kept in mind. (l) All oysters started out equal as regai'ds infection. (2) Experimental oysters received a massive initial infection by injection of infective elements into the mantle cavity, and were all infected on '175- EXPERIMENT 45 N VL L M H INTENSITY OF INFECTION Fig. 3- Experiment No. 2. Graphic illustration of the production of faecal and pseudofaecal matter by infection classes of the oysters used in this study. The intensity of infection in each class is indi- cated at the bottom of the column. The left hand scale indicates the amount of material precipitated in cubic centimeters. 176 Table III Basic Data from Experiment Fo. 3 Period: August ik to September ^, 1953 Faecal Pseudo- Averages of expei imental Intensity Faecal Fseudofaecal matter faecal Total and con- Oyster of matter matter per per per trol oy£ No . Days infection in cc. in cc. Total day day day ters Experiment A 1 21 H 22.0 i^5o5 67^5 lolO 2.16 3.20 2 ' 21 E 17-5 26.0 k3-5 0.83 1.2i+ 2.07 3 21 H 11.0 2U.0 35-0 0.52 l.lU 1,66 k 19 H 13.5 26.0 39 = 5 0.71 l»37 2.08 5 5 M 3oO 7.0 10.0 0.60 1.1+0 2.00 1.86 6 21 H 10.0 31.0 Ul.O 0.U8 1.1+7 1.95 7 15 H 7-0 11.0 18.0 0.k6 0.73 1.20 8 6 H 2.5 5.0 7.5 0.U2 0.83 1.25 9 l6 H B.5 12.5 21.0 0.53 0.78 1.31 Experiment B 10 17 H l9o5 3k.3 5^-0 1,15 2.02 3.17 n 21 H 18.0 • 37«0 55.0 0.86 1.76 2.60 1? 18 H 13.0 2i|.0 37.0 0.72 1«33 2,05 13 15 H 9.5 16.5 26.0 0.64 lolO lo73 Ik 15 H 9.0 16.5 25 ^^5 0.60 1.10 1.70 1.90 15 17 H 8„0 19.0 27.0 Ooi^7 1.12 1.59 16 16 H 8.5 19^5 28.0 0.53 1,22 1.75 17 12 H 5.5 12,0 17.5 0.U6 1.00 1.1+6 18 21 H 7.0 16.0 23.0 0.33 0,76 1.09 Control - Group 19 21 MH 29.0 69.0 98.0 1.38 3=27 1+.66 20 21 M 23.5 83.0 106.5 1.12 3«95 5.06 21 21 E 17.5 51.5 69.0 0.83 2.1+1+ 3,28 22 21 M 1U.5 28.5 43,0 0.69 1.36 2.01+ 23 21 MH 13.0 25.0 38.0 0.62 1.19 1,81 2.68 2k 21 MH 15.0 3^.5 U9.5 0.72 1,64 2.35 25 21 MH 11.0 22.5 33»5 0.52 1.07 l»59 26 21 L 15.0 20o5 35^5 0.72 0.98 1.69 27 21 LM 13.0 21.5 3^.5 0.62 1.02 l,6U •177- the first day. This irrfectlon was added tc by natural infection from the water stream, (3) The infection proceeded rapidly in the ex- perimental oysters, ranging probably from light to moderate in the first week, from m.oderate to moderately heavy or heavy in the second week, and attained a heavy level in all oysters by the end of the third week. Becaiise of this progressive development of intensity from zero to heavy, faecal and pseudofaecal production should show an inverse level of production, becoming less from week to week. (4) Control oysters also, with one exception, became infected from the natural water stream. (5) Level of infection in the control group was never as high as in the experimental group, but more than half had attained a level of acute disease (but not heavy) by the end of the third week. (6) Progressive development of disease in the control oysters should be reflected in decreased faecal and pseudofaecal matter, at least by the end of the third week. (7) The decrease should not be great in comparison to that shown by the experimental oysters, because of the difference in level of intensity of disease. Results Table III contains the basic data derived from Experiment Number 3> in terms of totaZ production of faecal and pseudofaecal matter. Exper mental groups A and B were nearly equal in production of pseudofaecaJ. and faecal ma.tter, and these two were much below the level of the controls. Assuming that the level of the controls re- presents 100 per cent, the two experimental groups produced only approximately 7I pe^ cent. These data are presented graphically in Figure h. The data showing weekly production of faecal and pseudofaecal matter are also presented in Figure k. In computing the values on a weekly basis, al]. oysters producing for a part or all of each week were included in the c ale \ilat ions. In the case of those producing for only a part of the week, the production figures were increased proportionately to represent a fuJLl week. As shoTrrn by the graph, ciliary and feeding action was not only considerably less in the experimental oysters, but it decreased progressively for the three weeks of the study aa infection intensity increased. The controls showed a different pattern. Ciliary activity and feeding showed a distinct increase in the second week over the first. This probably was due to acclimatization to the aquarium conditions. The third week showed a drastic slowing down of cilia^-y action as the acute disease stage was reached in some control oysters. -178- EXPERIMENT 53 TOTAL FflECfiL flNO PSEUOOFftECAC EAECAL MATTER PRODUCED PER OYSTER PSEUDOFflECiL MaTTER PRODUCED PER MATTER PRODUCED PER OYSTER PER WEEK FOB THE THREE WEEKS OF DfSTER PER WEEK FOR THE THREE WEEKS PER DAT EXP 53 EXPERIMENTS A 8 S COMBINED OF EXP 53- EXPERIMENTS A 6 B COMBINED 3 6 EXPERIMENT - ^H IB CONTROL - 1 1 q: 5 ^ _ 15 CL i K Q i 1 ^ 2 ^ " - - 12 o o 1 1 < ir a fe fe S 5 - - 9 1 - 2 1 - 1 1 - 6 3 CONTROL EXPER A EXPER B 2 3 Fig. k. Experiment No. 3- Graphic representation of the effect of Dermocystidium mariniim on ciliary action and feeding of oysters. On the left is shown a comparison of the total production of pseudofaecal and faecal material in controls and experimental oysters. In the center is a comparison of faecal production per oyster per week for the three weeks of the experimentation. On the right is a similar graph for pseudofaecal production. The latter two not only compare the controls with the experimental oysters, hut show the decrease in ciliary action as disease intensity rises. 179 Discussion The three studies described here show that physiological ah- normality accompanies the development of Dermocystidium disease in oysters. Retardation of ciliary activity of the gills not only affects feeding^ hut also produces derangement of respiratory function. It is interesting that even light infections by Dermo- cystidium produce a meaisiireahle decrease in ciliary action, and it may well he that this depression sets up the vicious cycle of weakening which in turn results in miliary spread of disease, pro- ducing even more severe respiratory derangement. In this connection it may be noted that it is not thought that decreased feeding materially speeds death of an oyster from Dermo - cystidium disease. The disease works far too rapidly for that to occur under summer conditions. Cessation of feeding by acutely diseased oysters is to be considered as a symptom, and as evidence of physiological abnormality due to disease, but our studies have shown that, all other things being normal, it takes a very long time to starve an oyster to death. -180- Literature Cited Andrews, J. D., and W. G. Hewatt. 1953- Incidence of Dermocystidiijii marinum Mackin, Owen, and Collier, a fung\is disease of oysters in Virginia. Wat. Shellfisheries Assoc. Conv. Add. 1953: 79 (abstract) . Mackin, J. G. 1951a. Incidence of Infection of oysters by Dermo - cystidium in the Barataria Bay area of Louisiana. Nat. Shellfisheries Assoc. Conv. Add. 1951 •22-35- Mackin, J. G. 195Ib=. His topatho logy of infection of Crassostrea virginica (Gmelin) by Dermocystidium marinum Mackin, Owen, and Collier. Bull. Mar, Sci. Gulf & Carib. l(l): 72-87. Mackin, J. G., S. M. Ray, and J. L. Boswell. 195^» Studies on the transmission and pathogenicity of Dennocystidium marinum II. In press. Ray, S. M. 1952. A cxilture technique for the diagnosis of in- fections with Dermocystidium marinum Mackin, Owen, and Collier, in oysters. SciencellS~T30l"5jr3^-36l. Ray, S. M. 195^'' Experimental studies on the transmission and pathogenicity of Dermocystidium marinum , a fung^ix parasite of oysters. Jr. Paras it. 40(2): 235. Ray, S. M. , and J. G. Mackin, 195^- Studies on the transmission and pathogenicity of Dermocystidium marinum I. In press. Ray, S. M. , J. G. Mackin, and J. L. Boswell. 1953- Quantitative measiorement of the effect on oysters of disease caused by Dermocystidium marinum . Bull. Mar. Sci, Gulf & Carib. 3(l): ^^33"^ -181. A HAPLOSPORIDIM HYPERPARASITE OF 0Y3TEES Jo Go Mackin Marine Laboratory, Texas Agricultviral and Mechanical College, Galveston Harold Loesch Department of Conservation, Bayou La Batre, Alabama Introduction Oystermen operating in Mobile Bay, on Kings' Bayou and Buoy Reefs and the south pai't vOf Whitehouse Reef, complained of excessive mortali- ties of oysters ( Crassostrea virginica ) in the late sijnmier and fall of 1953- They described oysters as heing blackish in color on the vis- cera and mantle, but did not definitely connect this characteristic with the mortality. It appears that their examination was of live survivors and they probably did nox examine gapers . In an effort to determine what was the cause of the reported mortality, several samples of oysters were sent to the Grand Isle Laboratory of the Texas A.& M. Research Foundation for study. A check showed that the samples had a comparatively high intensity of infection with Dermocystidium marin'om which accounted for the reported mortality. However, there was no correlation with the blackening which had been described. A thorough search revealed only one oyster with such characteristic. The sides of the viscera of this one were streak- ed with brownish black ai'eas which extended down into the mantle and palps. This oyster had only a light infection with Dermocystidium , and a few Nematopsis spores were found. Sections through the visceral region of this oyster were made and the slides were vario\.isly stained with Giemsa, Heidenhain's iron haematoxylin, and Delai'ield's haematoxylin and eosin. These slides showed that the oyster was heavily infected with Bucephalus , and the sporocysts and cercariae were in turn parasitized with a Haplosporidian gporozoan. The sporocj/^sts had been destroyed by the sporozoan. and only remnants of host tissue and the cuticular walls remained, some areas the Bucephalus cuticula had broken d.o\ra liberating the spores into the oyster host tissue. Intense cellular reaction was evident in these areas, and a careful search showed t]rat the hyperpara- sites had been carried through vasc"alar channels and the remnants of the gonadal ducts of the oyster host and were generally distributed through the tissue. They were undergoing development, but the develop- ment was obviously abnormal. Spores and amoebula stages could be seen in leucocytes, and in some epithelia of the oyster host. Generally speaking, however, the oyster tissues seemed normal, excepting for the local cellular reactions already referred to- -182- Development of the Haplosporidian All stages of development were easily observed in the Bucephalus sporocysts. Free amoeloulae were seen scattered in the cavity of the sporocysts or occasionally in the epithelia of the host worm where such tissues were not destroyed. Most of the stages of development were found free but may originally have been intracellular. Since most tissues of the sporocyst host were destroyed prior to section- ing, the developmental stages appeared to be free in a cavity bounded only by the cutj.cula of the worm. A direct development takes place resulting in mioltinucleate Plasmodia with variable numbers of nuclei up to more than fifty. Mature spores may form in the sporocysts in any stage from about 12 nuclei up. In the leucocytes of the host amoebulae may form capsules without going through divisions of the nucleus, which res\ilts in fonnatlon of single spores. These latter are cytologically as they are when they escape from the spore capsiile which escape is accomplished by rupture of the spore case. There is no "lid" to the spore. Vacuoles form in the cytoplasm as the amoe- bulae grow and with successive steps in development of the plasmodial syncytium. When the definitive number of nuclei is attained, islets of cytoplasm form around the nuclei, followed by deposition of the spore wall. The spores themselves are variously shB,ped according to the pressure of surrounding tissues, but are usually ovate, about 3 to 5 by 5 to 7 vi. The apparent absence of a polar filament places this sporozoan in the order Haplosporldia Caullery and Mesnil. Certain phases of the development are so obviously parallel to those of the Micro- sporidia that it is thought best to indicate that this placement in no way indicates a relationship with the aberrant Icthyosporidium or Bertramia which have been referred to the haplosporidian wastebasket. The parasite of sporocysts of Trematodes in Donajc trunculu s (Europe) is a parallel case of hypsrparasitism (Ca\illery and Chappellier, 1906) , and there are several other' similar hyperparasites among the Micro- sporidla and the Haplosporidia, The hyperparasite of Trematodes in Donax trunculus ( Anur-osporidiimi pelseneeri ) is not the same as the form described here, since tne spore in that species is described as spherical and has a small operculum. Investigation has shown that Donax variabilis from the Texas coast has a Haplosporidiaii parasite of Trematode sporocysts, but preliminary study indicates that this one is neither Anurosporidium pelsen eeri nor the hyperpar as ite reported in this paper. However, it is thoi.ight best to resex-ve final judgement in this matter, pending study of more material. Literature Cited Caullery, M,, a.nd A. Chappellier. I906. Axiurosporidium pelseneeri n, g,, n. sp,, Haplosporidie infectant les sporocystes d'un Trematode parasite de Donax trunculus. C. R. Soc. Biol. Paris 60 : 325-328. -183- EFFECTS OF TOO PARASITES ON THE GROWTH OF OYSTERS R. Winston Menzel and Sewell H. Hopkins Department of Biology, A. & M. College of Texas College Station This report is based on an experiment conducted by my colleague, Dr. Menzel, at Bay Sainte Elaine oil field in Terrebonne Parish, Louisiana. On May 1, I9U8, Sea Rac trays containing a mmiber of i+ by 3 inch strips of roofing tin were placed in the bay. The tin strips were held in place, in a vertical position. On June 26 all but one of the numerous spat were cleaned off of each side of each strip, and each was marked by a number on the metal. The height and length of each spat was measured each month. Between J'one 26 and October 28 some of the original spat fell off and were lost, and these were re- placed by younger spat which had set on the tin strips. October 28 was the end of the setting season, so no replacements were made after that date. On December 20, 19^8^ all of the youiig oysters were re- moved from the plates, and each was marked by a number painted on its shell. On January 23, 19^9? and once each month thereafter, each oyster was weighed Individually, three dimensions (length, height, and thickness) were measuj"ed, and the total vol\jme of all oysters in each tray was determined. A record was made of the average length, volume, and weight of all of the oysters in one tray from May 19^8 to the end of the experiment in May 1950. These average measurements are very nice for making pretty graphs, but averages do not tell everything. We were more interested in the differences between the individuals and the reasons for those differences. Incidentally, the fact that a few oysters which had been added to replace lost spat were one, two, or three months younger than the original ones did not make any difference in the long run. Within a year these younger oysters were as large as the oldest ones, or even larger. Now, we had noticed in other experiments, as well as this one, that oysters which grew very slowly us\;ially ended by dying while the faster growers siirvived. Looking back over the records of an oyster which died, we usually found that it had stopped growing or had even lost in length and weight for several weeks or months before it died. The ones that died had grown very little or none at all during the last fovir or five months, while the survivors had continued to grow, on the average, at an midimlnished rate. Only one tray was kept to May 1950. The 23 sur^rivors in this tray were fixed and sectioned. Dr. Mackin, who had never seen the ■iBll- individual growth records, was asked to examine each slide for Dermo - cystidium marinimi . On the basis of his notes, we divided the oysters into three groups: uninfected, (8 oysters), lightly infected (9 oysters), and heavily infected (3 oysters) o There was also one oyster which was negative for Deiiao c ys t id iiaii but had a well developed infection of the trematode Bucephalus cuculus . The parasite had completely des- troyed the gonad and replaced it "by a mass of sporocystSa The Bucephalus infected oyster had shown unusually rapid growth. The oysters with light Dsmiocystidiuiii infections had grown at the same rate as the uninfected ones ujitil the last four or five months, and then lagged slightly behind» The heavily infected group (3 oysters) had "been growing at a slower rate for several months. A comparison of the increase in length of the same four groups during the same l6-month period shows that the Bucephalus infected oyster had stopped gaining in length, and the ones with heavy Dermo- cystidiim infections had not gained for five months » We had observed many times before that when an oyster is affected by some adverse factor, the gain in length quickly comes to a stop and the oyster may even lose several millimeters of the bill because the mantle is drawn back farther inside the shell, but it may continue for some tjme to gain in thickness and consequently in weight. At the end of the experiment. May 9> 1950^ "the largest individual with heavy Dermocystidj-um infection weighed lUl grams and was 83 milli- meters long, while the smallest one in the uninfected group weighed 127 grams and was 77 millimeters long, so there was some overlapping in final sizes. However, the largest oyster in the group heavily in- fected with Dermo c ys t id ium had gained only 22 grams in weight a.nd 2 millimeters in length in the last five months, while the smallest and slowest growing oyster in the uninfected group had gained 38 grams and 7 millimeters . In growth rate there was no overlapping. The data have been aiialyzed statistically. The analysis shows that the differences between the uninfected, the lightly infected, and the heavily infected oysters are real, and that there is less than one chance in one hundred that these differences are due to acci- dent or coincidence. The single Buc sphalus infected oyster was not included in the statistical study. We have no information on parasitism in the oysters which died d^jring this experiment, but Dr. Mackin has examined those which died in many other experiments. In a growth exper:Lment conducted by Dr. W. G, Hewatt during the same period (in 19^9) all of the 25 oysters which died proved to have heavy infections of Dermo c ys t id ium ; nearly all of these individuals had stopped growing some weeks before death, while the uninfected survivors had continued to grow at a rapid rate. -18 cr. We conclude that an infection by Dermocystidi-um usually causes a slowing and eventually a complete stopping of growth, long "before the oyster finally dies. Oysters may stop growing several months before death. Inclusion of paraisitized oysters in a growth experiment may change the shape of the growth ciirve, so a study of parasitism shoiild be made a part of every growth study. We have growth data on only one Bucephalus infected oyster. So far as we know, this is the only one on which anyone has any growth data. However, it is interesting that our Bucephalus infected oyster showed exceptionally rapid growth until the last two months of the experiment, for there are theoretical reasons for believing that this parasite may stimulate growth. It is well known to parasitologists, since the work of Miriam Rothschild in the 'thirties, that snails castrated by larval trematodes have rapid growth and prolonged life, resulting in giantism. The same may be true of oysters. So long as the sporocysts are confined to the gonad, Bucephalus infected oysters have large fat meats, even in summer when other oysters are poor. We know from personal experience that these caponized oysters ajre ex- ceptionally good eating. However, the sporocysts later spread to other tissues and seem to cause considerable damage. It may have been the effect of such a late stage infection that finally halted the rapid growth of our pet. -186- THE FJKCTIOMAL MORPHOi-OGY OF THE ALIMENTARY CMAL OF ASTER 3AS FORBES! AM) THE PREDATION OF EWALVE'.MOLLUSKS (a Sunmary) i'^ederick A. Aldrich Academy of Natural Sciences ; Philadelphia, Pennsylvania Introduction The importance of ths' common sea star Asterisk f oi-hes i (Desor) of the middle Atlantic coast as a predator of commercially important "bivalves has long teen recognized. Very little work has been done on the functional morphology and digestive physiology of this animal. The present report summarizes work on the functional morphology of the alijnentary canal of the sea star conducted as a part of a more comprehensive study which will appear in print elsewhere. The author is Indebted to the encouragement and direction of Dr. M. R. Carriker, now of the University of Worth Carolina, and to Dr. Victor L. Loosanoff, through whose cooperation much of the work was performed at the Milford Laboratory of the U. S. Fish and Wild- life Service. General Aspects of the Alimentary Canal The alimentary canal of A. forbesl is s-aspended by mesenteries from the dorsal body wall In the oral-aboral axis of the central disk at the base of the antlmeres or rays. The mouth at the oral terminus is ringed by a peristomial membrane bordered by large per- ioreil spines bearing numerous pedicellariae. A short esophagus con- nects the mouth with the stomachal portion of the canal. The stomach is divided by a superficial constriction into two portions: an oral portion, the much convoluted and lobulated cardiac stomach, and an aboral pyriform portion, the pyloric stomach. From the mid intraradial siirfaces of the pyloric stomach five ducts arise, each of which soon bifurcates upon entering the antimeres, and then ramifies repeatedly into the multilobulated paired pyloric diverticula. The pyloric stomach leads aborad beyond the rad.ial diverticular ducts and abruptly tapers to the very short and slender intestine. The latter tenainates at the antis, when the anus is present. Two short botryoidal rectal caeca project interradially from the walls of the in- testine. -187- Everslon of Cardiac Stomach In the eoixTse of feeding on oysters and other' bivalves too large to be ingested the sea star everts the cardiac portion of its stomach through the mouth to cover the meat of the pelecypod prey. This phenomenon of extracorporeal digestion is characteristic of sea stars whose tube feet hear suckers (Schiemenz, I896) . It is the lohes of the cardiac stomach, or those portions which fill the pro- ximal ends of the antimeres, which are everted. Cuenot (1887) des- cribes the mechanism of eversion as one of pressures transmitted thi'ough the coelomic fluid following the contraction of the body walls. MacBride (1906) echoes this explanation of the mechanics of eversion. However, no experimental data has been offered to cor- roborate or deny this hypothesis. In the present study sea stars, up to 1^+ centimeters in dia- meter, were injected with known quantities of sea water after being relaxed with MgSO|^. The cardiac lobes were everted upon the injection of 10.5 to lU.O milliliters of water. The injection of 28 milliliters of sea water into an unrelaxed animal failed to produce eversion. Following extracorporeal feeding the cardiac stomach is with- drawn into the body of the sea star by muscular action. There are five pairs of cardiac retractor muscles, with origins on the ambula- cral ridge of each antlciere, at about ossicle 33-35^ or at a point one third of the length of the ridge. At the point of insertion of each of these muscles to the wall of the cardiac stomach the muscles bear hook-like calcareous structures, here named the "procardial restrictors. " The hooks are 2.8 millimeters in length on a retractor muscle measuring 3^°^ millimeters. The procardial restrictors of the paired cardiac muscles of each antimere are conn.eeted by a thin cal- careous bar, forming an H-shaped configuration, thus providing a common insertion for the paired muscles. When the cardiac stoma.ch is everted the procardial restrictors are locked on the circumoral ring of the endoskeleton, thus lilmiting the amount of tissue which is everted. It is difficult to visualize the withdrawal of the cardiac lobes by constriction of the retractor muscles alone. The ai-ea under the pro- cardial restrictors is pulled into the proximal portion of each anti- mere and may initiate the ret\a;rn of the stomach through the mouth. It is suggested that for the stomach to resume its normal position within the sea star the major component of the forces accomplishing this would be directed aborally. It is clear that the cardiac retractor muscles cannot supply these forces beca^ase of their sites of insertion. The mesenteries, previously mentioned, which suspend the stomach from the dorsal body wall are in a position to exert this force. It would appear that as the lobes are everted the mesenteries are greatly extended. Their site of attachment on the aboral walls of the stomach come to lie inside the ring of everted stomach tissue. Upon contraction the mesen- teries resume their nonaal position and in so doing draw the lobular por- tions of the stomach into the coelom. -188. Literature Cited Cuenot, L. I887. Contribution a I'etude anatomique des asterides. Arch. Zool. Exp. et gen. (2) 5: (supplement). MacBride, E, W. 1906. Echinodermata. Cambridge Natixral History. London. MacMillan ajid Company, Ltd. 1: 425-623- Schiemenz, P. 1896. Wie offen die Seestern Austern? Mittheilungen des Deutschen Seef ischereiverseins 11-13: 102-118. -189- SEASONAL vlHRTICAL MO\'EMEFrS OF 0"iBTER DRILLS ( UROS-ALPIMX CINEREA ) Melljoux'ne R, Carriker * Rutgers IJiiiverBity, New Brunswick, New Jersey Introduction A number of preliminary observations (Adams, 19^7; Cole, 19U2; Engle, 1935-361 Federighi, 1931; Galtsoff, Frytherch, and Engle, 1937; Gibbs, personal communication; Mistakidis, 1951; Orton, 1930; Stauber, I9U3) suggest that as water temperatures drop in the fall oyster drills, Urosalpinx cinerea (Say), at least in the northern areas of their geo- graphic range, exhibit certain migratory movements » Drills inhabiting subtidal surfaces crawl downward onto the bottom, and some of these bury in the sediment; some drills in intertidal areas also burrow in the bottom, and others migrate into deeper water. The reverse migra- tion is said to take place as water temperatures rise in the spring. Federighi (l93l) in North Carolina noted that drills retained in running sea water aqiiaria maintained at temperatiores prevailing outdoors became inactive below 50°F and remained attached to the substratum or lay passively on the bottom. A temporary rise in temperature above 50°F anytime during the winter stimulated slight creeping, and the activity increased as the temperature rose. Galtsoff, Prythereh, and Engle (1937)^ working in the laboratory in the northeastern states in water temperatures ranging from 26 to i+9°F noticed that locomotion in drills completely ceased below 35'>6°F; the drills either hibernated on the svirface or bixried in the bottom attached to partially bioried hard objects, with the tip of the siphon projecting slightly above the bottom. They discovered no evidence that drills seek and congregate exclusively in cavities of empty shells for protection during the cold weather. In Canada (l9^7) A_dams observed that hibernating drills attached to oysters and shells became covered with a layer of silt which hid their typical form, and made them very difficult to detect. Engle (1935-36) and Stauber (l9^3) both noticed in Delaware Bay that not all drills bury in the bottom since some were fo'und deeply wedged in crevices formed by clustex's of oysters. Stauber (19^3) reports that drills migrating off intertidal reefs in the fall were discovered later more or less completely biiried in the bottom ar'ound the edges of the reef usually clinging to shell and with siphons up and presumably in contact with the water. In the winter Engle (1935-36) noticed in Delaware Bay that the drill dredge collected drills on hard as well as on soft bottom, and that n-umerous drills were collected with a drill dredge equipped with a scraper bar, indicating that many of the snails were present on the surface or not far below it. ^Present address: Department of Zoology, University of North Carolina Chapel Hill, North Carolina .190. The precise depth to which drills hurrow, the proportion that paiss the wintei' thus buried, and details on the behavior of burrow- ing have not been recorded. Such information is of considerable interest to marine ecologists and to oyster farmers who may wish to eradicate drills from infested oyster bottoms during the winter. This report presents additional infonnation on the wintering over behavior of the oyster drill obtained in a series of laboratory and field studies carried out during the winter of 1953-5^ • Grateful acknowledgment is made to J. Richards Nelson and to the Ja & J. W. Elsworth Co. for support of the project. Laboratory Methods The laboratory studies were conducted in the Rutgers University Vivarium where it was possible to stimulate the prevailing outdoor temperatiires and to carefully observe the activities of drills during the period October 21 to March 17. A glass covered aquarium, with a bottom area of tr-zo square feet, located within the Vivariimi, was connected by one half inch diameter rubber and glass tubing to a glass covered hard rubber bucket placed outside of the Vivarium. The bucket was covered with aluminum foil to reduce warming from insolation. The bottom of the aquarium was filled to a depth of about three inches with three different types of sediment in equal parts: clean fine sand, coarse sand and gravel, and fine black mud. Sediments were overlaid with a layer about an inch thick of mussel shells, living mussels, and a few young oysters. Some of the shells were pressed deeply into the sediments. The 10 gallons of sea water (salinity range during the observations was 29°6 to 33-5 o/bo) in the system were continuously circulated at the rate of about a gallon every two minutes by means of an air lift pump. Sea water was changed every two months . Hydrogen ion concentration, determined weekly, fluctuated between 7°5 and 7»8 during the winter. Temperature of the water in the aquarium was recorded once or twice daily. Minimum water temperatures, 3^»8°T'; were encountered in December and with minor upward fluctuations lasted about three days. Unfortunately no subfreezing t;emperatures occurred. Two hundred oyster drills ranging in height from I7 to 3^ millimeters were distributed uniformly over the bottom of the aquarium and examined almost twice daily. Each day drills which had crawled onto the sides of the aquariimi during the previous day were returned to the bottom, and a count of these was employed as a partial index of the gross activity of the drills d\iring that period. A careful check was also maintained of the number and position of drills among the shells on the bottom, and of the number and behavior of drills which buried in the sediments along the sides of the aquarium. These were clearly visible through the glass on which the vertical position and outline of the foot was marked and dated with a wax pencil. At the end of the experiment before the drills became active in the spring their vertical stratification in the sediments was determined by successive sCKeening of one inch layers. -I9I" Laboratory Results In the fall at temperatur'es between 55 and 70 '1 as many as k2 drills cliniDed onto the sides of the aquarium per day^ During the first cold period when water temperatures dropped to Ul F movement onto the sides ceased altogether, 'but only after a lag of a'Dout 7 days during which water temperatures rose to a maximum of 6l°F, Thereafter temperat^jres in tne range of 52 to 70°5 "brought as many as 11 of the hardier drills onto the glass per day^ Fr'om the middle of December to the middle of March temperatures below ^1°F occixrred with sufficient frequency to almost, completely inhibit the movement of drills away from tne bottom. During the coldest part of the winter, Decenfcer 17-19j when water temperatures fluctuated between 3^.8 and 39°F, the disposition of the dr-ills did not change appre- ciably, except that drills seemed to move a little deeper among the shells and were less evident. During the winter about 50 drills remained visible among shells on the bottom. As the winter passed a fine layer of detritvis accom'olated snugly about them and made them difficult to detect, particularly those aggregated in the cavi- ties of upturned shells (Fig. l) . The remaining 150 drills stationed themselves under shell or in the sediment. Drills on the surface of the bottom displayed considerable activity and irritability even during low temperatures. At 3^°8°F some of the drills crawled slightly, with tentacles extended. These were slowly retracted when touched. Drills turned on their backs at this temperature had very slowly rigjrited themselves 8 hours later by which time the temperature had risen to 39°?- At temperatures between 3^ and 39°F most attached drills were easily dislodged. It was surprising to find that as early as the end of October at water' temperatures between 55 and 70°F a number of drills started crawling into the sediment along the glass of the aquarium. Since no snail was ever seen actually burrowing, the exact method of pene- tration is unkno-vm. But, because of the danger of blocking of the siphon with sediment and because no partially buried drill was ever seen with its siphon pointed into the bottom, it is possible that crawling into the bottom is performed backwards. In every observed case under these conditions buried drills remained partly or completely attached to har-d aurfaces and moved no deeper than the fleshy tip of the siphon which projected slightly above the surface of the bottom as a tiny yellow-brown bud. Thus xhe tip of the spire of the largest drills, which measured 3^ inni. in height, were buried about 1 l/k inch below the surface of the bottom^ Daring war-mer periods the yellow ventral surface of the foot of bijried drills approached the shape of a circle, and remained closely appressed to the site of attachment (Fig. 2). During periods below 4l°F the sides of the foot curled inward, leaving a furrow down the middle, and attachment was thereby considerably weakened (Fig. 3)» In a few cases palatial retraction of -192- Fig. 1. As the vinter advances a fine layer of detritus acciimulates snugly about drills, Urosalpinx cinerea (Say), remaining on the sur- face of the bottom and makes them difficult to detect, particularly those aggregated in the cavities of upturned bivalve shells. Magnifi- cation approximately natural size. 193 Fig. 2. The foot of a 'biiried drill, Urosalpinx cinerea (Say) , closely appressed to aquarium glass during temperatures above i|-l°F, and photographed through the glass from outside the aquarium. The siphon tip of the drill extends upward to the s\ir- face of the sediment hut is not visible in this photograph. Magnification approximately 2X. 194 Fig. 3. The foot of a buried drill, Urosalpinx cinerea (Say), loosely appressed to aquariiom glass during the lowest winter temperatures. At these temperatures the sides of the foot curl inward leaving a furrow down the middle, and attachment is thereby consider- ably weakened. Slight compaction of the sedi- ment (mud with some fine sand) is visible about the periphery of the foot. Magnification ap- proximately 5X. 195 the foot was observed » Flow of water fnrough the respiratory charn'Der of the drill, although probably much reduced, undoubtedly continues "diui-ing hiber- nationo Examination of buried drills suggests that water is drawn into the gill chamber through the siphon, which always appears to remain in contact with the water, and is ejected from the right side of the snail into the sediment to diffuse upward out of the bottom. This explanation is supported by examination of drills buried in soft mud. The mud immediately around and above the drills appeared oxidized and brown in color, clearly islanded from the sur- rounding reduced black mud. Although a few drills buried in the sand and gravel> the majority were foimd in the mud; in all cases burrow- ing seemed to occur over hard surfaces such as shell and glass. The depth to which different drills burled varied from a few millimeters to complete submergence a Drills also buried in deep depressions in the bottom, with siphon tips still in contact with the water, and thus were stationed some distance below the average level of the bottom^ Individually marked buried drills exhibited great variation in movement, although this movement was quite localized and in general did not exceed one half inch; it continued throughout the winter at temperatures approximately above 35»6°F» Many drills moved deeper, if partially buried, or horizontally, or upward, or sought -other hibernating sites, or did not buxy again j a few remained stationary for periods varying from a few to 56 days inspite of intervening warmer periods . Field Methods and Results The protected waters of Home Pond, Gardiners Island, New York, made possible the use of outdoor cages to determine the disposition of drills in the bottom during the winter. On October 1, foi^r cages approximately one cubic foot in size and open at one end, of one quarter inch galvanized wire, were pressed open side downward four to five in- ches into a variety of sand and mud bottoms in slowly moving tidal water. Each cage contained a layer about one to two inches thick of oysters and shell and 100 drills I6 to 26 millimeters in height, and was covered by approximately six inches of water' at low tide. Boat traffic and ice demolished three of the cages. The fourth cage, on firm fine sand, was dismantled during low water on November I8. About one half inch of mud had accumulated in the cage, Kinety-nine of the 100 drills, 91 alive, were recovered and all were buried in the mud cupped in empty shells or clinging to the underside of shells or to the sides of the cage, all within an inch of the siir- face of the mud. .196= An abundant population of lar-ge drills up to 3^ millimeters in height on the shoalei bottom of the Shark River Inlet, New Jersey, afforded a good opportunity to obser-ve the disposition of drills on native subtidal 'bottoms in swift tidal currents under natural winter conditions unobstructed by enclosui-es of any kind. Collections and observations were made on warm days at low water on December 6 and February 20= A small shovel with the handle bent at right angles to the blade was used to scoop up relatively undisturbed strata of the bottom. After macroscopic examination these samples were washed on one quar'ter inch mesh screen. Where dui'ing the previous summer drills were abundant on intei'tidal rockwork and on intertidal mussel covered bottom, no drills were found even at depths of six inches in the sediment. They did occur, and in quantities comparable to those collected Intertidally during the summer, on bottom below the low water line of a -O.k tide, especially at depths exceeding one foot. When present drills were not visible through clear water on the bottom becaiise of siltation. In layers of the bottom brought up carefully in the scoop they were found clinging to the under and upper surfaces of shell, and buried partly or to the siphon tip in sediment which had accumulated in upturned shells. This disposition was simi- lar to that observed in the aquarium studies. Summary and Conclusions These studies confirm the observations of earlier investigators and demonstrate that at least 75 P&r cent of the drills bury partly or completely in the bottom d\iring the colder months of the year in the New York-New Jersey area. Those that bury completely move no deeper than the siphon tip. Since drills also bury in depressions of varying depth, so long as they remain in contact with the water, they may occ\ir some distance below the average level of the bottom and thus escape the scrapers, teeth, and suction of drill dredges. Considerable variation in the degree of tor-por occurs among different dr-ills at temperatures above 35^^^. Complete inactivity probably does not occur except at temperatures below 35°F° Adherenqe of the drill to the substratum is noticeably weaker at lower temperatures, parti- cularly below i+l^F. This should faciliate drill dredging in the winter timej on the other hand the characteristic of many drills to crawl under partly buried shell in the level bottom and in depressions in- creases the difficiiLty of drill eradication during the winter. =197- Literature Cited Adams, J. R. 19^+7- The oyster drill in Canada. Fish. Res. Bd. Canada, Atlantic Coast Stas., Atlantic Biol. Sta., Note No. 99. Cole, H. A. 19^2. The American whelk tingle Urosalpinx cinerea (Say), on British oyster beds. Jr. Mar. Biol. Assoc. U. K. 25: 1+77-508, Engle, J. B. 1935-36. Preliminary report of the U. S. Bureau of Fisheries oyster drill control project in New Jersey, 1933-36. Unpublished manuscript, U. S. Bur. Fish., Washington, D. C. Federighi, H. 1931« Studies on the oyster drill ( Urosalpinx cinerea Say). Bull. U. S. Bur. Fish. k-J: 83-II5. Galtsoff, P. S., H. F. Prytherch, and J. B. Engle. 1937. Natioral history and methods of controlling the common oyster drills ( Urosalpinx cinerea Say and Euple\;ira caudata Say) . U. S. Bur. Fish. Cir. No. 25: 1-21+. Mistakidis, M. N. 1951' Quantitative studies of the bottom fauna of Essex oyster groiinds. Ministry of Agr. & Fish., Fishery Investigations Ser. II, 17(6): 1-1+7. Orton, J. H. 1930. On the oyster drill in the Essex estuaries. Essex Nat. 22(6): 298-306. Stauber, L. A. 19^3- Ecological studies on the oyster drill, Uro - salpinx cinerea , in Delaware Bay, with notes on the associated drill, Eupleura caudata, and with practical consideration of control methods. Unpublished manuscript, Oyster Res. Lab., N- J. Agr. Exp. Sta., Bivalve, W. J. -198- PRELIMINARY EXPERIMENTS IN THE USE OF GROUND CONTROLLED AERIAL PHOTOGRAPHY IN n>ITERTIDAL HYDROGRAPHIC SUR',/EYS Robert L. Dow Department of Sea and Shore Fisheries, Augiosta, i^Iaine Purpose The purpose of these experiments was to obtain base map data for hydrographic, hydrogeologieal, geological, biological, or com- bined geological -biological surveys of intertidal areas occujried by commercially exploited shellfish. In this paper the meaning of the term hydrography is limited to that branch of surveying which em- braces the determination of the contour of the bottom. Characteristically, hydrographie charts, topographic quad- rangles and even shoreline survey manuscripts developed from high altitude verticals lack the detailed accuracy essential to base map requirements for intertidal surveys. Discussion Earlier base maps had been obtained solely from ground sur- veys, a method which is both time consuming and expensive. Results in some areas are of questionable accuracy because of hydrogeological changes which could occur during the course of a several weeks survey. Casual observation between 19^6 and 19^9 of Western Beach, Scarboro, Maine, the area used in these experiments, had indicated that surface conformation and elevation were drastically modified from time to time. Two marked subareas were photographed at irregular intervals ijbetween July 19^9 and May 1950. These photographs demon- strated that changes in the conformation and direction of ripples took place during the period covered. Changes in ripple direction were assoCj.ated with changes in prevailing winds. During the summer the ripple -axis ran northwest southeast at nearly right angles to the prevailing winds from the southwest (Fig. l) . By mid winter the axis was nearly southwest-northeast (an estimated turn of 8o degrees'^ while the prevailing wind direction was northwest (Fig. 2). Intermediate photographs indicated that this change in ripple direction was generally gradual, although some severe storms appear-ed to accelerate the process. '■ As a result of these periodic photographic records it appeared desirable to measure quantitatively the amount of change in surface elevation taking place on both a periodic and a seasonal basis. ■199- 9L Fig. 1 Fig. 2 200 EncroaclTment of a shoreward migrating sandbar during the sunmer was destroying large numbers of soft-shell clams (Fig. 3)o By sampling both sides of the bar and the bar itself it was found that there was no survival beyond the forward edge of the bar. The following March the bar was completely leveled by a severe storm (Fig. h) „ It was theorized that by determining quantitatively some of these changes which were going on it might be possible by engineer modification to reduce the nearly 100 per cent mortalities occurring annually in this area. Western Beach hsis prolific sets of soft-shell clams each year, but very few survive to commercial size. Only occasionally are conditions sufficiently favorable, so that there is a limited commercial fishery. Predator mortalities (Polinices) were reported for one year to be nearly 28 per cent (Dow and Wallace, 1950). ' Other mortalities have been attributed largely to hydrogeological changes (Fig. 5)» Green crab damage appears to be rl'egligiT^le- Under the state's combined geological -biological program approximately 33 nia-n days were spent in a partial ground survey of Western Beach. On the basis of a fortnight's work it was estimated that at least 100 man days of field work over a six to eight week period woiild be necessary to provide the minimum data. During this preliminary ground survey, changes in surface conformation and elevation from wind and water erosion and deposition were observed (Fig, 6). It was obvious, then, that a ground survey at best would provide only a composite of daily conditions for the period. To compensate for this deficiency an experiment utilizing ground controlled aerial photography was designed. It was proposed to obtain ail field data on an instantaneous basis, either during one half "tide cycle or during consecutive daylight half -tide cycles. Procedure Preliminary experiments were carried out in May, 1952, using a light ground based plane and a four by five Speed Graphic camera. In addition to the limitations of noncontrolled verticals, weather conditions - — freezing at 5^000 feet, rain at sea level and gusty onshore winds --- did not permit accirrately interpretable results. More carefully organized experiments were carried on between October 9 and 11, 1952, A Fairchild aerial camera mounted in the belly of a multipassenger pontoon plane was used. Weather conditions, except for 10-12 mile per hour southsouthwest winds, were excellent. As in the previous experiments, ground control was exercised by a sixrvey party using a plane table. -201- Fig. 3 202 Fiff. k >'• * ■' J" •el- - -r -> -^4 - -4 Fig. 5 203 Fig. 6 Fig. 7 204 A closed traverse (plane table and telescopic alidade) including all air-ground control panels was commenced October 9j 1952, during the low water period prior to the taking of aerial photographs. The traverse was resumed and closed during the daylight low water period of October 11, 1952. The traverse consisted of 8 legs and 8 occupied stations o Initial Station "A", also used for photographic control and water elevation readings, was reoccupied to close the traverse. The length of traverse was i+,860 feet with a horizontal closure error of minus four feet. Within the traversed area the vertical range was h,kk feet and the vertical closure error was 0,.09 feet. The lateral closure error was not measurable. Simultaneous with the two aerial photographs taken on October 9, vertical readings were made of the water elevation near Station "A". Control was effected by radio communication. When the first photograph was taken at 1233 the elevation of the water was minus 5-35 feet (Fig. T) • The second photograph was taken at 13^5] ^.t this time the water elevation was min\is 2.7^ feet (Fig. 8) . The first photograph was taken at three hours and thirty two minutes from zero low water; the second at four hours and forty four minutes from zero low water. Zero low water was taken from tide tables for Portland, Maine. Plotting Control points on the ground were included in the ground siorvey. Since these same points were visible in the aerial photographs, addi- tional detail, including tide lines, could be accur-ately plotted on the base map (Fig. 9. For purposes of illustration normal computation procedure --data assembled on base groiind survey map --- is reversed). Tide lines which serve as continuous contour lines can be plotted directly from photographs without the inaccuracies nortnally associated with the interpolation of contour's between critical elevations in con- ventional topographic sur\reys. There are several methods by which base map data on the photo- graphs can be combined with data from the groimd survey: (l) by pro- jection of radii tlrirough critical points of control net; (2) by plotting location of critical points in relation to control net and transferring these data to base map, and (3) by superimposing details of photograph on base map and plotting additional data in relation to controls. Resiilts Results of ground control are shown in Table =205- Fig. 8 ^4 ".^r^ ■• Fig. 9 206 Table I. Control Data ' (station "A" - assTJmed elevation minus 3 feet MHW) Station Stadia Elevation (feet) Panel #1 Scarboro River Ferry Rock Panel #2 Panel jfk Panel #5 Panel #6 Panel #7 Stake Station "A" Beacon 1+02 389 165 810 870 520 380 81+5 609 1+20 minios 3 • 63 " 3.26 plus 16.6 minus 5 • 09 5-81 2.76 1.50 1,62 " 5.9^ 2.91 Length of traverse: (1) Stadia - l+,86o.O feet (2) Plotted - l+,861+.0 feet Horizontal closure error - minus h feet Per cent error horizontal closure - O.082 Range of vertical traverse - 1+.1+1+ feet Vertical closure error - minus 0.09 feet Per cent error vertical closure - 2.03 Time and 'elevation: E. S. T. 1233 13^+5 October 9, 1952 Tide Time (from zero low water) +0332 •*-oi+i+i+ Elevation -5.S5 feet -2.7I+ feet -207- Conclusions 1. Satisfactory "base maps can be obtained by means of ground controlled vertical aerial photographs. 2. This is the only method presently available which permits nearly instantaneous measurements . 3. The amount of field work entailed by this type of survey is approximately 10 per cent of that required for conventional ground survey methods . Literature Cited Dow, R. L., and D. E. Wallace. 1950. The story of the Maine clam. Bull. Dept. Sea & Shore Fish., Maine, Sec. 7:22. -208- THE USE OF EQUIPMETW AKD TECMIQUES IN APPLIED SHELLFISH MANAGEMEM' Dana E. Wallace Department of Sea and Shore Fisheries, Augusta, Maine Maine's hard and soft-shell clam fishery is dependent upon natiiral sets, their survival and growth to commercial size, and, in the soft-shell industry, the efficiency with which the clams are har- vested. The following summaries cover projects of the Department of Sea and Shore Fisheries as well as cooperative work with the Fish and Wild- life Service Clam Investigations, and the application of results as carried on with shellfish producing communities = Soft-shell Clam Seed ( Mya ) ' In the soft-shell clam industry our early work was concerned with developing ways of using soft-shell clam seed in an effort to find out if it was economically feasible to transplant from heavy concentrations to commercially depleted areas. At the present time transplanting of Mya is economically unsound o Projects to learn more about predators and their control are continuing and will be reported another year by Fish and Wildlife Service Clam Investigations . Digging Breakage and Mortalities of Soft-shell Clams We find that the present methods of digging in intertidal areas axe extremely wasteful for present and future production of soft-shell clams. This fact has to be considered in any management plans for ovor soft-shell clam industry. It appears that less than one half of the available or potentially available commercial clam, popiolation in Maine ever reaches the consumer. Our work with the commercial diggers in sampling their catch and the flats they have dug Indicate that appro- ximately 20 per cent of the clams are broken in digging and can be considered as lost to the industry. Federal Clam Investigations found that less than one per cent survival v^hen broken in the flats and approximately one half of the unbroken clams remaining in the flats each time the flats are dug died because of depth or position. All of this digging information means that we must try to cut down the frequency of digging of the flats and work out a flexible rotation of areas based upon surveys of area, population, size dis- tribution, growth, and the presence or absence of predators. It is likewise always important in cooperative planning with communities to determine the best time to harvest the clams, considering the biological factors as well as the economics of the fishery and area. -209- Qiialiog- Research Uiilike the soft-shell clam fishery, we have fo'ond that it is definitely economically feasible to transplant q-jahogs, Ven-os mercen- arla . Quahogs of approximately over one half inch in size are relative- ly immiine from green crab damage. They establish themselves in the flats quite readiJy and growth in our areas is exceptionally good as will be reported by Dr., Gustafson in his paper. Gathering Seed aJid Establishing Clam Farms A pumping arrangement is being used to gather seed clams. A dredge consisting of a two inch suction hose connected to a Homelite centrifugal pump rated at 10,000 gallons per hour picks up the water- The unit is portable and weighs only 88 pounds. The water is played through jets do^/m to the flats and the entire dredge is dragged along at approximately 5 to 10 feet a minute. Tiny seed clams in concentra- tions of 200 to 300 per square foot are washed out of the flats. The stream of water picks up the seed clams, the silt and sand is screened out through a one quarter inch mesh screen used on the drag, and jets of water keep the clams moving into xhe dredge and then back into a detachable mesh bag. Very little breakage occurs. The level of the dredge is set with the shoes on the side. Clam Breakage and Mortalities Caused by Digging Soft-shell Clams ( Mya ) On silty clay bottom breakage is quite high. Comments on clam breakage in Maine are part of a paper published by our Department by Dow, Wallace, and Taxiarchis. The degree of breakage of clams varies with the concentration and the range of sizes of clams, as well as with the amoiint of growth and the thiiiness of the shells. Even in sediments in which a high percentage of breakage occurs, careful and experienced diggers have kept the breakage below 10 per cent. In our studies along the coast, five of the ^7 diggers had less than 10 per cent breakage. Two of these dug under good flat conditions while three dug under flat conditions ranging from fair to very poor. The breakage varies both geographically and seasonally. Digging with a hoe produces about 19 per cent breakage, and with a shovel breakage may be cut down to approximately 9 pei" cent. With a shovel a much larger piece of the flats is turned over, increasing efficiency as well as lessening breakage of clams - Dredging Quahogs With the Veniis M, bearing an eight inch discharge hose and mounted on a barge, we were able to get 256 btishels on one day whereas -210- the carrying capacity of the barge alone was about 110 bushels. These quahogs averaged slightly over an inch in size and were compacted in the flats anywhere from 200 to i+00 per square foot. One such area covered three to four acres. Already approximately U,200 bxishels have been transplanted from this area with 3,000 bushels being moved by the Venus M. At least 10,000 bushels have yet to be moved. Quahogs are being taken into conservation areas and spread out by sifting them over the sides of the boats or shoveling them as we do from the barge when planting. In one area quahogs are being left to grow to chowder size. Quahogs are screened over one half inch mesh hard- ware cloth and most of the water is discharged through scuppers on the side of the craft. The rate of discharge of quahogs varied from one to six bushels per minute; however, over an entire tidal operation of approximately four hours, it averaged out to about a bushel a minute- This is in the order of approximately 2,800 seed quahogs each minute that are pumped from the flats. The six inch suction hose passes to the centrifugal pump where the design of the impeller allows the tiny seed quahogs to go through tte pump unharmed and out the discharge hose. -211- REPORT OE CERTAIN PHASES OF THE CHIITCOTEAGUE BAY liWESTIGATIONS M, F. ¥. Sieling Department of Reseaxch and Education, Solomons, Maryland This is a report on progress made on an ecological survey directed toward, among other things, the re -establishment of the oyster industry in the Maryland part of the Chincoteague Bay area. It will discuss primarily problems encountered in planting shells for the purpose of establishing potential seed areas. This survey was begun in 1951 and a brief progress report was made to this group in 1952. Since that time progress has been made along several lines. The area studied runs from Fenwick Island, Delaware, to Chincoteague Inlet, Virginia, and includes Asawoman Bay, Isle of Wight Bay, Sinepuxent Bay, and Chincoteague Bay. This is a contin- uous body of viater and is served from the ocean by two inlets located at Ocean City, Maryland, and at Chincoteague, Virginia. Wo actual barriers exist between the different bays. The physical aspects and the history of the area were given in the 1952 report and will not be repeated here . The hydrography of the area has been studied during the course of the survey and the data will be published elsewhere. However, it might be said very briefly here that the temperature shows a very slight vertical gradient throughout the area except at the inlets where it may be as great as 3-^ C. Throughout most of the area the gradient is not more than 1°C. The horizontal gradient is usually much greater and during the summer varies from the inlets where the ocean water is cooler to the center of the bay where the water is vrarmer. During the winter this pattern is reversed and the water is warmer toward the inle'cs and colder in the center of the bay where the shallow water cools more rapidly. Salinities also show a slight vertical gradient but a marked horizontal gradient from the center of the bay -co the inlets . In the summer salinities are higher in the center of the bay due to the smal]. land drainage ai-ea and the high evaporation in the shallow water™ Salinities decrease toward the inlets where the tidal surge brings nearly piire ocean water into the inlets. During the winter and spring this patter is reversed and higher salinities occiir in the inlets and drop in the central part of the bay due to the lower evaporation rate and increased rainfall during that part of the year. There is no great tidal movement except at the inlets, the tidal amplitude there normally being about three feet, and about one foot in the center of the bay. Currents through- out the bay are of no great magnitude but may have some influence in distributing shellfish larvae throughout the area. -212- During the course of the investigation about 12,000 bushels of shells have been planted annually throughout the area in small test plantings. These plantings, averaging about 2,000 bushels each, have been placed in locations which were selected on the basis of findings from our test shells and on advice from oyster planters in the local areas. In most parts of the area, however, fouling of the shells has been a major factor in the success or failijre of the plantings. Consequently, considerable attention has been given to determining the period of attachment of the common fo-oling organisms which cause trouble on the shell plantings and which were \mknown for this area- One of these organisms in particiilar, the serpiilld wonn (Hydroides), has been more trouble than the others. Its setting period nearly coincides with that of oysters in the area« The worms can cover a shell with a coating of their calcareous tubes in about two weeks- After this occurs there is no hope of a young oyster ever attaching to the shell since this coating becomes thicker as the colony of woi-ms becomes older. These animals set in greater numbers in certain sections of the bay than they do in other parts. Anomia, barnacles, bryozoans, and Crepidula are some of the other major foul- ing organisms present. Serpiilid worms have a definite pattern of setting in the bay which appears to be tied in with the temperature gradient of the water. They set with much less intensity near the inlets and their setting starts there later than it does in the central part of the area. In the central part of the region they begin to set about the middle of May in most years and continue setting with increasing intensity until about the middle of August and then begin to decline slightly. There is then a period of much less setting intensity until about the last week in September when there is again a slight increase in setting and then a complete cessation of setting which occurs about the first week in October,, Wear the inlets the initial set occurs aibout the middle of June and continues with a slight dip in intensity in Aug\ist, and an uptiirn at the end of September which terminates about the middle of October. Setting is also much more intense in areas where there is little tidal movement, thus suggesting that there is also a con- nection between intensity of setting and water movement. For example, the set in areas where there is very slight tidal movement was as high as 1,077 worms per 10 shells in ih days exposure, whereas the set near the inlets was in no case OArer 300 worms per 10 shells for that same period of time. Throughout the central part of Chincoteague Bay the set of these worms through the months of July and August was con- siderably greater than 3OO worms per 10 shells at all stations- Shells planted on the bottom in the central portion of the area were covered with worm tubes in three weel^ so that it became impossible for the oyster larvae to attach. Planting cultch at a time to avoid this set of worms is also impossible in this central part of the bay as the oyster set \:isually occ"'jrs at the height of the set of the serpulids- -213- Barnacles are not a serious fouling organism in most of the area as their setting season is more sharply defined, and cultch may be planted at such a time as to avoid _a heavy set of this organism. In several sections of the area they do set in great numbers in late May and early June but this does not interfere with oyster setting as shells can be planted after that time. Near the inlets the set of barnacles is usually later and lighter and extends over a longer period of time than it does in the central paxt of the bay. Also, oyster drills which are numerous in the area kill great numbers of these before the oysters begin to set. Bryozoa are not too serious a pest in the Chincoteague Bay region as they set sparsely. There are several different species which are common but none is as abundant as in Chesapeake Bay, and they do not form the thick crust on shells commonly observed in that area. Crepidula is not a serious fouling organism iji the area as its setting period is rather long, but the number of indiiriduals is small, so that it has not created a problem as yet. These occur more fre- quently near the inlets than in the central part of the bay. Anomia is a much more serious fouling agent in some parts of the area as it sets at the same time as the oyster larvae and it grows much faster, thus overgrowing young oysters. At certain times Anomia may completely cover a shell and any other organisms thereon in about a month after attachment. They are a very serious problem in the best potential seed area which has been located to date. Other fouling organisms are not dangerous and in most cases do not set in large enough numbers to be of any significance in a shell planting program. The part of the program which has had as its aim the rehabil- itation of the oyster industry in the Maryland part of the area has been conducted with the goal of producing seed locally for the planters. Small plantings of shells made in several different parts of the bay, losually about 2,0C0 bushels each, have given varied results. Some of these plantings were made with plantings of brood stock oysters in the immediate area and others were made near private plantings of oysters to take advantage of the spawn from them. Very little success was ex- perienced where the plantings had small lots of brocd stock oysters in the midst of them. It is believed that too few oysters were used in the plantings, since where the cultch was near large private plantings of oysters the set of oysters was moderately successful. Two different methods of planting shells have been used in the bay: near the inlet at Ocean City the shells have been planted on the tidal flats in windrows and in the deeper parts of the bay the shells -2ll+- •were 'broadcast on the 'bottom. The plantings made near the Ocean City- inlet were planted in long windrows on the tidal flats so that they were exposed on each low tide. These have "been moderately successful, having a set averaging about 300 spat per 'bushel at the end of the setting season. However, the 'bottom is mostly sand and due to a heavy storm diiring the fall, approximately half of the shells were covered with sajid. Some which were planted some little distance from the inlet were not covered 'but received a very light set so that their value is slight. These plantings were made over the last two years. This year a different region near the inlet which has a muddy 'bottom and does not completely eb'b out on low tide was planted. It is hoped that there the bottom will not shift and cover the shells. Fouling in the Ocean City area on the flats is not serious but it is not known how it will be on these shells which will not be exposed each day. Test shells diiring the past two years have shown some foulingj jparticularly by Bryozoa. Survival of spat is very good in that section and it is hoped that a seed area similar to that in the ■Virginia Seaside may be established there. In the deeper parts of the bay where the shells are broadcast on the bottom varying degrees of success have been experienced. Several factors have contributed to the failures, the main one being the heavy fouling already mentioned, and the other being the lack of oyster brood stock in many parts of the area. In those areas where there was no brood stock about 200 bushels of mature oysters were planted in the spring in the spot selected to be planted with shells. This was done early in order that they would become acclimated before the onset of the spawning season. Late in J\me the shells were planted on and around these oysters. A light set resulted on those shells which were among and very close to the brood stock, 'but none on those which were 50d :£teet away from the oysters. There were no other oysters in any direction from these plantings for several miles and in this one area the tidal movement was very slight, so that there was no other so\irce of spawn. Fouling by serpulid worms in this region was particularly heavy so that three weeks after the shells were planted they were completely covered with the worm tubes . It appears that here the 200 bushels of brood stock were not adequate to give a set and also that larvae did not move very far away from the parent oysters. Test shells placed in a pattern around this planting failed to pick up any spat even a -quai-ter of a mile away from the brood stock oysters. Other plantings placed near large commercial oyster beds re- ceived moderate sets. Some of these shells, however, were covered with fouling organisms within a very short time and had practically no surviving spat. One planting, however, located just a short distance above the 'Virginia line, received a good commercial set and at the end of the season gave a spat count of 900 per bushel. This planting came through the winter and still had a count of TOO spat per bushel this spring. This is the only area which gave a really good -215- set and its location takes advantage of the great number of oysters which are planted in Virginia, The tide which comes in through the Chincoteague Inlet carries larvae from the Virginia oysters into Maryland where they set. In addition there are several large ^eds of oysters in Maryland not too far from the shell planting. This is an area which does not get a heavy set of serpulid worms but does receive a heavy set of Anomia . The set of these coincides with that of oysters and so they cannot Tae avoided when planting shells - They also grow faster than oysters and so may overgrow them and cause considerable mortality among the young spat. Ftirther they cover a large percentage of the shell surface and so reduce the efficiency of the shells. If there were intertidal areas in that part of the bay we would have much less fouling on the shells and consequently better sets. However, in Maryland there are no such areas as are found in Virginia, where the set is good and the foul- ing is negligible. It is believed that once a good popxilation of oysters is established in the area, sets will be better and the seed program could be extended. Many very small areas now give good sets but are too small to be of practical use. The two coitmon oyster drills or screwborers are very numerous in the bay and cause considerable loss to the planters killing great numbers of spat at an early age. This of course is a big factor in the survival of a set which may occur and it is hoped that a program of drill control can be initiated in the near future. The future of the Industry in the area depends upon the control of drills and a soiorce of good seed oysters. -216- COMPUTATION OF OYSTER YIELDS IN VIRGINIA * J. L. McHugh and J. D. Andrews Virginia Fisheries Laboratory, Gloucester point, Virginia Drs. Andrews and Hewatt have teen holding oysters in trays sus- pended from the Virginia Fisheries Laboratory pier at Gloucester Point, Virginia, for the past four years. The primary objective has been to study mortality rates, but other information has been gatliered from time to time, particularly on the growth rate. D-aring the course of these investigations we have been impressed by the yields that have been ob- tained, for it has not been uncommon to realize three bushels of market- sized oysters for each original bushel of seed placed in the trays. Reduced to the simplest terms, the yield of market oysters from planted seed is detenained by the interaction of grovth and mortality. This has been pointed out by Hopkins and Menzel (1952);, who have outlined methods by which planters can detennine growth and mortality rates from which they can calciilate the net yield. Owen (1953) has described the relationship between growth, mortality, and yield at given locations in Louisiana waters, using figures obtained from experimental plants of seed. Thus, our work is not original in the sense that it represents a new approach. It is original, however, to the extent that it concerns the Chesapeake Bay region, and that it utilizes the methods of computation applied to fish populations by Ricker (l9'+5j 19^8) and others. Hewatt and Andrews (195^+) have presented extensive data on oyster mortalities in trays at Gloucester Point, Virginia, and information on oyster growth is accumulating. Both items of information are available in some detail, for mortality records were made daily in summer and at intervals of 10 days to two weeks in winter, and growth measurements have been made at intervals of two weeks to one month. Oystermeh usually report that planted grounds in Chesapeake Bay yield about one bushel of market oysters for each bushel of seed planted. The crop is har\^ested two to fo\rr years after planting, depending on the characteristics of the particular piece of gro^ond^ usually determined through past experience or by occasional sampling j, and based on the size of the oysters. It is relatively simple to calcula,te the mortality tha.t occurs between planting and harvestingo A bushel of seed oysters from Wreck Shoal in the James River may contain as many as 3,000 oysters of various sizes » If he coimts a sample of seed, the planter will ignore the small spat, for he knows that these tiny oysters will not s-orvive the planting operations, or if they do, will fall prey to oyster drills and other enemies shortly after, and hence cannot contribute to the harvesto The * Contributions from the Virginia Fisheries Laboratory, KOo 55« -217= planter, therefore, will conclude that the viable seed in each bushel number perhaps 1,000 or 1,200 at the most. The market oysters that he harvests in an average period of three years will run aljout 300 to each bushel. Therefore, when the yield is 1:1, about 900 of the original 1,200 oysters, or 75 per cent of the number planted, will have been lost. The true mortality, based on all the oysters in the original planting, is of the order of 90 per cent, but the lower figure is more realistic from the oysterman's point of view. On first thought, it might seem that a mortality of 75 per cent in three years is equivalent to a death rate of 25 per cent per year. Percentages cannot be s^jmmed or divided so simply, however, and actually the annual rate is considerably higher. It can be demonstrated simply that an annual death rate of 37 per cent will produce a total mortality of 75 per cent in tliree years, by applying this annual rate to a group of 100 oysters, as follows: Original number Subtract 37 per cent Survivors Subtract 37 per cent Survivors Subtract 37 per cent Survivors = 100 37 = 63 (End of first year) 23 UO (End of second year) 15 25 (End of third year) Total survival rate « 25 per cent Total mortality rate = 75 per cent Mathematically, the conversion of short period observations on mortality or growth rates to annual rates is somewhat complicated. For- tunately these calculations have been made and recorded systematically in tables (Ricker, 19^4-8) from which mortality rates on a percentage basis can be converted to instantaneous rates, which can be summed- directly. The Rate of Growth in Length Growth rates were measured on oysters held in trays at the Vir- ginia Fisheries Laboratory pier. The most extensive data were available on the rate of growth in length, hence length was used in setting up the basic growth curves (Fig. l). The curves in Figure 1 were obtained by grouping data from various trays of oysters according to their average -218- Af>r May June July Aug Sepf Ocf M)y Dec Jsn Feb Mar Fig. 1. Average growth rates of oysters in trays at Gloucester Point, Virginia. The data were grouped into broad categories based on the average length in April, which marks approximately the beginning of the year's growth. The points on which the successive curves were based are indicated alternately as black and open circles for ease in recog- nition. 219 length at the "beginning of April, the approximate time at which the year's gro-wth coinmences» The decision to group -was dictated "by two considerations, namely, that the data were not sufficient to permit grouping according to specific lengths, and that the average process is much more practical from the oysterman's point of view.. From the c^'^ves in Figure 1, the lengths at the end of each month were recorded. Figure 2 was then constructed, after the method described by Walford (l9^6), by wiiich the lengths at a pexticijlar date are plotted against the lengths a given time inter-i'-al later, in this case at intervals of one month„ Smooth lines were drawn through each set of points. By reading off lengths from these curves, or by inter- polating between them, the growth in length of oysters in trays at Gloucester Point, starting with any given original size, can be re- constructed easily. The Rate of Growth in Weight The available data on growth in weight at Gloucester Point, though less extensive tlia,n the length records, are adequate to con- struct a graph of the length-weight relationship. Plotted on logarith- mic coordinates the resulting points assume a linear relationship, which can be represented by a line fitted by the method of least squares, as in Figure 3c Weights corresponding to the lengths read off Figure 2 were plotted as in Figure h, which represents the best available average estimate of the growth in weight of Wreck Shoal seed transferred to trays at Gloucester Point. The lower curve in this figure illustrates the growth rate of the small oysters (mostly less than one inch in length) that do not survive planting operations in Chesapeake Bay. The upper curve re- presents the groirth of the larger seed oysters (those recognized as seed by the planters ) o The Instantaneous Rate of Growth The instantaneous growth rate can be computed from the following- e3q)ression (Ricker, 19^5)- e^ - 1 ^ b where e - 2.7l83jr the base of the natural logaritlims, k ss the iristantan= ecus growth rate,, and b = the fraction by which the surviving oysters have increased in weight during the period in question. For the present piii^pose, however j, the computations can be present- ed more simply by the method outlined by Ricker and Foerster {l9hQ) , as -220- / Z 3 too I 20 30 40 SO €0 70 80 90 /OO NO Length in mithmeters on AprN / Fig. 2. Growth curves for oysters held in trays at Gloucester Point, Virginia, trans- formed according to the method of Walford (19^6) 221 0.4 / Z /nches 3 4 S 6 ■10.0 BO e.o so 4.0 - 3.0 2.0 /.s — ID X ^ ^ I - o.s Hi -o.z — o./ 20 30 40 60 ao /OO /SO 200 Average /engf-h //? mi//ime/-ers 0.04 300 Fig. 3« The relationship between length and weight in oysters held in trays at Gloucester Point, Va. 222 ONDJfMAMJ JA SOf/DjrMAMJJA SOA/DJ FMAMJ JA SO Months Fig. h. Seasonal patterns of growth in weight of oysters held in trajrs at Gloucester Point. The lower curve represents the growth of the current year spat in seed oysters from Wreck Shoal in the James River, which do not survive when transplant- ed to Chesapeake Bay. The upper ciorve represents the thick- shelled larger oysters in Wreck Shoal seed, that are recognized as seed by the planters . 223 illustrated in Table lo The i:istanta:ieo"as growth rates k were computed "by dividing the values in the previous columrx by Co43^3/ "the logarithm ol e. The Mortality Rate As demonstrated by Eewatt and Andrews (19?^) y the mortality of oysters in trays at Gloucester Point is concentrated for the most' part in the summer months (ji-ily to October inclusive)., Jrom the original data on which the,ir report was based, the monthly mortality rates have been computed, that is, the percentage of the oysters alive at the be- ginning of each month that died during that month (Figo 5)« The Instantaneous Rate of Mortality The instantaneous mortality rate can be computed, as was the instantaneous growth rate, from a similar form-'ola (Ricker, 19^5) • e a 1 - a where e - 2.7l83;> 2. " ^^® instantaneous nati:iral mortality rate in trayg at Gloucester Point, and a = the fraction of the original number of oysters that died during the period under consideration (usually a signifies the annual rate)« Here again it is simpler to use Ricker 's (l9^8) table to read off the corresponding values directly, according to the value of a. The instantaneous rates listed in Tables II and IH were obtained by this method o Computation of Yields The instantaneous rates of growth and mortality were combined, as in Tables II and III, 'uO calculate the net increase in total mass of oysters (k - q). Thj£ corresponding changes in biomass (total volumes of oysters) were read from column 12 (if positive) or from column 2 (if negative) in Ricker 's (l9^) appendix table » Assigning the arbi- trary value ICO to the original volume of oysters planted, the relative biomass at the end of each month was computed. The absolute volume of oysters in 100 bushels of seed was then calculated, and this value was substituted for the original arbitrary value of lOOo The subsequent absolute biomass at the end of each month after planting was derived by simple proportion. .22if- ^ ^ § ^ S 8 8 <::i «:S ^ <:i Q Q Qi •H 225 Table 11 presents these computations as applied to the current year spat in 100 bushels of Wreck Shoal seed. The increase in biomass is very large, reaching l68 times the original volume at the end of 33 months^ when this group reached its greatest computed yield. The original volume of these oysters is relatively small^ ho-/fever^ being only one-half bushel for each 100 b^lshels of seeda Consequently, this tremendous increase in biomass produces a maximijm cf only 84 bushels of market oysters for e3.ch 100 bushels of seed. It must be pointed out that these figizres are only approximations, for the original estimate of OoS b-oshels in each 100 bushels of seed was derived from the average length of these oysters,. It is probable that this represents an over- estimate rather than a low figure^ thus the maximum volume may be too higho Nevertheless, this group of small seed oysters probably con- tributes significantly to the higher yields obtained by planters in the upper estuaries, wtere drills are not a problem. In Table III the same computations are applied to the group of larger oysters in Wreck Shoal seed, recognized as usefiil seed by the planters. Here, although the maximiim vol\jme, reached in 22 months, is only about five times that of the original planting, the oysters when planted make up about half the entire volume of seed. Thus, a yield of about 2.5 bushels is possible from the larger oysters in each original bushel of seed. Ajiother consideration must be introduced in combining these two sets of figixres to derive the total yield. At planting, few, if any, of the oysters are of market size, and our growth studies have shown that some of the survivors may never reach the arbitrary length of three inches or over that we have used to designate market oysters. Allowance has been made for the size factor in computing the yields in Table IV. It will be noted that two maxima in the yield of market- sized oysters are reached, the first, of about 2.8 bushels for one, in 22 months after planting, and the second, of about 2.9 bushels for one, in 3^ months. The slightly larger value for the second maximum pro- bably is not si.gniJTicant, and the greater total volume of oysters in existence at 22 months (see column h) would aJjnost certainly contain signlfican.t numbers smaller thaji three inches worth shucking so as to boost the computed yield. Applications to Oyster Planting The yields discussed above are illustrated graphically in Figure 6. Obviously, it is not wise to apply results obtained from tray cul- ture directly to practical oyster ing problems, at least without attempt- ing to determine how these rates of growth and mortality compare with those on planted grounds . Considering first the growth rate, it is fairly certain that the seasonal variations observed in trays are similar in order of time. -226- 0/^OJFJ^AMJJ/iSO///}jrjHAMJJAS0A/OJPAlAAlJJAS0/^D Fig. 6. The yield, in bushels of live oysters, in successive months after planting in trays at Gloucester Point, Virginia, from Wreck Shoal seed. The upper curve represents all oysters, including the current year spat. It must be noted that the original yield at planting is only about one-half the actual bulk of the seed, because each bushel of seed oysters contains about half a bushel of shell, to which the oysters are attached, and fouling organisms. The three lower curves represent respectively the yield of oysters larger than three inches in length from the entire vol\jme of seed, from the larger seed oysters, and from the current year spat. 227 if not li: mag3ii'j.4.£j,- to gcow^ih cxa pianted gro'ai}d,o It can te asB'umed aiso^ thac ]~esa'UBe the tra;^fB ai~e exposed, to a mare effacx.i've cii'^ culatioii of ■m.tSTrf aad ■beeau£& there is relatively less silt to "be x'ejee.ted, ogBtsrs ie. trajs ■ji.'ill grow faster thar. those on the -bc>ttom„ ThlB appears to Le supporrted Jij the ara3I.able data^, arjd. ve hope to fiibtala 'bette:^" data soos... ■j.'he seasonal pattcirn cf mortality rates in trays at Gloucester Point, appears to 'bear a -close relatioiLShip to the seasosal eyele cf ■water teiEpBratore (Heifatt aad. A:3dre-tr6j, 195^)° Therefore^ for the sou'^ces of mortality x,o whiah tray oiystern are suijeetj, it wo'dld not appi^ar 'linreasoEisilblt' to ass;jme -tbat a simiiap mortality patt-ern ■K'oiild applj- on plant.ed 'i30bz:jm.j with respect to time though ncit necessar'ily in magnitudeo Oysters on the bottom^ however^ are subject to death from oT.her important causeSj, the depredations of drills or screwborers being perhaps the principal factor. iJnpublished obser^irardons of oyster dcili activity in the vicinity of Gloucester Pjinx sho*; that the activity of these predators is closely associated, with the tempt:ratare cycle^ and these oTjser-v'ations can reascnalil;y be extemed to cc;-*er the ac-ti-vities ' of other prrtdatore^ all of vhich are cold blooded and thus qui.te sensi= tive to temperature variations o Thus it seems sai.'e to assume that the aTe.rage seasonal pattern of mortality on the bottom is similar to the patbe.rn obseirved, in trays <> Hews-tt axdi Andreses (l95^) report annual mortalities of a:bout 25 per cent for oysters in trays at Gloucester Fointj, but the calcuLations made earlier in the present paper suggest that the annual mmrtall.ity on the bottom i.6 of the order of 37 pt;'^" cento The annual mortality rate asBOv'iated with bottom factors;, therefore, is about 16 per cento This suggests ihat the fungus I/ermocystidi'-im marinum is a more serious source cf mortality than the oyster drilly at least insofar as the larger seed oysters are conceraed. There sec-5ms to be good i-eason to beli.eve that gro'wfch ard mcr= tali-fcy on planted bot-'iom differ from the same rates in trays chiefly la magnitude sfather than ±a seasoaal pattern. Thus^ eurres sho'Wing the yield ol. plairted ground at vario'as levels of grorbh aisd mortality can be construetsd by adjusting by appropriate factors the rates deter= minad. from tray culture o B'uch a series of curves^ l>ased on a gro'srth "rate three =qviaji-c.ers ay. great as the rate in trays.^, is illustrated in Figure 'Jo It is worth rotlng that the mas;imum yield^ uoless mortality is except ioBa.lly luWy is reacbsid about a year and. a haH;' after plantingo If these oysters we^ro Hiut hax'rest.ed until fall^ a mj^rs three or four months after the maximsan yield was reached^ the yield would have fallen cojisiderably^ arid. al-th,jugh the sprin^g growt.h of the foHo"i5"i;ng year ■would cause the yield to increase agaln^ it >«'ould. never appare'ntly reach the fo-jTiner -lerel. Families of carreB^ baBed on various rafcc-is cf gro-*rth ana mortality^ can. be eoSiStructed read.Hy« The oysterman can determlL,e the rates ehar= acteristic of hi.6 gro-unds by method.s described by HopMus and Me;:r-^el =228.= zoo Of^DJfMAMJJA SOHDJFMAMJJA SOMDJ/'MAMJJA SO//J> Fig. 7« Hypothetical yield curves, based on grovth rate three-quarters as rapid (0.75k) as the Yate in trays at Gloucester Point, Virginia, and at mortality rates equal to one-half, one, one and one-half, and two times (0.5q, q, 1.5q^ and 2q) the rate in trays. The figures within the arrows represent the number of oysters per bushel. 229 •19?'^) s ^-'-^ ^y seleciiiiig the appropriate e-orve, can detei^^iiae vhen to liarTest for the gi.*eatest yield, iri. li-ushsls of oysters » ^he Bushel Count It ■wo'-old loe of little 'beriaf it to the planter if he VETe to harvest his oysters at the point of maximum yield;, ooly to f Ir^d that the slse was to;: small for eco:aomieal shucki:ago The oyBtennan's criterion of size is the eouxit per bushel,, and it is -asefui to kciow the relationship bet-iireen the average lezigth^ or average weight of oys tiers ;, arid the bushel count o By actual measure of oysters cf yarioiis sises^ grown Ir. traya at Gloucester Po;iiit, we ha^re found that the relationships between both length and weight with yield^ can be expressed as straight lines on logarithmic coordinates j, as with the laTj.gth-=weight relationship in Figure ko Furthermore^ the re- lationship of weight to yield can be expressed roughly t.y an even simpler ejcpi^ession; (3 X 10^) w where a is the number of oysters per bushel, and w is the average weight of the oysters in grams. In Figure 7 "the counts per bushel at the points of inflection are given as nimljerB within arrows at the appropriate positions » Is Further Investigation Necessary? Several factors important to the oystermaii have beer, ignored f-T!. the preceding sections o Perhaps the most important is the question: "Are bhe oysters in prime cor-dition at the time ol maximum yieid^ aL'.d is the shucking ratio high?" The planter is pe.rhap3 better able than ttie biologist to answer this quest iono The producer will also be interested in the demarjd and the price p for he may find it necessary often to ho,ld his crop past the point of TEfi>x:unufli yield whether he wishes to or noto Some practical considerations such as the labor supply j, will tend to force him to spread his operations over as ma"::.y months as possible | others j, such as the ne'jessity to obtain high fields,, favor a co.a.eentration of effort. Technological developments that would eliminate such conflicting pres= sureSp such .as the discovery of mechanical shucking methods and the development of quick freezing processes, seem to offer "cha best hope for solution of these problems. =230= Much more accurate information is necessary on the growth and mortality rates characteristic of planted bottomo It is hoped to get this information in two ways, by examining representative samples from planted grounds in various areas of the Bay axid estuaries, and by experimental plantings of marked oysters. We hope also that some planters will be stimulated by these findings to examine our f igiires carefully. If our argument appears reasonable, we would, urge them to experiment by harvesting at various time intervals. It goes with= out saying that for maximum resiilts, such experimentation should be planned carefully and should be accompanied by carefilL and systematic recording. The Virginia Fisheries Laboratory will be willing and anxious to cooperate in such experiments. =■231- Literature Cited Hewatt, Willis G., and Jay E. Andrews. 195^- Oyster mortality studies in Virginia. I. Mortalities of oysters in trays at Gloucester Point, York River. Texas Jr. Sci. 6(2): I2I-I33. Hopkins, Sewell H. , and R. W. Menzel. 1952. How to decide best time to harvest oyster crops. Atlantic Fisherman 33(9) Oct. 1952: 15, 36-37. Owen, H. Malcolm. 1953° Growth and mortality of oysters in Louisiana. Bull. Mar. Sci. Gulf & Carib. 3(1): ^+4-5^+. Ricker, William E. 19^5- A method of estimating minimum size limits for obtaining the maximum yield. Copeia 19^5(2): 8^-9^. Ricker, William E. 19^8- Methods of estimating vital statistics of fish populations. Indiana Univ. Publ., Science Ser. I5. Bloomington, Indiana, v 101 pp. Ricker, William E., and R. E. Foerster. 19^8. Computation of fish production. Bull. Bingham Ocean. Coll. ll(4): 173-211. WaJ-ford, Lionel A. 19^6. A new graphic method of describing the growth of animals. Biol. Bull. 90 (2 ): 1^+1-1^+7- -232- TABLE I Computation of seasonal growth rates for Wreck Shoal seed oysters transferred to trays at Gloucester Point. The lengths are inserted for reference, and are not used in the computations. Current Year Spat 1 One year of age or o Ider Beginning of month Length in mm. Logio weight in gms, Diff- erence k Length in mm. Log 10 weight in gms. Diff- erence k October 12 -0.43 0.30 0.69 48 1.22 0.13 0.30 November 15 -0.13 0.21 0.48 54 1.35 0.11 0.25 December 18 + 0.08 0.06 0.14 59 1.46 0.03 0.07 January 19 0.14 0.05 0.12 60 1.49 0,00 0.00 February 20 0.19 0.00 0.00 60 1.49 0.00 0.00 ' March 20 0.19 0.05 0.12 60 1.49 0.00 0.00 April 21 0.24 0.11 0.25 60 1.49 0.08 0. 18 May 23 0.35 0.38 0.88 64 1.57 0.08 0.18 June 32 0.73 0.27 0.62 69 1.65 0.08 0. 18 July 40 1.00 0.19 0.44 74 1.73 0.05 0.12 August 47 1. 19 0.13 0.30 78 1.78 0.06 0.14 September 53 1.32 0.11 0.25 81 1.84 0.03 0.07 October 58 1.43 0.11 0.25 84 1.87 0.03 0.07 November 63 1.54 0.08 0.18 86 1.90 0.03 0.07 December 67 1.62 0.02 0.05 89 1.93 0.01 0.02 January 68 1.64 0.01 0.02 90 1.94 0.03 0.07 February 69 1.65 91 1.97 0.00 0.00 » 0.00 0.00 March* 70 1.65 0.00 0.00 ■ 92 1.97 0.00 0.00 ■233- TABLE I (continued) Current Year Spat One year of age or o Ider Beginning of Length Logio weight Diff- k Length weight Diff- k month in mm. in gms. erence in mm. in gms. erence April 70 1.65 0.08 0.18 92 1,97 0.03 0.07 May 74 1.73 0.06 0. 14 94 2,00 0.05 0.12 June 78 1.79 0.05 0.12 97 2.05 0,03 0.07 July 82 1.84 0.03 0.07 100 2.08 0,03 0.07 August 86 1.87 0.03 0,07 102 2.11 0.01 0,02 Septeinber 88 1.90 0.03 0.07 103 2.12 0.01 0.02 October 90 1.93 0.04 0.09 104 2.13 0.00 0.00 November 92 1.97 0.03 0,07 105 2,13 0,00 0.00 December 94 2.00 0.01 0.02 105 2,13 0.00 0,00 January 95 2.01 0.01 0.02 106 2. 13 0.00 0,00 February 95 2.02 0.01 0.02 106 2, 13 0,00 0,00 March 96 2.03 0.01 0.02 106 2,13 0.00 0,00 April 96 2,04. 0.01 0,02 106 2,13 0.00 0.00 May 98 2.05 0.03 0.07 106 2. 13 0.03 0.07 June 101 2.08 0,03 0.07 107 2. 16 0.01 0.02 July- 103 2.11 108 2.17 » . 0.01 0.02 0,02 0.05 August 105 2,12 109 2,19 . 0.01 0.02- 0.00 0.00 September 106 2.13 0,01 0,02 109 2,19 0.00 0.00 October 106 2.14 110 2,19 0.01 0.02 0.00 0.00 Novennber 106 2.15 0.01 0.02 110 2.19 0.00 0,00 Decennber 107 2,16 { 110 2.19 -234- TABLE II Computation of relative biomass, and absolute biomass per original bushel of seed oysters, for the current-year spat in Wreck Shoal seed. Beginning of month k q k- q Change in Eiomass Biomass Absolute bionnass per 100 bu. of seed October 100 0.5 0.69 0.01 0.68 + 0.97 November 197 1.0 0.48 0.00 0.48 + 0.61 December 317 1.6 0. 14 0.00 0. 14 + 0. 15 January 365 1.8 0. 12 0.01 0. 11 + 0.12 February 409 2.0 0.00 0.00 0.00 0,00 March 409 2.0 0.12 0.01 0.11 + 0.12 April 457 2.3 0.25 0.00 0.25 + 0.28 May 585 2.9 0.88 0.01 0.87 + 1.39 June 1,398 7.0 0.62 0.02 0.60 + 0.82 July 2,544 12.7 0.44 0.03 0.41 + 0.51 August 3,841 19.2 0.30 0.08 0.22 + 0.25 September 4,801 24.0 0.25 0.08 0.17 + 0. 18 October 5,665 28.3 0.25 0.03 0.22 + 0.25 November 7,081 35.4 0. 18 0.01 0.17 + 0. 18 December 8,356 41.8 0.05 0.00 0.05 + 0.05 January 8,774 43.9 0.02 0.00 0.02 + 0.02 February 8, 943 44.7 0.00 0.00 0.00 0.00 March 8,948 44.7 0.00 0.00 0,00 0.00 April 8,948 44.7 0. 18 0.00 0.18 + 0.19 -235- TABLE II (continued) Beginning Change Absolute biomass of k q k - q in Biomass per 100 bu. month BiomasB of seed May 10,648 53.2 0.14 0.01 0.13 + 0.14 June 12.139 60.7 0.12 0.02 0.10 + 0.10 • July 13,353 66.8 0.07 0,06 O.OI + 0.01 August 13,486 67.4 0.07 0. 12 -0.05 -0.05 September 12,812 64. 1 0.07 0. 10 -0,03 -0.03 October 12.428 62.1 0.09 0.04 0.05 + 0.05 November 13,049 65.2 0.07 0.01 0.06 + 0,06 December 13.832 69.2 0.02 0.00 0.02 + 0.02 January 14,109 70.5 0.02 0.01 0.01 + 0.01 February 14,250 71.2 0.02 0.00 0.02 + 0.02 March 14,535 72.7 0.02 0.00 0.02 + 0.02 April 14,826 74.1 0.02 0.00 0.02 + 0.02 May 15,122 75,6 0.07 0.01 0.06 + 0.06 June 16,029 80.1 0.07 0.02 0.05 + 0.05 July 16,830 84.2 0.02 0.04 -0.02 -0.02 August 16,493 82.5 0.02 0. 12 -0. 10 -0. 10 Septennber 14, 844 74.2 0.02 0. 16 -0.14 -0. 13 October 12.914 64.6 0.02 0.05 -0.03 -0.03 November 12,526 62.6 0.02 0.02 0.00 0.00 December 0.00 12,526 62.6 ■236- TABLE III Computation of relative biomasa, and absolute biomass per original bushel of seed oyatere, for the yearling and older oysters in Wreck Shoal seed. Beginning of month Change k - q in Biomass Biomass Absolute biomass per 100 bu. of seed October 100 50 0.30 0.01 + 0.29 + 0.34 November 134 67 0.25 0.00 + 0.25 + 0.28 December 172 86 0.07 0.00 + 0.07 + 0.07 January 184 92 0.00 O.OI -0.01 -0.01 February 182 91 0.00 0.00 0.00 0.00 March 182 91 0.00 0.01 -0.01 -0.01 April 180 90 0. 18 0.00 + 0.18 + 0.19 May 214 107 0. 18 0.01 + 0.17 +0.18 June 252 126 0.18 0.02 + 0.16 + 0.17 July 295 148 0. IE 0.03 + 0.09 + 0.09 August 322 161 0.14 0.08 + 0.06 + 0.06 September 341 170 0.07 0.08 -0.01 -0.01 October 338 169 0.07 0.03 + 0.04 + 0.04 November 352 176 0.07 0,01 + 0.06 + 0.06 December 373 186 0.02 0.00 + 0.02 + 0.02 .January 380 190 0.07 0.00 + 0.07 + 0.07 February 407 204 0.00 0.00 0.00 0.00 March 407 204 0.00 0.00 0.00 0.00 April 407 204 0.07 0.00 + 0.07 + 0.07 -237- TABLE III (continued) Beginning of month k q k-q Change in Biomass Biomass Absolute biomass per 100 bu. of seed May 435 218 0. 12 0.01 + 0.11 + 0.12 June 487 244 0.07 0.02 + 0.05 + 0.05 • July 511 256 0.07 0.06 + 0.01 + 0.01 August 516 258 0.02 0.12 -0. 10 -0. 10 September 464 232 0.02 0, 10 -0.08 -0.08 ' October 427 214 0.00 0.05 -0.05 -0.05 November 406 203 0.00 0.01 -O.Ol -0.01 December 402 201 0.00 0.00 0.00 0.00 January 402 201 0.00 0.01 -0.01 -0.01 February % 398 199 0.00 0.00 0.00 0.00 March 398 199 0,00 0.00 0.00 0.00 April 398 199 0.00 0.00 0.00 0.00 May 398 199 0.07 0.01 + 0.06 + 0.06 June 422 211 0.02 0.02 0.00 0.00 July 422 211 0.05 0.04 + 0.01 + 0.01 August 426 213 0,00 0. 12 -0. 12 -0. 11 September 375 188 0.00 0. 16 -0.16 -0,15 October 315 158 0.00 0.05 -0.05 -0.05 * November 299 150 0.00 0.02 -0.02 -0.02 December 293 146 -238- TABLE IV Total biomass resulting from the planting of 100 tushels of Wreck Shoal seed in trays at Gloucester Point. Ab solute biomass Percent Beginning of per 100 bu. of seed market per 100 t oysters m.of seed Bushels of m oysters per 1 of seed arket 00 bu. month Spat Young Total Spat Young October 0.5 50 50 12 + 6 = 6 November 1.0 67 68 18 + 12 = 12 December 1.6 86 88 19 + 16 = 16 January- 1.8 92 94 20 + 18 = 18 February 2.0 91 93 20 + 18 = 18 March 2.0 91 93 20 + 18 = 18 April 2.3 90 92 20 + 18 = 18 May 2.9 107 110 1 23 + 25 = 25 June 7.0 126 133 3 31 + 39 = 39 July 12.7 147.5 160 5 38 1 + 56 = 57 August 19.2 161 180 8 41 2 + 66 = 68 September 24.0 170.5 194 14 43 3 + 73 = 76 October 28.3 169 197 19 53 5 + 90 = 95 November 35.4 176 211 21 61 7 + 107 = 114 December 41.8 186.5 228 25 75 10 + 140 = 150 January 43.9 190 234 26 84 11 + 160 = 171 February 44.7 203.5 248 27 85 12 + 173 = 185 March 44.7 203,5 248 28 85 13 + 173 = 186 April 44.7 203.5 248 29 86 , 13 + 175 = 188 May 53.2 217.5 271 31 87 , 16 + 189 = 205 June 60.7 243.5 304 36 90 22 + 219 = 241 July 66.8 255.5 322 40 91 27 + 232 = 259 August 67.4 258 325 55 95 37 + 245 = 282 Septerpber 64.1 232 296 60 95 38 + 220 = 258 October 62.1 213.5 276 70 95 43 + 203 = 246 November 65.2 203 268 75 96 49 + 195 = 244 December 69.2 201 270 80 96 55 + 193 = 248 1 January 70.5 201 272 83 97 58 + 195 = 253 February 71.2 199 270 84 98 60 + 195 = 255 March 72.7 199 272 84 98 61 + 195 = 256 April 74.1 199 273 86 98 64 + 195 = 259 May 75.6 199 275 87 98 66 + 195 = 261 June 80. 1 211 291 90 99 72 + 209 = 281 July 84. 2 211 295 91 99 77 + 209 = 286 August 82.5 213 296 91 100 75 + 213 = 288 Septenber 74.2 188 262 93 100 69 + 188 = 257 October 64.6 158 223 95 100 61 + 158 = 219 November 62.6 150 213 95 100 59 + 150 = 209 December 62.6 146 209 -23 95 9- 100 59 + 146 :. 205 ■ ■ - SHELLFISH SANITATION AS KELAIED TC THE EXPORT ASL :iIPOr:T 7BMJE JH JAKALA J. R. Menzifcs Depai'tmant of Hational Health ar^ Welfare^, ot'oawa, OanacLa Wheii shellfish eaaitation in North Amfcrlca is coneldered, it is not surprising that th5 past thirty ytars must be re-flefCed., No account of shellfish sanitation in JSbrth America woijld te compl^.t-'v withaat re^ ference to the events of late: 1924 a-Td tarly 1925 which are clearly etched on the mfc-TflDrlj&s of l3crf;h producers aad hfcalth officials » The typhoid fever cases then attri^jitecL to the eating of Ehsaifish were vmdoubtedly responsible for most of the control procedures which have since heen developed. It was generally agreed that control methods mijr'.t be developed which woiild restore pjfclic confidence La shellfish as a food. The sale of shelifish in. Canada was £ericur»-ly affected cy the piblicity given to the occurrence of typhoid fever in the TJnited States. Since most of the oysters eaten in Canada were imported from yo'ur country some measure of protection was needed and regulationa were passed on July 3, 1925, under authority of the Fish Inspection Act which re- quired that "EgLCh consignment of oysters Imported into Canada, whether in the shell or in "bulk^ shall be accompanied Ir.y a certificate by a competent authority, that will be satisfactory to the Department of Health, that will show that the oysters contained therein are a safe food product". This was generally inter'preted to mean a license or certificate issusd by appropriate state agencies axA enda'sed by the Public Health Service of the United States Treasury Lepartjuent. This regulation is still La force. There does not appear to have been similar legislation invoied in the Lnited States at that time in respect to Ca:::sdia-'i shellfish but the States of Massachusetts atui Nev York;, which th-^n re_eived the bulk of our then very limited supply, were rightfixHy coxjcez'.;jsd with the control exercised over producing areas aiA pi-ocuctior. methols in Zioa&a.. Thus the Federal I>epart:mer.t of Health found it necesBar-y to concern it- self with these mattere atd bega:. to issue certificates to ejfpc3rters who were shipping to the iJnited States, From a consideration of the coi'T'espondence at that time it is evident that the Federal fe-alth Department of Jarada accepted the responsibility of issiing e:»:port certificates rather reluctaa^-ly and opposed, for a time, the. p::-oposai. that shellfish other than oysters should be considered. rhl£ reluctance is not sutprisirig sin.';e in- vestigations required eenning personnel from Ottawa to carry out field work, there being no field offices in the vicinity of the prodvicing areas. This phase of the control programme continued for' some ten years -2^40- at which time detailed Bsaitraz'y a'-.irweje of indivici.ual producing areas v'cvre started. O'ily Oljb p-ablic health er^glieer -wae araila^^ile for shell- fish control woLTi asd Oi)ly a part of hie ^zme- was assig::,.e'd to this »ork» In the meantime there had oeeii d.eveloped azL export trade in scallop meatj vhlch led to a demard, 'iij the States coz^-oeTned for regulatior: of the irdu£t.ry aad certlf icati.on by the Federal Department of Healtho A d.etailed stud.y was required, of production methods and equipment ori which -sras 'based legislatioji estaJolishing ml -r . m im. sani= tary reqali"'eiBgr.ts . Also during the' thirties boob interest was showa In the ejcport of soft=shell claias« The first appl3.cation for as. ea^iort certificate for shuefed clgms was received in 1938 » 'Hi'^ trend toward the export of shucked clam£ vas accelerated by Canadian legislation forbiddLag the e3cport of soft-shell clams in the shell from Kew Br'oaswiajfc in 19^5 aaii S'ora, Scotia in 19^6, Other i'sctors vh.i.eh had a definite effect on the export of shellfish fr-om Canad,& >-erc: (a) the outbreak of a disease among oysters in 1915 "Which spread to other ai'eas iii the twenties arid thirties and destroyed a high perceatage of the pop'jlationj, and ("b) the discovery of toxicity in clams ar.d mussels in the 3ay of IHindy area. The former reduced our control problem consideraJ-ile for a t,tme "but the same cannot "be said of the latter. Fatal poisonings j, "belieTed to hai"e 'been caused "by the coneumptio's. of mi.jF,str.'ls^ mere reported in lOYa Scotia in 1.936, Thisse Otcca.i'.'a^d ©r. tbi Bay of YaiAj shore and 1.5>i to action 'xsy the Prorvinciai gGTer^UE'Tct fbrDiddii-jg the imse of mussels in the general area. Fui'ther stud.ies "were th^s 'uad-ertaken for the piji'ptse of id.entifying all the area^ subject t© t0;«:icity asd. it was found that some of the most prod.uctive secti®as in the PrOYince of 'Kev Bruns'fc'ick, bordering the Bay of Fuadyj, veru also affected. Arrangements ve:.~e made with the lJepartme::it of fisheries aed the Fisher.ie6 .Resea;rch Board of Canada. for the reg'alsr eollee.tion of sanipleiG from vhieh extracts vere sent to the "La^oratciy ef Hygie^^c; of the Federal r-epartma::ri;. of Bes-lth for testing. Mice were Ja.»jwet4jd -with an acid=aqaeouB solution of the extract a:nd the degfee ©f toxicity dete.rmin£'d tj the time required to pi-o-iuce death. .As a. result of this st-jdy^ which is still "being purs'tijBd^ the daager seajson, the dangero-us a:rea.e a.nd the dargercas species of shellfish hare assevi identified. It might 'ae poi^xted. out that it required, sev'eral years of care^ ful in."re.'stiga.tion3 'before a thorough utjd.erEtscd.ing of this problem was ga±g.ed. D-Jj^-ing the ea:;''ly years of the study those e.^-porters holding certificates ccrrii;ring toxic areata had tliteii" certificates cancelled d.uring period.s when toxic conditions prevailed. This was too drastic since it preTented. those e.xporter?5 f:::'om taking clam.s from non= toxic areas o 'Ihe present proced.ure is to close the toxic as'eas 'by legis= lat.ion which is e-:iforefed Iby the riepar.i'.'tmfcint of Fishferies. Certificate holders are adidsed of the closures as they occur and also of the release of the areas when toxicity falls to permissiljle levels. '2i+l- It '*»-as later fouad that ooxieity was also a problem in the Province of QcieToec on toth the south and aorth shores of the £to Lawrencie River » This, ijiitil rece-.!2tly^ was a local problem since shellfish -were not e:)tported f^om the province of Que'^jee Uu.til early this year. A comjireheniiive programme of sampl:ing i-? now underway in Quebec and as a .-esolt toxic condltiOEjc. have "been foutid aloag the Gaspe Coast of ths,t iTOTince adjacent to the G;ilf of ,ot, Lavrence „ It should also "be noted that toxicity is -widespread or^ the Pacific Coast of fJanada and presents, in some respects ;, a mors difficult administrative problem since it persists throtighout the year and because it has not been possi'iile to dtserve an^" definite pattern in relation to the severity of the occurrence. This is contrary to o-ur experience in the ;cay of Fuady area vhere toxicities are usually low or nonexistent in most areas except in the summer and early autumn. Prior to 195^, the limits for toxicity in shellfish exported from Canada was less than 200 moa£,e units per 100 grami?- of meat^ this being the lowest detectable amount with the test Being losed,, This year^, 'by agreement with the Lnlted States authorities, the permissible limit was established as 400 mouse units per 100 grams of meat. Reverting now to the sanitary controls established on our Atlantic Coast reference has been made to detailed sanitary surveys of producing areas by a public health engineer. It s^as agreed that the P'ederal Department of Health would, be responsible for this phase of the control programme some tiir&nty years ago and this practice has since been followed. For sereral yea:;"s the sanitary suz'yey was carried out first and a decision was then made as to whether a bscteriol::gical inYestigation was needed. In recent years an effort has been made to have both studies made together bat this has pre- sented some difficultieiS because of limited laboratory facilities. In carrying out these investigations and in submitti-rig re- commendations for clos-izres because of pollution,, the Federal Depar-tment of Health acts in an advisory capacity to the Federal Depai'tment of P'isheries which has the legislative authority to control fisheries. The actual closures are mad.e by regiilations usier the Fisheries Act^ 1932. This act is basic to the control of the whole fisheries in- dustry in Gaaada since con.troI. of fisheries was assigi^ed to the Federal Government "dj the British 'Horth America Act under which Canada was founded. Authority to administer the Fisheries Act has since been delegated to some of the provioces but is administered by the Federal Lepar'tment of Fisheries in the Provinces of :S"ewfound.laad^ Prince, Edward Island^ Nova Scotia^ ar^d lew Brunswick which^ untli this year^ hare produced all the shellfish e>5)orte;^ certificate serves as an effective controlo It is very seldom that such dr-actic measijres muiit "be taken. Itl March;, 1950^ tentative limits of "bacterial contamination were es'tablistied ±1 relatici. to she^llfish inipcrted into Caradao Three classes were estafclishedy (l) a-cceptaZDle^ (2) accep^a■ble on coi.dition, and (3) rsjectable» Reports of ar.alyses are sent to ¥ashi-sgton<. In the "acceptable on coradition" category competent authorities examine pro= cessjjiig and hasc.l±ns methods to determine if possible the cause of the high hacteriai. contenx., While data is limited^ this arrangement seems to nave "been effective in securing a better quality product » This has "been an incomplete revie'j*' of Canad.ian snellf ish control Taut will perhaps serve to indicate that the shellfish industry is not a sinsple one to doai with from the point of view of the gove;i-nment offlcialo In fact thisra are proba'iily more administrative headaches associated therewith than with any other phase of our work and yet it has its fasclnatio".LS tooo Hew problems require consideration .BX'd additional kncr«,'ledge in many fields is essention ^i-efore maiclm'jnii use can "be made of o-iXiT' shellfish without eaiaitgering pabli.c healtho The presence of sjimdant shells tock in polluted areas ^ from the point of •"i'iew of the health department, is pro'bably the most sei'loue threat to adequate control asid is no doubt recognized as such "hj the industry itself. O^herefore some satisfactory meaixe must loe tosizA to purify and utilize polluted shellstoek la the interests of "both the Ind-jj^try^ the rv-igi;3.a-cory acthoritieSo a.nd the consiaiero It is a challenge t.o our research workers a:'^! should have the active support of the indiistry. ohould polluted shellfish "by intent or accident reach the con«i inner we may again experience a recurrence of disease similar in cha-rac'cer and reisiilts -co that of thirty y^ars ago. EVery effort must be made to prevent suc'h an occurrence. This description of our control programme ha^ eiirpha;=;ized the role of the Federal. Iiepar'cment of Health, lo should be noted, however, ttiat a close liaiaon exists with the Federal Department of Fisheries. Its officers enforce the clos"jres required hy pollution and toxicity- Without the wholehearted support of that department it would "be impossible to maintain an acceptable degree of compliance w.ith sanitary requirements. THE SMTTARY ASPECTS OF IMPORTATION 0? SHELLFISH liWO THE UIHTED STATES Richard 3. Green U. S. Department of »alth, Sducation, ard Welfare, Wa/shington, D. C« It ie a real privilege to report to this group orv the importation of shellfish from abroad. Tnis is one of the most complex shtllfieh sanitation proclem& facirife health and food control officials and the industry itself » I am especially pleased that Mr. Menzies of Canada coiild "be with us today. His excellent discussion of the development and operation of the agreement on shellfish sanitation hetveen the Canadian Department of National Health and Welfare and the Public Health Ser^/ice has presented a fine point of depart^jre for my talk. I feel rather sure, also, that some of the implications of recent developments will be of dir*ect in- terest and mutijal concern to him and his Canadian colleagues, and so it is fine to have this opportunity for us to exchange views. Some of you may remember that last year I h-ad an opportunity to outline for you in broad terms the impact of several recent technical and administrative developments on shellfish sanitation control in the United States. On that occasion, mention vas made cf the question of foreign shellfish imports, but neiuher tim.e nor the state of develop- ments then existing permitted more than a brief statement of this partic- \jlar problem. D\iring the past year, there have been many significant development", and a very considerable amoxont of time has been devoted to deliberations on this problem. We beliei'^e that it is especially im- portant for members of the Oyster Institute and related groups to be brought up-to-date. Since all of you .are familiar with the progi-am of shellfish sanitation control of the Public Health Service, it vrill be unnecessary for me to give you the details of our teclmique of cooperating with the States on the endorsement of State operatioris. You know ttjat the listing of certified dealers in our routine compilation, designed for use in consumer areas, is the backbone of this system of voluntary control. It was the acceptance of this concept of the certification system, and an understanding of the health department survei].lance involved in it, which brought about the reactions that followed the recent growth of shipments of shellfish from abroad. So many health officials in the United States require oystex-s and clams to be from certified dealers that shipments from foreign countries other than Canada have not easily been sold, even though admitted legally to the country under the terms of the Food, Dr-og, and Cosmetic Act administered by the Food and Drug Administration. That agency is responsible for permitting or denying entry to food imports. Faced with these difficulties, representatives of the foreign coiJixtries concerned and the United States importers have •2kG~ asked the Public Health Service ho-:ir their shellfish can ce accepted in a manner smilar to douestic a-id Cans.dian shellfish. At the same tiime, some Sta"ce and local health depar'cmeiLts have asked Vae Service what they sho-uld do abou^ foreign shellfish which ha-re appeared on the market - Thus, the Public Zealth Ser^-ice^ whj.,?h has no legal j'jrisdictiona tut which has guided the domestic cortrol program for manj' years, has "been caught in the ciiddle^ so zo speak, without being aJ)le to fur'nish answers that are satisfactory, Z do not have the final sasvers to these pioblems to give you todaj', "but I can. t,ell you what ire are facing and some of the reasoning we have usedo Since thijs program was developed, and still functiorxS, i" cooperation with the States and indus'cr;,'', the Public Health Service does not intend to proceed in the direction of major ad.justments without first discussing these matters with these groups. As indicated, above, responsibility for permitting or denying entry of such shipments when presented at ports of entry, under the terms of the Food, Dr-.'g, and Cosmetic Act, lies with the Food and Drug Administration, a sister agency of the Public Health Ser^yice in the Department of Health, Ediication^, and Vfelfare, Whenever the Food and Drug Administration finds, from the examination of samples or otherwise, that such shipments of shellfish have been produced londer unsanitary conditions, or are otherwise adiilterated or misbranded, their entry is refused admission» It is emphasized that refusal of admission to entry of food is based on evidence of aduJ-tsrationy or misbranding and that, in the absence of such evidence, entry must be permitted. Few will deny that, in the case of shellfish (oysters, clams, arxl mussels), a much greater degree of protection is afforded the con- sumer if sanitation controls can be based upon a sure knowledge of conditions surrq'anding the growir^^, harvesting, packing, and shipping of the shellfish, instead of on an objective examination of the final packages as received in the market. This principle of "control at source" has been the basis of the Public Health Ser-.-ice arid the State domestic shelLfish programs, as all of you who have seen State inspectors at work will attest. The effectiveness of this program may be judged by the low Incidence of shellfish borne enteric disease^ in spite of the fact that we have had to be concerned at all times over such problems as mailing sure tl-j£,t no shellfish are used f:rom the more than UOO areas on our coast line that are legally- closed because of polli.itiono Objective examination of samples colleetei from foreign shell- fish shipments at the tme of entry do not always give satisfactory evidence of sajiitary conditions under which the shellfish were produced and packed o It is, therefore ;, difficijlt to decide wliich shipments sho-^old be admitted and which denied, entry^, pai-tlcuJLarly when bacteriological findings do not clearly show the presence of significantly large numbers of coliform organisms, and when other objective findings are satisfactory, Before getting further into this disciission, I shoLild like to give you a few pertinent figures and some background information about *2t> the origin and size of foreign shellfish shipments vhich have arrived in the United States » ri-ior to World War II, few shipments of shell- fish came into the United States except from Canada ar^d Mexico. Mr. Menzies ' paper has already iiscussed the Canadian sit^^ition. In the case of Mexico ; most of the shipments were pismo clams, although an occasional shipment of shucked oysters was offered for entry. In 1952, somewhat over a half million poixnds of clam meats were imported from Mexico, principally thro^jgh the San Diego and Los Angeles ports of entry. In 1953, this figujre was close to three fourths of a million pounds. It is believed that almost all of these clams are used in production of heat pi"ocessed clam chowder; apparently, no attempt has been made to distribute the unprocessed clams beyond the State of entry, and thus the question of certification has not arisen. With the expansion of the frozen food industry since the end of World War II, several other foreign countries have developed an interest in the United States as a market for bivalve shellfish, principally frozen clams. Japan, Iceland, Australia, The Netherlands, France, Spain, China, and Panam.a have all exported or indicated an interest in exporting frozen clams, mussels, or oysters to us. It appears that the total volume of shellfish shipped to the United States has been relatively small, somewhere in the neighborhood of one or two per cent of our domestic production. It sho'uld be borne in mind, how- ever, that all these shellfish, except those produced in Canada, have been faced with the restrictions resulting from lack of certification. There is no easy way to predict what the ultimate vol^jme of shellfish imports might be if that situation did not exist. While it is beyond the scope of this paper, an.d entirely out of the field of piiblic health, to dwell on such facts as dollar exchange value, tariffs, and the importance to these foreign governments of trade with the United States, it woiild be a mistake to pass over these factors without mention. Specialists in such matters have analyzed the situation about as follows: International trade in frozen shellfish is now possible on a worldwide basis, and producers of shellfish in far distant countries are eager to help to satisfy what appeal's to be an jjicreasing demand for shellfish in the United States. The interest of foreign governments stems from the Importance of trade to their riational economies and the importance that a21 free world countries attach to closer ties with the United States. It is in our interest to foster such ties and to enable friendly countries to gain strength through trade. Their welfare and ours require that they be able to earn dollars from, their exports to the United States in order to buy the products of our farms and factories. Japan and Iceland, in particular, must sell us more goods than they now do to pay for all of the American products they need and want. Iceland has virtually nothing except marine products to sell abroad. In the case of Japan, marine products are among the few commodities which can be produced without the use of imported ravr materials. In the last few years, the governments of these two countries, -2k&. and of The Netherlands and Australia, alsO;, ha^re Eiade 'kmrdn to the Bepartaient of Sta'ce axid to the Paolic Health '6£irri:ie their i:-ioerest In working out some ar'rangemeats m'lich -would reinove unnecessary restrictions against the market in.g of ioiported shellfish irithout endangering the pulslic healxh- As i^nu may Imagine, "therefore, various officials of our' Departzttent of State hsTe dei.'elcped a great interest in this prcblea., and -^re are being urged to expand our pre- s,e:zt system of certification to these and other foreign countries. The Public Health Service does not '>rant its cooperative system of shel2.fish sanitation contrrjl within the uni'ced Sta":es to act as an artificial trade barrier against legitimate shellfish shipments ■K'tdch have been prodi,:ced and pac>.ed binder conditions eq-oal to those required of cur o'^n packers <, On the other b^.nd, even if the Piiblic Health Service had tlie authority to do so—- which it does not there would be very great difficiilties involved in extending this certification system to otner countries. F-oll knowledge of these difficulties is necessary if these most interested are to face the problem intelligentlj^^ The application of our system of Public Health Service endorse- ment of over=all State progr-ams presumes that representatives of the Service keep in fairly close touch with control efforts of the indi- vidual producing States by reasonably frequent consultations with State personnel^ cooperative investigations, and check inspections. We believe that we cannot report suiequately to the country as a whole Qijr cpini-ons on the effectiveness of the local procedures unless we maintain this tj'pe of contact. This reasoning has been applied even in connection with our agi-eemeut with Can-ada, which specifically in- cludes provision for the excba:age of information on methods of pro- duction and handling of shellfish and for Inspection visits across the border « ?rom a practical point of view, it has been very easj'' for the Public Health Servi.ce to meet the provisions of o-'or agr^eement with Canada covering the interchange of infomiation on shellfish sanitation. The capitals of the ti^o countries are only a few hours apart by air, snl long distance telephone conversations ai'e relatively inexpensive. Also, it has cost only a small sum each year for us to keep in close touch with operations in the Canadian Ifer'itjjae Provinces, and in British Columbia on Canada's west coast, by extenclir^g routijie field trips to these areas while oxxr men are vrorking in Maine and. the State of Washing- ton. Health officials in the two countries have mimy other mutual in- terests, and official contacts are frequently made on matters other than shellfish sanitation. There is, therefore, a cor^stant inter- change of information made possible at relatively low cost. In addition, all of our cooperative efforts with Canada have been built on a long history of parallel development in the two countries, both as to tech- nical procedures aaa administrative operations. It is easy to see that none of the£?e favorable elvements CQ-old be duplicated if the concept of • certified dealers and "endorsed" control programs were to be extended to other foreign countries. -2l+9- There are no provisions in the Food, Drug, and Cosmetic Act, under which the Food and Erug Administration operates, which would make possible an:/ routine international exchange of information about techniques of" sanitation control at source, miAch less prevision for setting up any plan of international certification or endorsement of any foreign operating control program^ In the view of officials of t;he Food and Drug Administration, the onl^' justification ■i,a:ider the Food, Drug, and Cosmetic Act for that Admirilstration to use its appropriated funds to send a representative to a foreign coimtry would be to gain infoi-ma'cion considered necessary for the proper enforcement of the Act in connection with foode or drags offered for entry into the United States.. I understand that sucn visits have been rare for various reasons. In the first place, a single trip to a foreign, country for inspection purposes can only develop information of limited usefulness » In order to carry out the type of inspections performed in this country under authority of the Federal Food, Driag, and Cosmetic Act, it is some- times necessary to visit one or more plants several times during the year. The obvious limitations of funds and personnel make such trips to foreign countries generally unproductive, as compared to the expendi- ture of comparable time and money in inspections in this cotmtry. An occasion may arise where a single trip or visit to a foreign country may supply basic infonnation necessary to evaluate fully a particular situation^ During January and February of this year, a team was sent, at the invitation and expense of the Goverimient of Japan, to inspect the shellfish industry of that coiantryo The writer was assigned as a sanitary engineer consultant to the Food and Drug Administration for this trip, and, in the company of Mr. L. R. Shelton, a bacteriologist of the Food and Drug Administration, gathered a large amount of in- formation which will be helpful in futiire considerations of problems involving Japanese shellfish. Aside from the complicated administrative problems outlined previously there are certain other factors which ai*e important in any consideration of this over-all problem: lo We have already considered the limitations of the objective examination of shellfish at the time of arrival of shipments in this coiontry. If strongly positive bacteriological results are obtained, one may assume that the shellfish were prodiiced or handled imder insanitary conditions. However, when bacteriological, results are negative, interpretation becomes much more difficult. 2. In spite of a great deal of research, we believe that there has not been established for o-jt own species of shellfish any firm relationship between bacterial content of shucked shellfish in the ■250- market and the quality of growing areas and. cond.ition.B of handling. This is vhy ve have not found it possTole to adopt a final "bacteriological standard for market quality,, As you know, TTOrk vhich h&s ceen done so far in this field has dealt chiefly with fresh shuekel o^'S':er& and clans, a:id has not considei'ed x'rosen products.. Undo'Jitedly, the freez- ing and prolonged storage of shellfish produced atroad will have some effect on its apparent 'bacterial cantsnt, to complicate the picture further' » 3o In the United State-s and Cansdii, certa,in species of shell- fish, notably clams and lausssls^t a.re sometimes subject to the accum'jla- tion of organic toxins during part of the year,. The origin and action of these toxins are fa:i:."ly -vfeil Lir.derstood , and a eomglex administra- tive control program is in operation to prevent toxic shellfish from "being used commerclallyo Adequate test procedinres are availa"ble and are "being improved o However ^ there is pome rea.Eon to believe that toxin -which sometimes affects certain species of foreign shellfish may not be so well understood^, and it is not certain that adeqiiate tests liave "been developed » k. Most of the frozen shellfish which woiild be shipped to the United States would be cooked before use. In fact, one Importer has been investigating the feasibility of introducing clams which would "be given some cooking before being frozen for shipment, this product being intended for use as chowder stock. It is milikely tliat many frozen shellfish fron abro,ad would be consumed rawo Tills factor is mentioned, not because we feel that there snoiold "be auy significantly different standards applied to shellfish intended to be heat processed before sale, but simply because the facts of the matter seem to indicate that any health hazard wliich might be present in connection with bacter- ial contamination of frozen shellfish from abroad wo\ild be considerably reduced by the cooking process » "s^e do not "believe that this expected heat treatment shovld be considered in ai\y way as a cover-up for a filthy item, 0:^16^^ as j^ou Icnow, this attitude is basic to the thinking of the Food and Drug Administration, also., ¥e join with those wno are concerned that there are in operation t>70 parallel mechanisms of sanit^sry control th-ro-ogh which imported shellfish on the one "hand may be admitted to the coimtry, and on the other hand, thejjr sales maj be discoiiraged. Foreign governments quite nat\r.'ally find this situation extremely difficult uo ijnd..&rstando The reason, of course;; is that ohere are two different sources of legal authority, one Federal and one State « VJe hope to develop a workable approach to tlie problem in time for it to be given full corisideration at the forthcoming National Con- ference on Shellfish San.itation, scheduled to be held in Washington on September 9"^^ and lOtn, This Cord'erence, which is being called by the Si'irgecn General of the Public Health Service at the request of the -2:^1- Conference of State and Territorial Health Officers, vill review all aspects of shellfish sanitation control in the United. States « Since this will 'be the first over-all reevaluation of our program "by the States and the industry in almost 30 years, we look upon it as a significant event. The committee which is developing a detailed agenda and proposed procedures for the Conference includes Mr. Wallace, of your Association. You may be sure that the question of foreign shellfish will be given a prominent place in these forthcoming de- liberations. We urge your interest and participation in this Con- ference, becaiise we are sure that the decisions made at that time will have a major bearing on future activities of the Pibllc Health Service in the field of shellfish sanitation. -252- THE DEVELOPMENT OF RECOMMEKDEB PRACTICES FOR SMITARY COIWROL OF THE BEEADIWG AND FREEZING OF SHELIFISH (l) Eugene Tc Jensen U. S. Department of Health, Education, and Welfare;. Washington, D.C. Freezing is not a new me'chod of preserving foods,. Actually, this process has "been \ised in cold climates since prehistoric times for preservation of perishable foods, particularly fish and meats. Appli- cation of freezing to commercial preservation of foods is, however, a relatively recent development » To a New Englander, Enoch Piper, of Camden, Maine, goes the credit for the first commercial process for artificial freezing of fish. Almost a hundred years ago, this "down Easter" developed a method in which a salt- ice mixture was used as a refrigerant (2). But a completely feasible, commercial freezing process was not develop- ed until the 1920 's, when reliable, mechanical refrigeration equipment "became generally available <. Since the end of World War II, the frozen food industry, paced hy a high degree of public acceptance of its pro- duct, has grown rapidlyo Today, frozen foods are sold "by almost all grocery stores; many homes have small freezers; and almost all ho\ise- hold refrigerators have frozen food storage space. There is no doubt that frozen foods have "been well accepted by the consuming public. With some foods, this degree of acceptance has been so complete that sales of canned and fresh products have been adversely affected. Most of you are aware of the tremendous expansion of the frozen, concentrated citrus juice industry (3)- Whether freezing will have an equivalent effect on the shellfish in- dustry is problematical; only time will supply the answer. In theory at least, freezing is an almost perfect means of marketing a highly perishable product, such as oysters. Most of you, I believe, have had some experience with the process. These exper- iences, probably, have not been uniformly successfiil. Frozen oysters, at times, tend to brown, or may pick up a rancid flavor. Consumers have not yet been educated to the fact that oysters are a good summer food; many people still believe the old "R-month" myth. Various types of containers have been tried, freezing processes have been altered, and new packing methods have been adopted. It seems almost inevitable that, eventually, a method will be developed resulting in a frozen pack which will be as completely successful, from a quality standpoint, as is the fresh, shucked pack. Within the last three or four years, there h&s been a trend in the industry toward development of a ready-to-cook product, and even an alread.y- cooked product. This trend is simply a phase of the more general -253- drift toward production of prepared or partially prepared foods which has affected the entire food processing industry. Most of you are familiar with ■:he joint State-Federal-Industry certifica'cion system which has beer, u^ed foi- mary years, and you know that the certification syszem is applicable to the production and marketing of frozen shellfish (k) . Frozen shellfish which have been processed and identified under this sytem, move without difficulty in interstate commerce, as long as the dealer maintains his certificate number , With the advent oi' the breaded, frozen product--- as contrasted with the dimply frozen product--- a new problem arose » Since the breaded product invariably would be cooked before it would be eaten, there was a problem of determining whether it sho\ild be included \inder the certification program or considered exempt from the certification system as a processed food. In 19?1> we discussed this question with officials of the Food and Drug Administration, vrith Mr. Wallace, of the Oyster Institute, with some of the interested members of the industry, and with State officials responsible for shellfish sanitation programs. After care- ful consideration, it was decided that the certification program should be considered applicable to the breaded and prefried products, even though it was certain that all of such products would be cooked before being eaten, I believe it is important that you know the basis for the decision. There were two principal considerations: 1,. The basic component of this prepared food is shellfish- - usually oysters, elthough we understand that some breaded clams have been marketed. Brsaded foods ajre not sterilized du?."ing the frying process because of the insulating effect of tte breading material » Thus, if the shel.lfish should come from a contaminated source, some disease -causing bacteria might sui'vive the cooking process. In addition, the sometime? toxic properties of clams ai'e a consideration that we believe must be given cor,E iderable weight. 2=. The existence of a market for large quantities of non- certified shellfish would greatly complicate the job of the State eriforcement agencies » This is particularly true if you coiisider that breading plants might be — ■- and, in fact, are--- located in the interior States, away from the organized shellfish control activities of the coastal States. In addition, there was a strong feeling that it would be con- fusing to many persons, both in the industry and in the erJforcement -25I+- agencies, to apply the certification system to one part of a plant and not to another pai't of the plants Similarly, there v&.s a strong belief that receiving States and cities, eventually, would question the sani- tary quality of frozen, breaded oysters which did not show evidence of having been processed in a State certified establishment o Recent ex- perience has demonstrated that such corxfuslon and marketing difficulties will develop unless the product carries a certification number. The administrative decision to include breaded and/or prefried frozen shellfish in the certification program raised the problem of appropriate sanitary standards <. In general, breading is a clean operation; however, the use of the breading material results in some sanitation problems very different from those associated with the shucking-packing operation. In certain respects, the breading plant has the sanitation problems of the ordinary shellfish packing plant and, in other respects, the sanitation problems of a baker, as well. We had no ready krxswledge on which to formulate a set of standards, so a process of fitting standards to the industry as it existed was undertaken. Experienced shellfish sanitarians from the Public Health Service, working in cooperation with the State shell- fish control agencies, visited plants which were breading shellfish, and made a careful study of the various steps in the operation. This study of the breading process made it possible to pinpoint those steps which would require the most carefxil control. Almost a year was spent in making an evaluation of these operations- Our very real appreciation goes to the plant operators who assisted us in making these baseline studies o Using the information which had been obtained by observation and study, a tentative set of "Recommended Practices" was developed. This tentative manual, 32 typewritten pages, was sent to the Public Health Service field offices for review by their food technologists. Many comments and suggested cl'ianges were made. The next developmental step consisted of a review of the manual by other official agencies, and by members of the shellfish industry who were Interested in the breading process. To accomplish this, over 200 copies of the "Recommended Practices" were sent to all State health departments, the Food and Drug Administration, the Fish and Wildlife Service, the Oyster Institute, the Pacific Coast Oyster Growers Associa- tion, and the National Fisheries Institute. The response to this request for assistance was most gratifyingo In fact, severaJ. hundred pages of comments were received! Working these comments into a ^0 page manueul was a chore that required several months and some lengthy conferences with interested parties. As a result of this review process, we believe that the recently released "Manual of Recommended Practice for Sanitar-y Control of the Breading and Freezing of Shellfish" should be a relatively good guide ■255' for maintaining sanitary conditions in shellfish breading estalilishments. However, we have decided that we •will take no action toward final adoption of these "Reconmiended Practices" until we have had at least one year's operating experience -with them in vaxio'JS parts of the country. The Manual, together with its accompanying rating form, has already iDeen used for the eval-Xiation of oyster breading plants in Virginia. It seems rerj likely tmt some changes will he made in the "Recommended Practices" as a result of field use; however, we believe that the changes will not be of a fundamental nature, but will relate instead to the smaller operational details. Those of you who operate and manage shellfish breading plants could be of great assistance to vs by becoming thoroughly familiar with the manual as it would apply to youi- plant o Any errors or dis- crepancies should be called to our- attention^ If you do not have a copy of these "Recommended Practices", and if you are interested in this phase of shellfish packing, you can get a copy from Mr. David Wallace of the Oyster Institute, or you can write directly to the Shellfish Branch of the Milk, Food and Shellfish Sanitation Program, Public Health Service, Washington 25 ^ D. C. The following simmary will give you some idea of the principal sanitation requirements of the new manual: Plant Construction and Arrangement : Plants should be con- structed so as to be easily cleaned, and so as to furnish minimum harborage for insects or rodents. In general, this will mean about the same type of construction as has been used in packing rooms. The "Recommended Practices" will require a separate breading room, but will permit its use for other purposes, provided that such operations do not interfere with the breading operation. Adequate screening and lighting are, of co-'orse, required. No special heating or ventilating equipment is required, except for special ventilation systems where breading machines are operated. Water Supply : A safe water supply is a fundamentaJ. sanitation requirement of any food processing plant. In addition, it will be required that water be piped to all food processing rooms, and that an adequate hot water heating system be provided. Plimibing ; The safety of a water supply is intimately related to the quality of the plumbing, and to the skill with which the plumbing is installed. Plumbing which complies with your State plumbing code or with the National Plumbing Code is, therefore, a requirement of the "Recommended Practices." -256- Toilet facilities es'e an Itoportant part of the pl-umoing in a, breading plant. The requl;"'emeii^s-==3Ciae«rh.a'' a'i,OYe: those of the old shellfish inanual---are those reeoumended by the Natio33al Plumbing Code« Hoveverp ve believe that mcder'^ sanitation, particularly fly control, has removed the need for the intervening vestibule, and this requirement has been deleted. Disease outbreaiis have been caused by leakage of sewage from defective overhead sewers « The "Recommended Practices," there- fore require that there be no overhead severs in food processing areas. Handvashing is perhaps the most import-anx. single sanitation item in a food processing planto To make it easy for workers to wash their hands, an adequate number of handwashing sinks, complete with hot and cold water,, soap, and sanitary towels, is a must. Re- search workers have, in the past few yes-rs, developed several types of soaps which contain an added bactericide » These special types of soaps are much more effective for killing bacteria than are ordinary soaps, and their use has, thus, been required. Presumably, the use of bactericide containing soaps will eventually be required in shucking- packlng plants. Rodent Control ; Control of rodents in oyster shucking houses has never posed any real problem. It seems likely, however, that rodent control problems will exist in breading plants. It has been required, therefore, that buildings be of ratproof construction, and that rodenticides be properly handled and stored. Equipment Construction : As in previous manueu-S there are no specific requirements for equipment construction. Equipment should be constructed of material which will not readily corrode, which is easily cleanable, sjid wh.ich is nontoxic. To make cleaning easy, all joints sho^jld be smoot"nl.y welded or soldered; corners should be filleted; and there should be no rough or inaccessible areas. The milk industry, in cooperation with the sanitation auxhoritles, has developed specific construction standards for much of the equipment which they use. Thus, the operator of a pasteurising plant can buy- equipment which meets the ''3=A" Standards with --sss'orance that he is getting equipment which will comply with all sanitation requirements. Perhaps the shellfish industry might profit by this ei?perlence by- developing its own standards for equipment used in shellfish processing. Certain cons true tio'L. items for breading machines ha-/e been specified because of the rjature of the breading operatio-n. For example, it has been required that breading machines be easily cleaned, so that they will not harbor insects or rodents. Proper design and construction of the machine can save the plant operator many houurs of cleanup work. Refrigeration of the perishalle batter has been required, although we know that not all ma,chin.es now on the market provide such refrigeration. -257- Plant Personnel and SuperyiiBlon; Most of you are familial' with the requirements for supervisors in i3iiucking=packing pla:atSo We have fourd that some person actually li. the pla;<-jt==<=:u.ot the maiiager In the front offlce===mu;3t 'be responsiZole for seeing that employees wash their hands and -wegtr eleaa clothes <, If supervision is lax, plant workers will teni to pay less and leiss attentioi.. to these important sanitation measijres^ Source eg^ Co:r3di tioz of Shellfish ; The "Kecommended Practices" require that all shelliish come from a certified or otherwise approved source. Shucked shellfish miist be shipped in approved sealed containers, and mu£,t have a tvemperatu:''e of i-O^c or less c^ arrival at the hreading plant o Bread i:ng of f.ro^en oys'.ters has loeen prohicitedo Breading Mjdrgrlal; The material used in Toreading— -the batter mix and the "breading material— --should "be p-ui'chased in containers which will afford a maxim-urn degree of protection to the product. After arrival at the plant, the Datter mix and breading materials shoiild be stored so as to be protected from contamination. Breading Operations ; In general, the mechanics of preparing the breaded shellfish have been left to the discretion of the plant o-peratoTs although certain limiting guidelines have been established. For example, the perishable batter should be refrigerated} grinding and repose of lumpy breading materials is prohibitedi and reuse of breading materials left over at the exid of the day's operation is prohibited. Storage of Containers ; There is no convenient way to sterilize paper containers'~at the breading plant before they are filled. Hence, it is necessary that packagi-Xtg m8ter:ials be clean when purchased, and that they be kept clean by storing them where they will not be subject to contamination. Usually, a special storage area wi.ll be needed. Cleaning and Sterilizing of E ^uigngnt ; The requirements for cleaning and sterilizing of equipment are the same as those now in use in the shucking=packlng plants, except that some special problems in sanitizing are pcsed by the breading process. Adequate cleanup facilities, including a wash sink, detergents, arid brushes, are required. Prefriel Sh ellfish ; A few operators have been interested in the preparation of breaded prefried shellfish. The sanitation problems involved in the preparation of this product are esssntially the same as those in the ordinary breading establishment, except that the presence of grea,se from the frying process may complicate cleanup work. Adequate ventilation equipment is the key to the problem, and m^jst be provided where deep fat frying is practiced. • Packaging and Labeling; Tne Food, Drug, and Cosmetic Act re- quires that certain information be shown on each package of food. This -258.. information includes: a. The name and address of the packer or distriDiitoro b. The common or us"-ial name of the food, c. The common or usual name of each ingredient used in its production, except that spices or flavorings may be declaired as sucho do An accurate declai'ation of net weight. To insure that the product will te acceptable in all markets, the packer should a^so indicate his certificate number jxreceded by the abbreviated name of the State, We have had several complaints about noncertified products which were eventually traced to the type size of the certificate number <, In some instances, these numbers have been so small that they were virtually impossible to find. Hence, the "Recommended Practices" specifies that these numbers be prominently displayed, and that they be at least 3/l6 of an inch high. Also, packages should be conspicuoiisly labeled "PERISHABLE-- KEEP FROZEN," The code or date of packing should be placed on each carton, but need not be visible to the ultimate consumer. I should point out that code dating of master cartons does not satisfy this requirement. Freezing of Breaded Shellfish : To avoid excessive growth of bacteria, the breaded shellfish should be frozen as soon as feasible, preferably within a few minutes after packaging. Recording thermom- eters are required for the freeze room. This resume of the shellfish Breading Majiual touches on only the most salient points, I must remind you that the requirements contained in the "Recommended Practices" are not yet final, and will doubtless be siibject to some readjustment during the coming year. Those of you who are active in this field can be of real help by calling any errors or discrepancies to our attention, so that they may be corrected. If you disagree with any of the provisions of the manual, I suggest that you contact us so that we may discuss these problems with you. With yo-ur assistance^, we should be able to develop a manual which will insure a sanitary product of good quality without imposing excessive demands on the industry. ■259- Literature Cited (1) Manual of recommended practice for sanitary control of the breading and freezing of shellfish. Divo Sanitary Engineering Serv., Public Health Serv., U. So Dept. Health, Educ. & Welfare. (2) Tressler, D. K., and C. F. Evers. 19^?. The freezing preserva- tion of foods. Avi Publo COo, Inc., N. Y. (3) Frozen foods, a $700 million business last year. Chem. & Engineer- ing Wews 29(11), March 12, 1951. (k) Manual of recommended practice for sanitary control of the shell- fish industry. Public Health Serv. Publ. No. 33, Public Health Serv., U. S. Dept. Health, Educ.^ & Welfare. (5) Report of the Coordinating Committee for the National Plumbing Code, U. S. Dept. Commerce, 1951' -260- Papers Presented at the Convention but Publiphed Elsewhere : Moulton, J. M., and G. W. Coffin. 195^. The distribution of Venus larvae in Orr's Cove plankton over the tide cycle and during the summer and early fell of 1953. Res. Bull. 17, Dept. Sea & Shore Fish. , Me . -261- DIRECTORY OF MEMBERS OF THE NATIONAL SHELLFISHERIES ASSOCIATION (To April, 1955) Aldrich, Dr. Frederick A., Assistant Curator of Limnology, Academy of Natural Sciences, 19th. and the Parkway, Philadelphia 2, Pa. Allen, Dr. J. Francis, Department of Zoology, University of Maryland, College Park, Md. Andrews, Dr. Jay D., Oyster Biologist, Virginia Fisheries Laboratory, Gloucester Point, Va. Atlsjitlc Biological Station, Fisheries Research Board of Canada, St. Andrews, N. B., Canada. Baker, Byron B., Jr., 7222 Marywood Street, Landover Hills, Md. Ball, Eric T., 212 Simmiit Street, New Haven I3, Conn. Baptist, John P., U. S. Fish and Wildlife Service Shellfish Laboratory, Beaufort, N. C. Beaven, G. Francis, Maryland Department of Research and Education, Solomons, Md. Berry, W. R., Department of Health, 301 Essex Building, Bank and Plume Streets, Norfolk 19, Va. Bloiint, F. Nelson, Blount Seafood Corporation, 383-393 Water Street, Warren, R. I. rButler, Dr. Philip A., Chief, Gulf Oyster Investigations, U. S. Fish and Wildlife Service Shellfish Laboratory, P. 0. Box 1826, Pensacola, Fla. Carriker, Dr. Melbourne R., Department of Zoology, University of North Carolina, Chapel Hill, N. C. Chanley, Paul E., U. S. Fish and Wildlife Service Biological Laboratory, Milford, Conn. Chestnut, Dr. A.. F., Institute of Fisheries Research of the University of North Carolina, Morehead City, N. C. Chipman, Dr. Walter, Director, U. S. Fish and Wildlife Service Shellfish Laboratory, Beaufort, N. C. ■-262, Collier, Dr. Albert, Cnief, Gulf Fishery Investigatior^j, U. S- Fish and Wildlife SerTice„ Fort Cr*fekett, Galvestcrt;, Tex. CroniE.;, Dr. Eugene, Director, Maryland Department of Reeearch and Education, Solomons, Md. Currier, Wendell, Assistant to the Tice-President, Research and Develop- ment,, CanrplDell Soup Co., Camden, IT. Jo Darling, J. S. & Son, P. 0. Box 4l2, Hampton, Va. Davis, Harry C, U. S. Fish and Wildlrfe Service Biological Laboratory, Milford, Conn. Dawson, C. E., Institute of Marine Research, Port Aransas, Tex. Deiler, Frederick G., Biologist, Freeport Sulphur Co., Port Sulphur, La. Dow, Robert L., Director of Marine Research, Department of Sea and Shore Fisheries, Vickery-Hill Building, Augusta, Maine. Dumont, William H,, U. S. Fish and Wildlife Service, Washington 25, D.C. Dunnington, Elgin W., Department of Research and Education, Solomons, Md. Ellison, William A. , Director, Institute of Fisheries Research of the University of North Carolina, Morehead City, N. C. Engle, James B., Chief, Chesapeake Shellfish Investigations, U. S. Fish and Wildlife Service, P. 0. Box 151, .Annapolis, Md. Fahy, Dro William, Institute of Fisheries Research of the University of North Carolina, Morehead City, N. C. Flower, Frank M. & Sons, Growers of Pine Island Oysters, Bayville, Long Island, N. Y. Fox, Leo, Department of Public Health, 511 A State House, Boston 33^ I4ass. Galtsoff, Dr. Paul S., Director, U. S. Fish and Wildlife Service Shellfish Laboratory, Woods Hole, Mass. Ganaros, Anthony E., U. S. Fish and Wildlife Service Biological Laboratory, Milford, Conn. Gibbs, Harold N., A- 71 Scrwams Road, Barrington, R, I. Glancy, Joseph B,, Shellfish, Inc., Box 212, West Sayville, Long Island, N. Y. -263- Glude, John B., Chief ^ Clam Investigations, U. So Fish and Wildlife Service, BootHbay Harbor, Me. Green, Richard S., Chief, Shellfish Sscdtation Branch, Public Health Service, Room ^113, DHEW Building, South 3rd. and C Streets, S. ¥., Washington 25, D- C. Greenwich Oyster Company, Greenwich;, K. J. Grice, Dr. George D., Oceanographic Institute, Florida State Univ- ersity, Tallahassee, Fla. Gunter, Dr. Gordon, Acting Director, Institute of Marine Science, Port Aransas, Tex. Gustafson, Dr. Al, Chairman, Department of Biology, Bowdoin College, Brunswick, Me. Hammer, Ralph, Maryland Department of Tidewater Fisheries, State Office Building, Aimapolis, Md. Hanks, James E., U. S. Fish and Wildlife Service Biological Lab- oratory, Milford, Conn. Harrison, George T., President, The Tilghman Packing Co., Tilghman, Md. Haskin, Dr. Harold H., Director, Oyster Research Laboratory, Bivalve, N. Jo, and Department of Zoology, Rutgers University, New Brunswick, W. J. Haven, Dexter, Virginia Fisheries Laboratory, Gloucester Point, Va. Hayes, E. C, Jr., Assistant Director, Department of Agriculture and Conservation, Veterans Memorial Building, 83 Park Street, Providence 2, R. I. Hedrick Brothers Oyster Company, 730 Auster City Street, New Orleans, La. Hewatt, Dro Willis G., Biology-Geology Department, Texas Christian University, Fort Worth, Tex. Heydecker, Wayne D,, Atlantic States Marine Fisheries Commission, 22 West First Street, Mount Vernon, N. Y. Hofstetter, Robert P., Bay Oaks Addition, La Porte, Tex. Hopkins, Dr. Sewell H., Biology Research Laboratory, Texas A. & M. Research Foundation, College Station, Tex. '26h^ Euber;, L. Albertson, Hydrograpliic Engineer, 297 E. Commerce Street, Bridgeton, N» J. Jensen, Eugene T,, Shellfish Branchy, U. S. P"jblic Health Service, Washington 25, D- C. Kahan, Archie M. , Executive Director, Texas A. & Mo Research Foundation, College Station, Tex, Lamson, P. G., PulDlisher of "Atlantic Fisherman", Goffstown, W. H. Lednum, J. M., Town Engineer, Town of Islip, 1. Y- Lester & Toner, Inc., j> Royal Toner, Fulton Market, New York 38, K. Y. Lindsay, Cedric, Shellfish La3Doratory, Fisheries Department, Washington State, Quilcene, Wash. Littleford, Dr„ Rohert A, , Department of Zoology, University of Mary- land, College Park, Md. Logie, Ro R., Department of Zoology, Rutgers University, New Brunswick, N. J. Loosanoff, Dr. Victor L., Director, U. S. Fish and Wildlife Service Biological Laboratory, Milford, Conn. Lunz, G. Robert, Director, Bears Bluff Laboratories, Wadmalaw Island, S.C. Mackin, Dr. J. G», Director, Marine Laboratory, University of Teicas Medical Branch, Galveston, Tex. Macomber, Ronald, U, S. Public Health Service, 11 Prescott Avenue, Montclair, N. J. Manning, Joseph H., Chesapeake Biological Laboratory, Solomons, Md. Mansueti, Romeo, Maryland Department of Research and Education, Solomons, Md. Mstrshall, Dr. Nelson, Saunders Point, Niantic, Conn. McConnell, James L., Department of Wildlife and Fisheries, New Orleans, La. McConnell, James N., Director, Division of Oysters and Water Bottoms, Department of Wildlife and Fisheries, New Orleans, La. McHugh, Dr, L. H., Director, Vrrginia Fisheries Laboratory, Gloucester Point, Va. .265- Menzel, Dr^ R« Winston, Oceanographic institute, Florida State Uni- versity, Talls.hassee, Fla. Messer, Richsur'd, Director, Division of Engineering, Department of Health, 713 State Office Building, Richmond 19, 7a.. Miles, J, H, 8c Co., InCo, Norfolk 1, Va. Nelson, J. Richards, President, The F, Mansfield & Sons Co., 6IO Quinnipiac Avenae, lew Haven, Comio Nelson, Dr. Thurlow C, Department of Zoology, Rutgers University, Nev Brunswick, N. J. New Jersey Department of Conseirvation, Trenton, N. J. Perlmutter, Dr. Alfred, Bureau of Marine Fisheries, Conservation Department, State of New York, 65 West Sunrise Highway, Freeport, N. Y. Pomeroy, Dr. lawrence. Marine Biology Laboratory of the University of Georgia, Sapelo Island, Ga. Pritchard, Dr. Donald W., Director, Chespeake Bay Institute of the Johns Hopkins University, Box U26A, R.F.D. #2, Annapolis, Md. Ray, Dr. Sammy M. , Biology Department, Rice Institute, Houston, Tex. Rego, John L., Director, Department of Agriculture and Conservation, Veterans Memorial Building, 83 Park Street, Providence 2, R. I. Rice, Dr. Theodore R., U. S. Fish and Wildlife Service Shellfish Laboratory, BeaixTort, N. C. Ropes, John W,, U. S. Fish and Wildlife Service, 29 Linden Street, Salem, Mass. Russell, Henry D., Springdale Avenue, Dover, Mass. Sangree, Dr. John B., Glassooro State Teachers College, Glassboro, N. J. Sieling, Fred W., Department of ResesLrch and Education, Snow Hill, Md, Smith, Dr. F. G. Walton, Director, The University of Miami Marine Laboratory, Coral Gables k6, Fla. Smith, Osgood R., U. S. Fish and Wildlife Service, 13 State Street, Newburyport, Mass. -266- Sollers, Allon A. ^ 1305 Park Avenue;, Baltimore 17, Ma. Sprague, Victor^ Hiawassee, Ga. Truitt, Dr. Reginald Vo^ Maryland. Department of Research and Education, Solomons, Md. Udell, Iiarold_, Bureau of Marine Fisheries, New York Conser^/ation Department, Freeport, Long Island, No Y. Virginia CommisGion of Fisheries, Newport News^ Va. Wallace, Dana Zo, Shellfish Specialist, Department cf Sea and Shore Fisheries, Vickery-Hill Building, Augusta, Me. Wallace, David H., Director, Oyster Institute of North America, and Executive Secretary of the Oyster Growers and Dealers Associa- tion, 6 Mayo Avenue, Bay Ridge, Annapolis, Md. Webster, John R., U. S. Fish and Wildlife Service, ?. 0. Box 151, Annapolis, Md. Weiss, Dr. Charles M., Sanitary Chemistry Branch, Medical Laboratories, Army Chemical Center, Md, Vfclch, Wailter R., Clam Investigations, U. S. Fish and Wildlife Service, Boothbay Harbor, Me. Westley, Ronald E,, Shellfish Laboratory, Fisheries Department, Washington State, Quilcene, Wash. Whs.ley, Horace A., Chesapeake Bay Institute of the Johns Hopkins University, Van Buren Street, Annapolis, Md. WoLaan, Abel, Johns Hopkins University, Whitehead Hall, Baltimore l8, Md. Wright, Thomas J., Chief, Division of Fish and Game, Veterans Memorial Building, 83 Park Street, Providence 2, R. I. Wurtz, Charles B., 32^7 Disston Street, Philadelphia k9, Pa. -267- ^S^i^O MBL WHOl I lltHARY iiiiiiiiiiiiiiyiiiiiii UH lACL 7