W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 1990 The Gametogenic Cycle of Placopecten magellanicus (Gmelin) in the Mid-Atlantic Bight Anne Catherine Schmitzer College of William and Mary - Virginia Institute of Marine Science Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Marine Biology Commons, and the Oceanography Commons Recommended Citation Schmitzer, Anne Catherine, "The Gametogenic Cycle of Placopecten magellanicus (Gmelin) in the Mid- Atlantic Bight" (1990). Dissertations, Theses, and Masters Projects. Paper 1539617621. https://dx.doi.org/doi:10.25773/v5-b6en-ra23 This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. THE GAMETOGENIC CYCLE OF PLACOPECTEN MAGELLANICUS (GMELIN) IN THE MID-ATLANTIC BIGHT A THESIS Presented to The Faculty of the School of Marine Science The College of William and Mary in Virginia In Partial Fulfillment Of the Requirements for the Degree of Master of Arts by Anne Catherine Schmitzer APPROVAL SHEET This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Arts Anne C. Schmitzer, M. 8*4 Approved, January 1990 d&tCsi William D. Committee Chairman 4~ {-UsU ^ /James E. Kirkley, d. (?) ~72x>*>— Bruce J.yifarber, Ph.d. g I*. 73 r^i Eugeni M. Burreson, Ph.d. /I i Evon Ruzecki, 4Ph.d. TABLE OF CONTENTS Page ACKNOWLEDGMENTS ...................................... iv LIST OF TABLES ....................................... v LIST OF FIGURES ............................. vi ABSTRACT ........................................... vii INTRODUCTION ......................................... 2 Biological backround ............................. 4 Quantification of the gametogenic cycle .............. 7 Objectives . .................................. 9 METHODS ............................................. 10 Collection and processing .......................... 10 Quantification of the gametogenic cycle .............. 14 Variability within the mid-Atlantic ................. 16 Estimated bottom temperatures ...................... 17 Adductor muscle weight changes ..................... 18 RESULTS ............................................. 21 Quantification of the gametogenic cycle .............. 21 Variability within the mid-Atlantic ................. 29 Estimated bottom temperatures ...................... 42 Adductor muscle weight changes ..................... 43 DISCUSSION ........................................... 51 CONCLUSIONS ......................................... 64 LITERATURE CITED ...................................... 67 VITA ................................................ 74 i i i ACKNOWLEDGEMENTS I would like to thank my entire thesis committee. Bill DuPaul, Jim Kirkley, Bruce Barber, Gene Burreson, and Evon Ruzecki, for all the help and advice they have given to me from start to finish in this project. Special thanks to my major professor, Bill DuPaul, for suggesting this research topic, providing helpful suggestions along the way, and most importantly, for maintaining his constant enthusiasm for the scallop project. Thanks also to Jim Kirkley, for giving me a new insight toward fishery management, statistics, and computers. I am very appreciative to the owners, captains, and crews of all scallop vessels who donated sea scallops for this project. Without their support and interest, there would not be a scallop project. Much thanks go to all the students and staff in Advisory Services and elsewhere who continually offered their help with the seemingly endless scallop samples. This includes Lisa, Debbie, Katie, Ed, Charlie, Nancy, Art, Barbara, Cheryl, Maxine, Susan, Sue, Bob, Mike, Lee, Bruce, Jim, and Bill. This work was a lot more enjoyable because of them. I am especially grateful to Nita Walker, who cheerfully shared her expertise in histological techniques with me, and helped me throughout this study. I would also like to thank the staff in the computer room, photo lab, print shop, and word processing for their assistance in making this thesis presentable. Finally, I would like to express my deepest thanks to my family, for childhood memories of summers at the beach, where my love for marine science began, and for their continuous love and encouragement as I pursued my career in this field. To David, thank you for being here. This work was partially funded by the Virginia Sea Grant College Program, NOAA, Department of Commerce, under Contract # NA80AA-D-00021 and a Minor Research Grant from the College of William and Mary. i v LIST OF TABLES Page Date, location, and depth of histological samples 13 Samples for meat weight-gonad weight regression . 19 Summary statistics of pooled volume fractions . 23 Results of Wilcoxan paired sample test comparing gametogenic cycles between sex ............... 32 Summary statistics of volume fractions for individual areas ............................... 34 Results of Wilcoxan paired sample test comparing gametogenic cycles between areas ................. 37 Regression analysis of gamete weight and shell height 39 Samples for Wilcoxan paired sample test comparing gametogenic cycles between water depths .......... 40 Results of Wilcoxan paired sample test comparing gametogenic cycles between water depths .......... 44 Regression analysis of meat weight, shell height, and gonad weight ........ ........................ 48 Estimated adductor muscle weights and meat counts . 49 v LIST OF FIGURES Page Map of sampling a reas ....... ............... 11 Pooled total gamete volume fractions, both sexes 22 Pooled volume fractions of mature, resorbing, and developing gametes, both sexes .............. 25 Photomicrographs of mature and resorbing oocytes 27 Pooled volume fractions of follicle space and other structures, both sexes ............... 28 Pooled wet gonad weight for scallops in four shell height intervals .......................... 30 Pooled dry gonad weight for scallops in four shell height intervals .......................... 31 Mature gamete volume fractions of scallops at each sampling area, both sexes .............. 35 Mature gamete volume fractions of shallow and deep water scallops ........................ 41 Monthly estimated bottom water temperatures within the mid-Atlantic bight . ................... 45 Pooled adductor muscle weight for scallops of four shell height intervals ................. 47 vi ABSTRACT Information concerning reproduction is of vital importance for successful management of a fishery, especially when that fishery is regulated by the weight of a whole or partial organism. The harvest of sea scallops (P^ magellanicus) from the mid-Atlantic bight is regulated by a maximum average meat count. However, no documentation of the gametogenic cycle of sea scallops in this region existed in the literature. Therefore, this study was initiated to determine the gametogenic cycle of scallops in the mid-Atlantic bight. Histological quantification of gonadal tissue, as well as gonad weight changes, indicated that a semiannual gametogenic cycle was characteristic of sea scallops from the mid-Atlantic bight. Major spawnings occurred in May and November. Gonadal development and spawning in the spring comprised a longer period of time and resulted in greater fecundity. High variability in gametogenic processes was due to the lack of a distinct quiescent period between cycles and the sporadic occurrence of oocyte resorption and partial spawning of spermatozoa throughout the year. The timing of gametogenic processes between male and female scallops within each sampling area or month was very similar. Likewise, similar gametogenic cycles were observed throughout the mid-Atlantic bight, although some differences in the timing of gametogenic processes among areas and between depths were evident. Estimated bottom water temperatures were lowest in the summer and highest in the winter. The elevated temperatures in the winter were due to slope water intrusion onto the shelf, and may be responsible for semiannual spawning in the mid-Atlantic bight. A strong relationship between adductor muscle weight and gonad weight was verified in this study through regression analysis. Adductor muscle weights generally decreased as gonads developed, increased shortly after spawning, and continued to increase until gonads began to redevelop. The resulting variability and reduced size of adductor muscle weights caused by semiannual gametogenic activity creates increased difficulty for fishermen to comply with meat count regulations. However, semiannual spawning could result in increased recruitment, which would be beneficial to the fishery. Because semiannual gametogenic cycles are often subject to large interannual variability, researchers should continue monitoring gametogenesis of mid-Atlantic sea scallops for several additional years to verify the repeated occurrence and characteristics of the semiannual gametogenic cycle. Gonad weight changes would be an accurate and simpler method for a long term monitoring program. The results of this study should be recognized in the sea scallop fishery management plan if this fishery continues to be regulated by a maximum meat count. THE GAMETOGENIC CYCLE OF PLACOPECTEN MAGELLANICUS (GMELIN) IN THE MID-ATLANTIC BIGHT Introduction The sea scallop,