Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2002 Feeding habits of blacktip sharks, Carcharhinus limbatus, and Atlantic sharpnose sharks, Rhizoprionodon terraenovae, in Louisiana coastal waters Kevin Patrick Barry Louisiana State University and Agricultural and Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Oceanography and Atmospheric Sciences and Meteorology Commons Recommended Citation Barry, Kevin Patrick, "Feeding habits of blacktip sharks, Carcharhinus limbatus, and Atlantic sharpnose sharks, Rhizoprionodon terraenovae, in Louisiana coastal waters" (2002). LSU Master's Theses. 66. https://digitalcommons.lsu.edu/gradschool_theses/66 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. FEEDING HABITS OF BLACKTIP SHARKS, CARCHARHINUS LIMBATUS, AND ATLANTIC SHARPNOSE SHARKS, RHIZOPRIONODON TERRAENOVAE, IN LOUISIANA COASTAL WATERS A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College In partial fulfillment of the Requirements for the degree of Master of Science in The Department of Oceanography and Coastal Sciences by Kevin P. Barry B.S., University of South Alabama, 1996 August 2002 AKNOWLEDGEMENTS I would like to first and foremost thank my major professor, Dr. Richard Condrey, for giving me the opportunity to pursue this graduate degree. His willingness to accompany me during sampling trips, his enthusiasm and interest in my research topic, and his guidance throughout my time here has forged more than a major professor/graduate student relationship; it has formed a friendship as well. I would also like to thank the members of my committee, Dr. Bruce Thompson, Dr. Charles Wilson, and Dr. Oscar Huh. Special thanks go to Dr. Thompson for help regarding laboratory analysis. Thanks also go to Dr. James Geaghan for his assistance on selecting appropriate analyses for my data. This project was funded by Coypu Trust foundation. On behalf of the entire shark “team”, I would like to extend my thanks for providing the financial assistance for a study that we consider to be meaningful for habitat and fisheries management purposes. I would like to extend a special thanks to everyone who assisted in the field work: Gary Peterson, Jason Blackburn, Julie Neer, John Plunket, Brett Blackmon, Chrissy Bush, and anyone who I may have unintentionally overlooked. A special thanks to Gary for use of his fishing tackle and for being as enthusiastic (although not quite as good) a fisherman as me. Additional thanks are needed for Jason, as well, for supplying me with maps that I used for presentations and my thesis. Thanks to Marty Bourgeois of Louisiana Wildlife and Fisheries for reviewing my summary regarding the abundance of organisms in my sampling area. Thanks go to Charles Sasser, Guerry Holm, Jr., and associated staff of the Coastal Ecology Institute for use of the vegetation laboratory for processing many of my samples. ii Even though shark stomach contents are not the most pleasant smelling things, I never heard a complaint from them for using the lab. Thank you to Carol Fleeger, who always made sure I was following the correct university procedures, and who always had an answer for no matter what kind of question I threw at her. Thank you to Sean Keenan for putting up with my endless questions on deadlines and feeding study analysis techniques. He was always able to put things in a way that I could understand them. Thanks to Brian Milan for making me feel welcome when I arrived here, and for all the cook-outs at his house that gave me a chance to relax and an escape from the endless grind that is graduate school. Huge thanks go to my parents, Wilfred and Sharon Barry, for giving me the support, encouragement, and freedom to pursue my dreams. Special thanks go to Dad for sharing with me his love of the water at an early age, which has ultimately brought me to where I am today. Final thanks must go to my fiancée, Carrie Sinclair, who shares my passion for marine biology, and who gave me motivation to complete this degree so that we may start the next phase of our life together. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ………………………………………………………………..…ii LIST OF TABLES …..………………………………………………………………………..v LIST OF FIGURES ………….………………………………………………….……………vi ABSTRACT ..…………………………………………………………………………..…...viii INTRODUCTION ………..….………………………………………….…………………….1 MATERIALS AND METHODS .………………………………………….…………………5 Study Site ….………………………………………………………………….………5 Field Procedure ……………….………….…………………………………...………8 Laboratory Procedure ………………………………………….…………………….14 Statistical Analysis …………………………………………………………………..16 RESULTS……………………………………………………………………………………19 Stomach Content Analysis ………………………………………….……………….22 Scale of Degradation Derivation …………………………………………………….36 Diel Feeding Determination …………………………………………………………38 Gastric Evacuation Rate Calculation…………………………………………………47 Growth Rate Calculation……………………………………………………………..54 Growth Efficiency Estimation ……………………………………………………….56 DISCUSSION ………………………………………………………………………………..62 BIBLIOGRAPHY…...………………………………………………………………………..69 VITA ……………………………………………...………………………………………….72 iv LIST OF TABLES 1. Idealized general gillnet sampling schedule for May and September 2001 in Timbalier Bay, Louisiana….…………………………………………………10 2. Idealized general gillnet sampling schedule for June-August 2001 in Timbalier Bay, Louisiana……………………………………………….…………….11 3. Date, general area, coordinates, time interval, total set time, and the number of blacktips captured for each set of the gillnet for the year 2000…………………………………………………………………….………..20 4. Date, general area, coordinates, time interval, total set time, and the number of blacktips captured for each set of the gillnet for the year 2001……………………………………………………………………………...21 5. Summary statistics by time interval for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001…...……………………………………………………23 6. Summary statistics by month for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001…..………………………………………………………….24 7. Summary statistics by time interval for Atlantic sharpnose caught in Timbalier Bay, Louisiana, in 2000-2001...…………………………………………...25 8. Summary statistics by month for Atlantic sharpnose caught in Timbalier Bay, Louisiana, in 2000-2001.…………………………………………….26 9. Diet composition of blacktips caught in Timbalier Bay, Louisiana, in 2000-2001……………………………………………………………………….....27 10. Diet composition of Atlantic sharpnose in Timbalier Bay, Louisiana, in 2000-2001…………………...……………………………………………………..31 11. Description of each category in the Scale of Degradation for menhaden found in the stomachs of blacktip sharks caught in Timbalier Bay, Louisiana, in 2000-2001……………………………………………….……………..37 v LIST OF FIGURES 1. Gillnet sampling locations (denoted by an S) in Timbalier and Terrebone Bay, Louisiana, in 2000……….……………………………………………6 2. Gillnet sampling locations (denoted by an S) in Timbalier Bay, Louisiana, in 2001……………..……………………………………………………….7 3. Graphical representation of prey items from the stomachs of blacktips caught in Timbalier Bay, Louisiana in 2000-2001……………..…………..30 4. Graphical representation of prey items from the stomachs of Atlantic sharpnose caught in Timbalier Bay, Louisiana, in 2000-2001…………………………………………………………………………….34 5. Comparison of the diet composition of blacktips and Atlantic sharpnose in Timbalier Bay, Louisiana, in 2000-2001 according to prey family………………………………………………………………………....35 6. Plot of log (shark weight) versus log (shark length) with an overlay of the predicted regression line for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001……………………………………………………………...39 7. Plot of shark weight in grams (skw) versus shark length combined with a plot of the weight of the stomach contents in grams multiplied by 10 (ttpw) versus shark length for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001………………………………………………………...40 8. Plot of the Index of Relative Fullness (Irf) versus shark length for blacktips caught in Timbalier Bay, Louisiana, in 2000-20001…………………….…42 9. Plot of the estimates of the Index of Relative Fullness (Irf) versus time interval for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001…………………………………………………………………….……43 10. Plot of the actual values of the Index of Relative Fullness (Irf) versus time of capture (Tc) for blacktips with partially open umbilical scars overlayed with a plot of the predicted values of Irf for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001…..……….………..45 vi 11. Plot of the actual values of the Index of Relative Fullness (Irf) versus time of capture (Tc) for blacktips with healed umbilical scars overlayed with a plot of the predicted values of Irf for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001….……………………………….46 12. Plot of the number of total stomachs and empty stomachs versus time interval for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001…..………………………………………………………………………...48 13. Plot of the percentage of empty stomachs versus time interval for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001………………………...49 14. Plot of the Index of Relative Fullness values (Irf) versus Scale of Degradation for blacktips caught in Timbalier Bay, Louisiana, in 2000-2001…………………………………………………………………………….50 15. Three-dimensional plot