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Mariah Beck, Senior Honors Thesis 2016, Archive Copy Juvenile Wild Lemon Shark (Negaprion brevirostris) Health Assessment: Establishing a Baseline and Assessment Procedure for the Health of the South Caicos Juvenile Lemon Shark Population Senior Thesis Presented to The Faculty of the School of Arts and Sciences Brandeis University Undergraduate Program in Biology Professor James Morris, Advisor In partial fulfillment of the requirements for the degree of Bachelor of Science By Mariah R. Beck April 2016 Copyright by Mariah R. Beck !ii Abstract Shark health is very important to the health of marine ecosystems, but it has been minimally studied in the past. In this study, a new health assessment procedure was established by combining traditional methods of overall health assessment, such as condition factor, with newer methods focused on parasitic parameters, such as fin rot infections and ectoparasites. This study indicates that condition factor may decrease and fin rot may increase with increased shark recaptures. Also, female sharks may experience more intensive fin rot than males and the left side of the first dorsal fin may be more susceptible to fin rot as well. Dermophthirius nigrelli monogenean flatworms, Stibarobdella macrothela leeches, and Rocinella signata isopods were found only on sharks exhibiting fin rot which may support the hypothesis that certain parasites increase shark susceptibility to other parasites and infections by decreasing immunity or acting as vectors. Analysis of these findings established a baseline for the juvenile lemon shark population in South Caicos, Turks and Caicos Islands. This population is in relatively good health and should be monitored for changes as coastal development continues on this island. It may act as good model for the effects of coastal development on shark populations and marine ecosystem health in the future. For continued monitoring of this population, condition factor measurements should be combined with fin rot analysis and ectoparasite observations as demonstrated in this study. !iii Acknowledgments A special thank you is extended to Professor James Morris for his continued and thoughtful support throughout my work on this project. I would also like to thank Brandeis University and the Brandeis undergraduate Biology department for their support. The technical support provided by the School for Field Studies for this research is gratefully acknowledged. Special gratitude is also extended to Dr. Aaron Henderson and Travis Gomez-Phillips without whom this research would not have been possible. Thanks is also extended to the students at the School for Field Studies for continued support during data collection and to the Turks and Caicos Islands government for allowing this research to take place. !iv Table of Contents Acknowledgments……………………………………………………………………..…………ii List of Tables………………………………………………………………………………………v List of Figures…………………………………………………………………………………….vi I. Introduction………………………………………………………………………………..…..1 The Bell Sound Nature Reserve, South Caicos, Turks and Caicos Islands, British West Indies…………………………………………………………………………………………..… 3 The Lemon Shark, Negaprion brevirostris………………………………………………..4 Lemon Shark Reproduction and Juvenile Behavior………………………………………7 Threats to Lemon Sharks………………………………………………………………….9 Health Impacts of Research Capture/Handling Procedures……………………………..10 Major Shark Capture Methods…………………………………………………………..13 Condition Factor…………………………………………………………………………15 Parasites: Fin Rot, Monogeneans, Isopods, & Leeches……………………..…………..16 Research Outline..….…………………………………………………………………….23 II. Materials & Methods…………………………………………………………………..……25 Study Area………………………………………………………………………………..25 Capture Method………………………………………………………………………….25 General Data Collection………………………………………………………………….26 Condition Factor: Data Collection and Analysis……………………………………..…26 Fin Rot: Data Collection and Analysis…………………………………………………..27 Ectoparasites: Data Collection and Analysis…………………………………………….28 !v III. Results………………………………………………………………………………………29 No significant difference in condition factor was found between shark sexes and no significant correlation was found between condition factor and shark size…………..…29 Condition factor may decrease with increased number of recaptures……………..…….30 The intensity of fin rot is low overall and no significant correlation was found between condition factor and fin rot intensity……………………………………………………..31 Fin rot surface area may increase with the number of recaptures, female sharks may experience higher intensity fin rot, and left fin surfaces may be more susceptible to fin rot………………………………………………………………………………………..32 Certain parasites may increase the prevalence of other parasites, and some parasites are found in specific regions of a shark………………………………………………..……34 IV. Discussion……………………………………………………………………………….….37 Condition Factor…………………………………………………………………………37 Fin Rot………………………………………………………………………………..…39 Ectoparasites……………………………………………………………………………..42 Conclusion……………………………………………………………………………………….45 References………………………………………………………………………………………..46 !vi List of Tables Table 1. List of data collected upon capture of a shark specimen in the field………………….26 Table 2. Prevalence, Mean Intensity, and Abundance of Parasites: Parameters for analyzing the infection rates and intensity of leeches (Stibarobdella macrothela), monogenean flatworms (Dermophthirius nigrelli), and isopods (Rocinella signata)…………………………………… 35 !vii List of Figures Figure 1. Map of the Turks and Caicos Islands geographic region…………………..……..……3 Figure 2. Map of the Turks and Caicos Islands, highlighting South Caicos………………………3 Figure 3. Bell Sound Nature Reserve on South Caicos…………………………………………..3 Figure 4. Identifiable features of the lemon shark: (a) similarly sized dorsal fins (b) blunt, round snout (c) yellow-brown hue…………………………..……………………..……………5 Figure 5. Global distribution of lemon sharks…………………..………………………………..6 Figure 6. Mangrove trees dominating a nursery habitat…………………………………………..7 Figure 7. Gill Net Capture Method…………………………………………..…………………..14 Figure 8. Long Line Capture Method…………………..………………………………………..14 Figure 9. Condition factor grouped frequency distribution shows variable health with a potential tendency towards the lower end of the health range……..…..…………….…..29 Figure 10. Mean condition factor for sharks recaptured once, twice, three times, and four times shows a possible trend of decreasing condition factor with increased number of recaptures. Note: only one specimen was recaptured four times and the recorded condition factor for that specimen was utilized in this graph……………………………30 Figure 11. Percent of captured sharks that experienced an increase, decrease, no change, or inconsistent change in condition factor between recaptures over time shows the highest percentage of sharks experienced decreased condition factor between captures. Note: N/A represents sharks that were missing data essential for the condition factor calculation………………………………………………………………………………..31 !viii Figure 12. Median degree of change for sharks that experienced an increase (I) and decrease (D) in condition factor between recaptures shows that condition factor increases were larger on average than condition factor decreases between captures…………………………..31 Figure 13. Fin rot surface area ratio grouped frequency distribution shows a generally low degree of fin rot in this population………………………………………………………………32 Figure 14. Percent of captured female and male sharks shows that more females were captured than males………………………………………………………………………………..33 Figure 15. Mean fin rot surface area ratio (± SD) for female and male captured sharks shows that females may generally experience more intense fin rot than males……………………..33 Figure 16. Specimen BSNR023 exhibiting highly variable fin rot between the two sides of the same first dorsal fin…………………………………………………………………..34 Figure 17. Two Dermophthirius nigrelli monogenean parasites (BSNR023)……….………..…35 Figure 18. One Stibarobdella macrothela leech collected from BSNR024…………….….….…36 Figure 19. Front (A) and back (B) view of one Rocinella signata isopod collected from BSNR013. Note: the distinctive half-moon pattern located towards the posterior end of the specimen is distinct and helpful for species identification (C)……………………..36 !1 I. Introduction Human beings have an incredibly unique relationship with sharks – Jaws or Discovery Channel’s Shark Week might come to mind – but these animals are also one of the most important groups of animals for the health of the oceans worldwide, especially because they can greatly impact many species populations cascading down the food chain below them. Many people do not see themselves connected to marine ecosystems, but human survival is indeed linked to the health of the world’s oceans. Oceans provide human beings with air to breathe, food to eat, and a source of climate stability on Earth. This vital resource is a system of diverse marine ecosystems, many of which are put at great risk when shark populations are threatened. This is because shark population changes have significant domino effects on the rest of the ecosystem’s food chain. Sharks have been widely studied for this reason, but shark health specifically has been minimally explored, especially in wild shark populations. It is often difficult to study wild sharks in their natural environment because of their large size, free-ranging behavior, and the relative inaccessibility of the ocean for scientists (Sundstrom et al. 2000). Although wild shark health evaluation studies have been particularly infrequent, there is an important and increasing
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