Environmental and Individual Factors Shaping the Habitat Use and Trophic Interactions of Juvenile Bull Sharks (Carcharhinus leucas) in a Subtropical Estuary

Abstract

I would like to first thank Mike Heithaus, my major advisor, for taking a chance on a relatively inexperienced student, and giving him the opportunity to shine. You have been an excellent role model for me, both professionally and personally, and through your encouragement and guidance provided me with a means to pursue my career aspirations. Your levels of energy and excitement still surprise me, and the commitment to put toward your career and family have inspired me. Thank you for helping me develop both as a scientist and a person.I am forever indebted to Adam Rosenblatt for his unwavering support and assistance throughout my dissertation. Adam's door was always open and he was always willing to listen or discuss anything work-wise or of personal nature. You set a fantastic example, and through the many hours we spent alone on a boat, in the water, and in a tent you showed me the way of the world through the Everglades and Miami. Thank you for being so helpful and generous during our development together. otherwise. You will continue to inspire me to laugh every day and search for new places to explore and heights to climb. Michelle, you make me look on the bright side of things and are always the perfect partner in crime. Our lives will continue to intersect even after I move away. I could not have made it through these last six years without each of you. Therefore, elucidating the factors that drive persistent individual differences within populations is crucial for understanding how individuals, and in turn populations, will respond to environmental changes and anthropogenic stressors, and the implications of these responses for particular ecological functions. In this dissertation I investigated the movements, residency patterns, and trophic interactions of a juvenile bull shark (Carcharhinus leucas) population in a coastal estuary that serves as a nursery. I found that bull sharks undergo ontogenetic niche shifts in their diets and habitat use, with a gradual shift from using freshwater and estuarine resources to marine resources as sharks grew. This behavioral shift appeared to be driven by age-based differences in tradeoffs between safety from predators and availability of prey. Nested within population-level viii trends in behavior, there was considerable, and consistent, individual variation in both movements and trophic interactions suggesting individual specialization and divergent behavioral tactics within the population. Different behavioral types likely play different roles in food web connectivity and ecosystem dynamics, thus understanding the drivers and importance of phenotypic variability among species will be crucial for improving management strategies and predicting the responses of species and ecosystems to impending changes in environmental conditions and human impacts. ix Estuary relative to the availability of prey from surrounding marshes using acoustic 6 telemetry. I also compare stable isotope values from different tissues of sharks to make predictions about competing models of t...