Defense Date

4-25-2023

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Derek Burkholder, Ph.D.

Second Advisor

Rosanna Milligan, Ph.D.

Third Advisor

Amy Hirons, Ph.D.

Keywords

Shark tagging, stable isotopes, Ginglymostoma cirratum, Carcharhinus plumbeus, Negaprion brevirostris

Abstract

Sharks, as well as other top predators, are in drastic decline worldwide. As apex and near-apex predators, species such as nurse, lemon, and tiger sharks maintain balanced marine ecosystems by enacting top-down trophic control. However, this cascading effect is diminished with exploitation via commercial and recreational fishing. Sharks are generally long-lived, mature late, have long reproductive cycles, and produce few offspring. Much remains to be learned about the community structure, population trends and conservation statuses of shark populations worldwide. Comprehensive studies on the composition of the shark community in Southeast Florida north of Miami have been limited. This study assessed the species composition and seasonal changes of the Southeast Florida shark community through a combination of drumline surveys and observation of seasonal intraspecific trophic changes via stable isotope analysis. The most common shark species encountered near coastal Southeast Florida included nurse sharks, sandbar sharks, lemon sharks, tiger sharks, and great hammerhead sharks. Catch per unit effort (CPUE) was greater during most rainy seasons (June through November) compared to most dry seasons (December through May), though not significantly. Most of the study species displayed overlap in trophic niches, and some exhibited significant seasonal differences in carbon, but not nitrogen, stable isotope ratios as well. While CPUE did not change significantly between seasons, the effects of seasonality and water depth significantly influenced the total number of sharks captured throughout the study.

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