Spatial variation in trophic interactions of bottlenose dolphins (Tursiops truncatus) within the Florida Coastal Everglades assessed with stable isotopes

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Valeria Paz, Biological Sciences, Florida International University, Miami, FL, Michael R. Heithaus, Florida International University, Miami, FL and Jeremy Kiszka, Biological sciences, Florida International University, Miami, FL

Background/Question/Methods
Bottlenose dolphins (Tursiops truncatus) are an upper trophic level predator of the Florida Coastal Everglades (FCE), which is comprised of multiple habitats including creeks, rivers, shallow inland bays that feature numerous mangrove islands, and the coastal oceans of the Gulf of Mexico and Florida Bay. As an abundant predator throughout the FCE, bottlenose dolphins could play important roles in the ecosystem through both top-down and bottom-up pathways. To date, however, little is known about trophic interactions of dolphins in the FCE and how they might vary within and among habitats. Bulk stable carbon (δ13C) and nitrogen (δ15 N) isotope analysis of skin and blubber biopsy samples (n=90) were used to investigate trophic interactions of dolphins across four major habitats of the FCE. These habitats, including mesohaline rivers ( n= 13), an inland low-salinity bay ( n=5), a coastal oligohaline bay ( n= 37), and marine waters of Florida Bay ( n= 18), and the Gulf of Mexico ( n=16), have food webs that are isotopically distinct.
Results/Conclusions
Values of δ15N suggest that dolphins feed at a similar trophic level system-wide. Unlike other top predators studied in the FCE (e.g., bull sharks, American alligators), however, δ13C values suggest that bottlenose dolphins appear to restrict their foraging within the habitats where they were sampled. Estimated age for each sampled individual using DNA methylation methods suggest that trophic interactions did not vary significantly with age. Our results suggest that bottlenose dolphins likely form multiple discrete foraging communities across the FCE but may play different ecological roles across these foraging locations.