Marine mammal strandings provide unique opportunities to acquire information about cryptic animals that would otherwise be difficult to access in the wild. Assessing stomach contents of stranded marine mammals has provided insight into the diet of many species. An understanding of diet composition is essential to assess habitat use and quality, energetics, and nutrient requirements relevant to various life history stages. Studies of cetacean stomach contents not only provide important clues regarding habitat use and ecosystem stability, but can also enhance conservation efforts by identifying high value habitats and predicting how various species may respond to shifts in prey availability. These studies are especially important to monitor dietary shifts during times of trophic cascade alteration, such as harmful algal blooms. Beginning in November 2017, the southwest coast of Florida has been experiencing a harmful algal bloom of the toxin producing dinoflagellate, Karenia brevis. The occurrence of this bloom provided the opportunity to assess dietary shifts during a red tide event, which is the suspected cause of a multispecies unusual mortality event in southwest Florida. The stomach contents of 20 bottlenose dolphins (Tursiops truncatus) that stranded in southwest Florida from August 2016 to August 2018 were collected during necropsy and then frozen for future processing and analysis. After the successful processing of 3 stomach content samples, a standard operating procedure was written to ensure consistent collection and processing of current and future stomach content samples at the Florida Fish and Wildlife Conservation Commission’s Southwest Field Lab (FWC-SWFL). This standard operating procedure was followed to process the remaining 17 stomach content samples. Furthermore, a training workshop was organized and held for dedicated volunteers and FWC-SWFL staff to ensure the longevity of this project and future research opportunities. Based on gross observations of partially digested prey items, skulls, jaw bones, and otoliths, there appeared to be a slight shift in prey families consumed by bottlenose dolphins in southwest Florida during the current red tide event. A novel finding in the stomach contents of stranded bottlenose dolphins during this red tide event were members of the family Ophichthidae, or snake eels. Stomach contents of dolphins that stranded prior to the presence of a red tide bloom did not include snake eels, but X stomachs of dolphins that stranded during the presence of a red tide bloom contained one or more. However, stomachs of dolphins that stranded during both the presence and absence of the red tide bloom contained common prey families such as Sparidae, Clupeidae, and Scianidae. Many marine mammal species are recognized as sentinel species, and the diets of these apex predators have the potential to reveal valuable information concerning ecosystem stability in an increasingly degrading environment. The identification of prey species among stranded cetaceans across this time span will facilitate analyses of prey seasonality, species diversity, predator demographics, human interaction, and various other factors. Moreover, this information will contribute to an improved understanding of the foraging habits of bottlenose dolphins in an area that is often affected by red tide blooms.
Davidson, Emily, "Stomach content analysis of stranded bottlenose dolphins (Tursiops truncatus) in southwest Florida from 2016-2018" (2018). Internship Reports (Restricted). 321.
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