Abstract
Analyzing the stomach contents of stranded cetaceans through the identification of otoliths can provide valuable insight regarding prey selection and habitat use. Identifying the prey species of cetaceans is critical as it sheds light on prey diversity, trophic transfer, and the capacity of cetaceans to respond to alterations in prey accessibility. This is especially important during environmental shifts, such as red tide blooms, that frequently occur in southwest Florida and are associated with unusual mortality events (UMEs). Florida Fish and Wildlife Conservation Commission’s Southwest Field Laboratory (FWC-SWFL) responds to stranded cetaceans and conducts necropsies, in which stomach contents are collected. FWC-SWFL staff and previous interns have created Standard Operating Procedures (SOPs) for the collection and processing of stomach contents, including the examination of jaw bones and otoliths. Additionally, an otolith reference collection has been created to guide identification of prey with the stomach contents collected. Building upon FWC-SWFL’s current SOP for the Collection and Processing of Stomach Contents and the otolith reference collection, the development of an SOP for the identification of otoliths using a dissecting microscope was created. Using stomach content samples from bottlenose dolphins (Tursiops truncatus) that stranded during the 2018 UME associated with a red tide event in southwest Florida, the new SOP focuses on how to utilize a dissecting microscope to identify and classify otoliths down to the lowest possible taxonomic level. Additional resources used for identification include peer-reviewed scientific literature, published reference materials, and the expertise of FWC Marine Mammal Research Biologist Emily Davidson. Creating an SOP for the use of a microscope for otolith identification as well as developing a dichotomous key and otolith identification log were the main objectives of this project. With the creation of this SOP in conjunction with the current SOPs and reference collection, stomach content analysis will continue to enhance dietary research in bottlenose dolphins in southwest Florida.