Concentrations of Microplastics in Sphyrna tiburo Gastrointestinal Tracts from Tampa Bay, Florida

Marine microplastics are global and have widespread effects on marine biota. Limited research has been conducted on assessing microplastic concentrations in benthic sharks. As the only omnivorous shark, bonnetheads (Sphyrna tiburo) serve as an indicator species for ecosystem health in Tampa Bay, Florida. Bonnetheads make an ideal candidate for quantifying microplastic (<5mm) concentrations in coastal habitats, as they may directly ingest microplastics adhering to seagrass blades, or indirectly through their diet of crustaceans. Thus, examining the contents of their stomachs can reveal important insight into the concentration and composition of microplastics at and near the seafloor, which remains an understudied section of microplastic research. Gastrointestinal (GI) tracts (cardiac stomach, pyloric stomach, spiral valve intestine, and colon) of seven bonnethead sharks collected from June - November of 2025, as part of long-term monitoring in Tampa Bay by the Florida Fish and Wildlife Conservation Committee (FWC) were analyzed. Specimens examined were male, female, juvenile, and adult ranging in size from 48.2 - 94.5 cm. Microplastic particles found in the GI tracts were predominantly small particles (20 - 100 µm), however several larger particles were also detected. Most of the larger particles appear to be fishing line. These findings indicate that microplastics are prevalent in coastal benthic environments in Tampa Bay and suggest that future research is needed on the long-term effects of ingestion of microplastics in bonnetheads.