| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2023 Microplastics pose a significant threat to marine ecosystems across multiple trophic levels. Spotted seals (Phoca largha) are piscivorous and occupy one of the higher trophic positions in the Bering and Chukchi seas, putting them at risk of ingesting microplastics through prey. This project aimed to determine if microplastics are present in the stomachs of spotted seals harvested for subsistence purposes and compare their presence spatially between two harvest locations, Gambell and Shishmaref, AK. Microplastics are predicted to increase in the Arctic over time due to climate warming and subsequent deposition of microplastics from melting sea ice. Therefore, we examined stomachs from 2012 and 2020 to explore temporal changes. Furthermore, as spotted seal pups (<1 yr of age) and non-pups forage differently, we expected a difference in microplastic ingestion between age classes. We processed stomachs using enzymatic digestion and vacuum filtration. Use of the enzyme digestion method enabled microplastic detection while preserving the hard parts of prey items (e.g., fish otoliths and shrimp carapaces) for diet analysis. We then examined filters with a stereomicroscope, and calculated microplastic frequency of occurrence (FO). A total of 34 (16 from 2012 and 18 from 2020) stomachs from Gambell and Shishmaref have been examined, and a total of 211 microplastic particles were isolated from 33 stomachs (97.1% FO), containing 1 to 23 particles per stomach. Our analysis showed no significant difference in FO between pups and non-pups, between the two harvesting locations, or between harvest years. Additionally, there was no significant difference in the microplastic concentration among the spotted seal stomachs examined in this study. Our data indicate that microplastic ingestion has not changed in frequency between age class, harvest location, or year. This baseline study was successful in isolating microplastics in the stomachs of spotted seals and showed that ...
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