Microplastics in spotted seal stomachs from the Bering and Chukchi seas in 2012 and 2020

Microplastics are found throughout marine environments, including the Pacific Arctic. Given their ubiquity, it is important to understand how microplastics biomagnify through food webs and accumulate in upper trophic level organisms, such as marine mammals. Spotted seals (Phoca largha) occur throughout the Bering, Chukchi, and Beaufort seas of the Pacific Arctic and are harvested for subsistence by many Alaska Native communities. We examined stomachs of subsistence-harvested spotted seals for microplastic presence and compared between age class (pups <1 yr and non-pups ≥1 yr), harvest location (Gambell and Shishmaref, Alaska, USA), and harvest year (2012 and 2020). We processed stomachs using enzymatic digestion and vacuum filtration, enabling microplastic detection while preserving prey hard parts (e.g., fish otoliths) for diet analysis. Filters were inspected and microplastic concentration was calculated for each stomach. We examined 34 (16 from 2012 and 18 from 2020) stomachs from Gambell and Shishmaref, and 33 (97.1 %) stomachs contained 1 to 23 particles for a total of 190 microplastics. No significant difference in microplastic concentration was found between age class, harvest location, or year. This baseline study showed that similar levels of microplastics have been ingested by spotted seals for at least a decade. Furthermore, we found more microplastics in spotted seal stomachs that had either benthic prey or higher trophic prey (i.e., fish). Further study of microplastic ingestion is needed to assess health impacts to spotted seals, other ice-associated pinnipeds, and subsistence users that serve as indicators of ecosystem health in the Bering and Chukchi seas.