Assessing anthropogenic microparticle contamination in the stomachs of salmon sharks

Anthropogenic microparticles, including microplastics, have become a pervasive, global environmental issue in all biomes. In marine systems, their impacts on large pelagic predators remain poorly quantified, limiting our ability to understand exposure pathways and ecological consequences. Salmon sharks ( Lamna ditropis ), regionally endothermic predators in the North Pacific, may be vulnerable to microparticle ingestion due to their high energetic demands, broad diet, and exploitation of coastal and offshore habitats known to contain relatively high amounts of pollution. To assess exposure in this species, we analyzed stomachs from 18 salmon sharks collected off the Oregon coast between 2022 and 2024 and evaluated differences across ontogenetic and sex classes as well as microparticle counts in their prey. Anthropogenic microparticles were found in every shark stomach, with an average (± SD) of 25.6 ± 23.0 microparticles per stomach. Anthropogenic microparticles were dominated by fibers and fragments, with white and black being the most common colors. µFTIR spectroscopy confirmed approximately 16% of anthropogenic microparticles were synthetic polymers, primarily polyethylene, polypropylene, and polyamide, while the remainder consisted largely of anthropogenic cellulose with spectra most similar to cotton. Microplastics were detected in all but three stomachs, yielding an 82.4% detection frequency of plastics. Relative to other elasmobranch studies, salmon sharks exhibited universally high detection frequencies and elevated particle burdens. This study provides the first evidence of microplastics and anthropogenic microparticle ingestion in salmon sharks and contributes to the growing body of literature documenting exposure in large pelagic predators.