Microplastic pollution in an endangered Galapagos pinniped: A comprehensive regional assessment

Synthetic polymers are a persistent global threat to marine biodiversity, generating significant concern due to weak mitigation systems. This study aimed to assess microplastic (MP) ingestion in the endangered Galapagos sea lion (Zalophus wollebaeki), evaluating spatial patterns, polymer composition, and the influence of anthropogenic pressures and oceanographic drivers across the Galapagos Marine Reserve. We analyzed 160 scat samples from six rookeries across three Galápagos bioregions to quantify MP ingestion and evaluate regional sources and drivers using standardized digestion-based spectroscopic identification. MPs were detected in 44.4% of samples, with a mean abundance of 0.69 ± 1.06 particles per scat, dominated by fibers (91.8%) and dark colors (black: 44%, blue: 43%). MP abundance was higher at urban-adjacent and western-exposed rookeries (up to ∼1 MP scat^-1) compared to remote sites (∼0.5 MP scat^-1). μFT-IR analysis identified 12 polymer types, mainly cellophane (29%), polyethylene terephthalate (PET; 27%), and polyethylene-polypropylene copolymer (PP-PE; 14%), consistent with domestic and fisheries-related sources. However, generalized linear and multinomial regression models incorporating spatially explicit predictors across rookeries and foraging areas revealed no single dominant predictor, highlighting a complex interplay between local anthropogenic activities, oceanographic forces, and trophic adaptations. This multifactorial pattern suggests MPs reach this species through both chronic oceanic transport and localized pollution, modulated by prey diversity and foraging behavior of this species. These findings reinforce the vulnerability of pristine and remote ecosystems to global plastic pollution and call for conservation strategies that integrate land-based management, oceanographic dynamics, and species ecology.