Fishing gear ingestion by marine megafauna: Another threat to the South American sea lion Otaria flavescens

The South American sea lion, Otaria flavescens, is endemic to the Atlantic and Pacific coasts of South America, utilizing the southern Brazilian coast for resting and foraging. Due to the elevated biological productivity of the region, the fishing industry is one of the most important economic activities for the local human population. Gillnets and trawlers are the most prevalent fleets operating along the coastal region. The overlap between the foraging grounds of sea lions and fisheries leads to diverse interactions, with depredation being one of the most common, particularly in the case of gillnets. To evaluate and better comprehend this dynamic, a stomach content analysis was performed on sea lions washed ashore along the southern coast of Rio Grande do Sul in southern Brazil. The analysis focused on fragments of fishing gear that had been ingested. A total of 51 individuals were sampled through beach monitoring surveys, revealing that 16 (31.4 %) of them had ingested fragments of fishing nets. The predominant types identified were monofilament nets with mesh sizes of 90 mm, 100 mm, and 220 mm, corresponding to gillnet fisheries. GLMs showed that total length is a significant explanatory variable for both the presence and the weight of ingested fragments, likely reflecting a possible accumulation process over the animals’ lifetime. These results highlight the prevalence of interactions between southern Brazilian fisheries and sea lions, raising concern for this already impacted population.