Synthetic debris ingestion by carnivorous mammals in aquatic ecosystems: insights from the Eurasian otter (Lutra lutra) in Europe

Plastic pollution has become a global issue affecting many species. However, scientific knowledge is much more extensive in marine ecosystems than in freshwater and terrestrial environments, which results in a relatively limited amount information related to plastic interactions with species. The Eurasian otter (Lutra lutra) is a widely distributed mammal in European aquatic ecosystems and is currently classified as Near Threatened according to IUCN criteria. As a top predator in aquatic ecosystems, this species has been proposed as a sentinel for pollution, which poses a potential threat to this species. Here, we collected spraints from rivers of five European countries: Spain, Italy, Austria, Czechia, and the Netherlands. Synthetic debris was found in nearly 23 % of the samples analyzed, with fibres being the most common type detected. There was notable variation among countries, with Spain exhibiting the most diverse composition and highest quantities. We suggest that otters primarily ingest microplastics secondarily through their prey, with variations in microplastic presence influenced by local pollution sources and surrounding land use. Our study expands previous research on plastic debris in otter spraints by incorporating new populations and countries, but further research is needed to assess the broader impacts of synthetic debris on otters, particularly in underrepresented regions such as Asia and Africa.