Postmortem examinations show human activity impacts over half of seabirds beach-cast in Brazil

The Southern Atlantic Ocean is home to globally significant seabird populations, and off Brazil little is known about health condition in many species. Despite major known threats that these birds face (i.e., bycatch in fisheries, climate change, disease and pollution), plastic ingestion has become an emerging risk to seabirds, of which it is not clear how sublethal effects take part in the health of individuals that wash up along the coastline. Therefore, this study aimed to characterize seabird health of beach-cast seabirds in Brazil to understand how ingested plastic is related to cause of death and other pathologies. We reviewed complete postmortem examination records of 654 seabirds that beached between 2017 and 2021 in Southeastern Brazil. We identified a multitude of causes that lead to the beaching and death of wild seabirds, including natural and anthropogenic causes, and we also found that over half of analyzed seabirds were impacted by anthropogenic activity (fisheries, oil, plastic, and trauma). Fisheries foremost among them have been impacting seabirds in interactive ways, through bycatch, trauma, and by mismanaged associated debris. We found 5 % of birds that ingested plastic had potential debris obstruction in the gastrointestinal tract, and a possible relationship between ingested plastic and starvation either as a cause of death or as a pathological condition. This study highlights that seabird populations that beach in southeastern Brazil are subject to multiple and interacting threats from anthropogenic activities, providing recent data that can serve as baseline for awareness, conservation and public policies in the South Atlantic.