Seabird strandings on the Brazilian coast: What influences spatial and temporal patterns?

Seabirds exhibit physiological adaptations that allow them to forage in the marine environment and undertake long-distance migrations during non-reproductive periods. As a result, they face various natural and anthropogenic pressures, which can lead to extreme fatigue and even death. Stranded bodies that float in the sea can wash ashore, providing valuable ecological information. This study aimed to analyze seabird strandings along the south and southeast coasts of Brazil between 2016 and 2019, focusing on spatiotemporal and potential environmental and anthropogenic influences. Using data from the Santos Basin Beach Monitoring Project, we calculated ecological indices of abundance, richness, and diversity for the entire seabird community and separately by migratory behavior (resident, southern migratory, northern migratory). Statistical modeling revealed a strong decreasing trend in strandings from south to north, with higher events on the southern coast (Santa Catarina and Paraná) and lower on the southeast coast (São Paulo). Resident species and northern migratory species showed peak strandings in spring, while southern migratory peaked in winter. These spatial and temporal patterns reflected birds' home ranges, reproductive cycles, and migratory behaviors. Environmental variables influenced strandings differently depending on species migration behavior and ecological indices, highlighting the role of oceanographic processes in carcass drift and the impact of climatic events on species mortality. This study is the first to demonstrate a spatiotemporal pattern of seabird strandings on the Brazilian coast, providing valuable insights into seabird dynamics in the Santos Basin and offering important data for conservation efforts.