Occurrence of cetacean strandings on the coast of São Paulo, Brazil: a spatio-temporal assessment from 2017 to 2021

Abstract

This study is part of the Projeto de Monitoramento de Praia– Bacia de Santos - (PMP-BS, Santos Basin Beach Monitoring Project) and is based on data from stranded cetaceans collected during beach monitoring in the state of São Paulo, between 2017 and 2021. Our aim was to assess the temporal and spatial patterns of strandings, including the main recorded species, stranding locations, and their distribution throughout the year. The analysis covered 258 beaches along the coast of São Paulo, which was divided into three mesoregions: South Coast (LSP), Central Coast (LCP), and North Coast (LNP). We calculated the number of regularly monitored beach kilometers and the number of cetacean records for each of these mesoregions. These records were termed ‘Strandings per Unit of Sampling Effort’ (EPUE). The total regular daily monitoring covered 430,596.36 kilometers along the beaches, with a record of 2,055 stranded individuals belonging to 18 cetacean species. On average, there were 411 ± 38 stranded individuals per year, ranging from 387 in 2019 to 470 in 2021. The species most frequently encountered were Franciscana dolphin (Pontoporia blainvillei), Guiana dolphin (Sotalia guianensis), humpback whale (Megaptera novaeangliae), and Atlantic spotted dolphin (Stenella frontalis). The Franciscana and Guiana dolphins accounted for 86% of records. Forty-three percent of strandings (877) was located in LSP , 33% (670) in LCP, and 25% (508) in LNP. These results were expected and supported by previous studies, as LSP encompasses important priority conservation areas with a diversity of ecosystems and the presence of endemic and endangered species. Keywords: beach monitoring, cetaceans, conservation, mesoregions, São Paulo coast, strandings