Stranding pattern and impact of fishing interaction in franciscana dolphin (Pontoporia blainvillei) in the north coast of São Paulo, Brazil – Contributions to the knowledge of the Franciscana Management Area (FMA IIa)

Abstract

This study presents the age structure and growth patterns, spatial and seasonal distribution, and anthropic interactions of franciscana dolphin Pontoporia blainvillei, using data from stranded individuals through a nine-year effort of daily monitoring on the northern coast of São Paulo, an important area within the Franciscana Management Area (FMA IIa). The main results are compatible with the literature for the region, i.e., asymptotic growth, sexual maturity, and seasonality of stranding events, except with a higher frequency of calves and adults on the north coast of São Paulo than observed in other areas. Our results strengthen the relevance of this FMA as a region with a high occurrence of franciscana strandings, in addition to highlighting the high occurrence of the species’ interaction with gillnet fishing. Approximately 60% of registered individuals presented evidence of fishing interactions. Ubatuba was the area with the highest concentration of events, underlining the need for studies on carcass drift dynamics, population structure, and local fishing, to determine the mortality cause of this species and the significant fishing threat locations.