Spatio-temporal patterns of franciscana dolphins and overlap with offshore wind farm areas in southern Brazil

The franciscana dolphin Pontoporia blainvillei is an endemic cetacean of the southwestern Atlantic Ocean and is recognized as one of the most threatened cetacean species in the region, primarily attributable to incidental catches in fisheries throughout its distributional range. Furthermore, coastal development, including the establishment of offshore wind farms (OWFs), may pose additional threats to the species. This study aimed at evaluating the distributional patterns of franciscana in Rio Grande do Sul State (RS), southern Brazil, utilising 2 distinct data sources: fishery-dependent data (bycatch records) and fishery-independent data (aerial surveys). We further assessed the predicted abundance of the species in relation to areas claimed for OWF development along the entire RS inner continental shelf. Given the divergent spatio-temporal characteristics of the data sets, we employed 2 distinct methodological approaches to generate statewide species distribution prediction maps. Data convergence was examined using a modified t -test. Results indicated that the data sets did not converge with respect to density estimates; however, both methods identified congruent spatial patterns, delineating comparable areas of elevated species occurrence. The highest densities were observed in estuary-influenced areas, near the Mampituba River in the northern sector, and the Rio Grande breakwaters and Albardão Lighthouse in the southern sector. The spatial overlap between areas of elevated density and proposed OWF sites suggests potential spatial conflict. These findings underscore the necessity for comprehensive spatial assessments to inform conservation strategies and guide the planning of offshore wind energy development in the region.