Identifying priority areas using a multispecies approach for the conservation of marine megafauna species vulnerable to bycatch in commercial gillnet fisheries

Bycatch is one of the main causes of mortality among marine megafauna around the world. In the coastal waters of southern Brazil, bycatch in gillnet fisheries affects threatened species that use this region as a breeding and feeding area. The identification of hotspot areas of bycatch is necessary to design and prioritize efficient spatial–temporal closures that protect the largest possible number of threatened species of marine megafauna. In this context, the use of a multispecies approach is an important step towards planning effective fisheries management measures. This study has two main objectives: (1) to identify hotspot areas of bycatch in gillnet fisheries for the most threatened marine megafauna species on the continental shelf of Rio Grande do Sul (RS); (2) compare single species and multispecies mapping methods for the identification of these areas. To meet these objectives, data collected by onboard observers during fishing trips in the coastal commercial RS-based gillnet fleet between 2013 and 2015 and between 2018 and 2020 were analyzed. For the identification of the areas, hierarchical Bayesian spatio-temporal models were implemented, using monospecific and multispecific approaches and a weighting system for the conservation status of the species. Both approaches provide similar results, identifying three bycatch hotspots according to the time frame analysed. Based on our findings, we propose these areas as the top candidates for fishing exclusion zones, based on their biodiversity value. The suggested spatio-temporal closures would benefit several endangered species while also contributing to the recovery of fish populations.