Spatio-temporal distribution of franciscana (Pontoporia blainvillei) bycatch in the coastal gillnet fisheries operating and strandings along the coast of Rio Grande do Sul, Brazil

Abstract

This study aims to describe spatio-temporal patterns in bycatch and strandings of franciscanas, Pontoporia blainvillei, as well as of net settings of the coastal commercial gillnetting fleet operating off central and southern Rio Grande do Sul coast. This commercial gillneting fleet is responsible for high incidental takes of the species. A total of 690 net settings made by 23 fishing boats resulted in 136 bycatches from January 2002 to December 2003. For the same period 348 strandings were recorded. These data were plotted in georeferenced maps, split in 20x20km grids for each season. Despite some seasonal and year-to-year variation in preferential fishings areas, they are widely distributed in the inner continental shelf off central-southern Rio Grande do Sul. Nevertheless, the bycatch rate was higher between Chui and Albardão lighthouse (KW=13.958, gl=5, p=0.01). And there is a strong correlation between strandings and wind force (rs, r=-0,73; p<0,05).