Definition of no-fishing zones and fishing effort limits to reduce franciscana bycatch to sustainable levels in southern Brazil

Franciscana Pontoporia blainvillei bycatch has been high for near six decades in western South Atlantic, with large regional variation. In 2012, the Brazilian Government-regulated gillnet fisheries in south and southeast Brazil by reducing fishing effort and establishing no-fishing zones. However, there is evidence that the magnitude of franciscana bycatch remains high and unsustainable. The aims of this study were to identify hotspot areas of franciscana bycatch associated with two main gillnet fisheries and to propose no-fishing zones combined with limited total allowable fishing effort (i.e. total net length per season) in order to meet management objectives in southern Brazil. A hierarchical Bayesian model using integrated nested Laplace approximation (INLA) was employed based on 1427 reported settings from 1999 to 2003 and 2006 to 2009. Hotspot zones were detected and are proposed as no-fishing zone during the white croaker Micropogonias furnieri and striped weakfish Cynoscion guatucupa gillnet fishing seasons. Their extents represent 6% (1466.8 km(2)) and 19% (4493.7 km(2)) of the fishing ground (23 204.1 km(2)) during croaker and weakfish fishing seasons respectively. The total allowable fishing effort estimated outside the no-fishing zones were estimated at 541 km (95% credible interval (CrI) [339; 940]) during croaker and 688 km (CrI [312; 2,166]) during weakfish fishing seasons, one order of magnitude lower than the current total fishing effort. The drastic reduction of total fishing effort estimated in this study is largely due to weak protection measures since the gillnet fisheries became the major conservation concern for franciscana by the end of 1970s in southern Brazil. Although the implementation of the proposed exclusion zones and limiting fishing effort will strongly impact the status quo, they were based on the best scientific evidence and on a clearly defined management goal to reduce the risk of the franciscana population's collapse in southern Brazil.