Catch disposition of blue sharks (Prionace glauca) caught by longliners in the southwestern Atlantic

This study provides an overview of the catch disposition of blue sharks (Prionace glauca) caught by longliners over the Southwestern Atlantic Ocean and assess the relative magnitude of the non-retained catch. Data were gathered by scientific observers on board Uruguayan and Japanese flagged fishing vessels operating between 2009 and 2013. A total of 102 588 blue sharks were caught during the study period and catch disposition statistics (retained, discarded dead, released alive and lost) were assessed for each fishing fleet. Although results here presented should be considered preliminary, scientific observer data showed that the nonretained catch (not included in landing reports and logbooks) can be as high as 15% of total blue shark catch. Non-retained individuals were mainly comprised by smaller size classes than those typically retained. Most non-retained sharks were released alive, but because postcapture mortality is still little known for blue sharks some uncertainty remains regarding long term mortality. We suggest that these aspects should be considered in future evaluations as they may help improving fishing selectivity and mortality as well as relative abundance estimations.