Spatial predictions of blue shark catch per unit of effort (CPUE) and catch probability of juveniles in the southwestern Atlantic Ocean

In the present study, a General Regression Analysis and Spatial Prediction (GRASP) was applied to CPUE data of blue sharks to examine their distribution and abundance in relation to environmental factors in the Southwestern Atlantic Ocean.  CPUE was generated by blue sharks caught by the Brazilian pelagic longline fleet between 1997 and 2008.  In addition, size distribution of blue sharks caught in the pelagic longline fleet of Brazil was used to model the proportion of juvenile blue sharks in the catches between 2006 and 2008. Sea surface temperature was the most important environmental factor to influence the blue shark CPUE in the southwest Atlantic Ocean. CPUE spatial predictions indicated two separate areas of higher catch probabilities. Sea surface temperature was also the most important factor influencing juvenile blue shark spatial distribution. The spatial prediction map showed that juveniles were more frequent to the south of 35^oS and that the proportion of juveniles also was high in the area close to the mouth of the Plata River (Rio da Plata). However, for the majority of the Brazilian coast, between 5^oN to 30^oS, the proportion of juvenile blue sharks in the catch was very low compared with the catch from >35^oS.