Combined indices of abundance of blue sharks in the north and south Atlantic ocean

Indices of relative abundance (CPUEs) available for the stock assessments of blue shark (Prionace glauca) in the North Atlantic and South Atlantic Ocean were combined using different methods. Following the work conducted for the 2008 SCRS blue shark stock assessment, indices were combined through a GLM with two choices of weighting: by the catch of the flag represented by each index and by the area of the flag represented by each index. Additionally, a hierarchical index of abundance that combines all available indices into a single series was also developed. The three indices obtained for the North Atlantic and South Atlantic generally followed very similar trends, with a flat tendency in the North Atlantic and an increasing trend in the South Atlantic. These indices can potentially be used in sensitivity analyses in the stock assessments.