Standardized CPUE of blue shark in Indonesian tuna longline fishery estimated from scientific observer data, for the period 2005 – 2016.

This working document analyses the catch, effort, nominal and standardized CPUE trends for blue shark captured by the Indonesian tuna longline fishery for the period 2005-2016. Nominal annual CPUEs were calculated as number (N)/1000 hooks and were estimated with Generalized Linear Models (GLM) and Generalized Linear Mixed Models (GLMM). Using year, quarter, area, the environment variables (sea surface temperature, chlorophyll-a concentration, eddy kinetic energy, sea level anomaly, and absolute dynamic topography) and Operational characteristics of the gear. Model Goodness-of-fit and model comparison was carried out with the Akaike Information Criteria (AIC) and the pseudo coefficient of determination (R2) and model validation with a residual analysis. The final estimated indexes of abundance were calculated by least square means (LSMeans) or Marginal Means. The results showed the factors that contributed most for the deviance were the Area, followed by Year, SST, NHBF and Quarter, followed by the other effects and the interactions. In general, there were no noticeable trends, with the series varying along the period. This paper presents the update of the index of abundance for the blue shark estimated from captures from the Indonesian pelagic longline fleet in the Eastern Indian Ocean and can be used in future stock assessments models.