Preliminary standardized CPUE of blue shark in the Indonesian tuna longline fishery estimated from scientific observer data, for the period 2005-2014

The blue shark (Prionace glauca) is one of the dominant caught and most important bycatch shark species for Indonesian tuna longline fishery in the Indian Ocean. The number of Indonesian tuna longline fleets in Indian Ocean are 1,282 units. There are two types of tuna longline fleet in Indonesia, based on the product destinations, namely fresh and frozen tuna. This working document analyses the catch, effort, nominal and standardized CPUE trends for blue shark captured by this fishery, for the period between 2005-2014. Nominal annual CPUEs were calculated as number (N)/1000 hook. Standardized CPUEs were estimated with Generalized Linear Models (GLMs) using year, quarter, area, 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). Preliminary results showed the factors that contributed most for the deviance were the area, followed by year, quarter, number of ooks between floats (NHBF), and then the other effects and the interactions. The trends of the standardized CPUEs were relatively similar to the nominal series, but with smoother peaks. In general there were no noticeable trends, with the series varying along the period.