Standardized catch rates in biomass for the blue shark (Prionace glauca) caught by the spanish surface longline fleet in the Indian Ocean during the 2001-2015 period

Abstract

Based on 2,049 trips by vessels in the Spanish surface longline fleet in the Indian Ocean during the period 2001-2015, standardised CPUE catch rates were obtained for the blue shark (Prionace glauca) using General Linear Modelling. The main factors considered were year, quarter, area, ratio, gear and the interaction quarter*area. The basic significant model obtained explained 81% of CPUE variability observed and suggests a stable trend for this blue shark stock in the Indian Ocean. Most of the variability in CPUE was explained by the targeting factor, as represented by the ratio between catch levels for the two most valued and prevalent species landed: swordfish and blue shark. Other significant factors were identified but these were less important. The MIXED model used to analyse sensitivity showed the same trend as that obtained using the basic case