Updated standardized CPUE of blue shark by Taiwanese large-scale tuna longline fishery in the Indian Ocean

The blue shark catch and effort data from observers’ records of Taiwanese large longline fishing vessels operating in the Indian Ocean from 2004-2017 were analyzed. Based on the nominal catch per unit effort (CPUE) distribution of the blue shark, four areas, namely, A (north of 10ºS, east to 70ºE), B (north of 10ºS, 70ºE-120ºE), C (south of 10ºS, 20ºE-60ºE), D (south of 10ºS, 60ºE-120ºE) were categorized. To cope with the large percentage of zero shark catch, the CPUE of blue shark, as the number of fish caught per 1,000 hooks, was standardized using a zero inflated negative binomial model. In general, the standardized CPUE series of the blue sharks caught by Taiwanese large-scale longline fishery showed a stable increasing trend (Figure 4). This sable trend suggested that the blue shark stock in the Indian Ocean seems at the level of optimum utilization during the period of 2004-2017. In this report, environmental effects were not included in the model for standardization. The results obtained in this study can be improved if longer time series of observers' data are available and environmental factors were included in the model.