Updated and revised historical catch and standardized CPUE series of the blue shark by Taiwanese large-scale tuna longline fisheries in the North Pacific Ocean.

Abstract

In the present study, the blue shark catch and effort data from observers’ records of Taiwanese large longline fishing vessels operating in the North Pacific Ocean from 2004-2012 were analyzed. Due to the large percentage of zero shark catch, the catch per unit effort (CPUE) of blue shark, as the number of fish caught per 1,000 hooks, was standardized using delta lognormal approach. The analysis of standardized CPUE showed a stable increasing trend for blue sharks. The results suggested that the blue shark stock in the North Pacific Ocean seems at the level of optimum utilization. Estimated blue shark by-catch in weight ranged from 1 ton in 1973 to 1,357 tons in 2002. The results obtained in this study can be improved if longer time series observers' data are available.