Updated standardized CPUE, size and spatial distribution of blue shark (Prionace glauca) caught by the Chinese Taipei longline fishery in the Atlantic ocean

The blue shark Prionace glauca catch and effort data from observers’ records of Chinese Taipei large longline fishing vessels operating in the Atlantic Ocean from 2007-2022 were analyzed. To cope with the large percentage of zero shark catch, the catch per unit effort (CPUE) of blue sharks, as the number of fish caught per 1,000 hooks, was standardized using a two-step deltalognormal approach that treats the proportion of positive sets and the CPUE of positive catches separately. Standardized indices with 95% bootstrapping confidence intervals are reported. The standardized CPUE of blue sharks in the North Atlantic had a lowest value in 2015, peaked in 2016, and decreased thereafter. The standardized CPUE of blue sharks in the South Atlantic was relatively stable from 2007-2019 but peaked in 2020 and decreased thereafter. The mean sizes of females were significantly smaller than those of males (P < 0.05) in the North and South Atlantic Ocean. The mean sizes of both sexes in the tropical waters were larger than those in the temporate waters.