Interannual trends in the abundance and biomass of the autumn and winter-spring cohorts defined by two cohort separating methods using Japanese driftnet survey data

In this study, using driftnet survey data, we investigate the interannual trends in the abundance, biomass, and abundance-based CPUE of the two cohorts separating using two methods: separating them by the 170˚E line and by size. Similar trends in abundance, biomass, and abundance-based CPUE were observed for the winter-spring cohort using the two cohort-separating methods. However, for the autumn cohort, there were large differences in abundance and abundance-based CPUE between the two cohort-separating methods in some years due mainly to the high abundance of smaller squid (<30 cm) sampled in the area east of the 170°E line. While the overall interannual trends in the biomass were similar for both cohorts between the two cohort-separating methods, information on the size of squid caught by the commercial jigging fishery should be confirmed for cohort-specific stock assessments.