Preliminary application of the stochastic surplus production model in continuous time (SPiCT) to neon flying squid in the North Pacific

This report represents the first attempt to apply the stochastic surplus production model in continuous time (SPiCT) to the autumn and winter-spring cohorts of neon flying squid in the North Pacific. We used NPFC statistics, which include annual catch and effort of neon flying squid fisheries in the North Pacific between 1995 and 2023. Catch per unit effort (CPUE) standardized with a generalized linear mixed model including year and NPFC member was used as a biomass index. We found that the relationship between biomass index and effort is not represented by a negative slope in both NFS cohorts, contrary to the assumption of surplus production model. Possibly due to the presence of some problems with the input data, results from the autumn cohort assessment using SPiCT were unacceptable, with wide confidence interval of estimates, such as relative biomass and fishing mortality. In the winter-spring cohort model, the estimated values appeared acceptable as the model diagnostics were satisfactory with consistent retrospective patterns for both relative biomass and fishing mortality. For future stock assessments of neon flying squid by the SSC NFS, we emphasize the importance of input data preparation and the estimation of biomass indices.