Revised Standardized Abundance Indices for Ages 0 and 1 Fish of Chub Mackerel from Northwest Pacific Autumn Surveys up to 2023

We conducted CPUE standardization of surface trawl surveys in autumn for Pacific chub mackerel using the Vector Autoregressive Spatio-Temporal (VAST) model. We estimated local densities of 0-year-old fish and 1-year-old fish in the Northwest Pacific from 2005 to 2023 with consideration for environmental factors of sea surface temperature (SST) and 30m-depth temperature as well as spatial autocorrelation. We slightly revised model configurations on the 1-year-old fish analysis following a suggestion from the Technical Working Group for the Chub Mackerel Stock Assessment (TWG CMSA), but results little changed. The analysis showed high levels of abundances frequently occurred since 2013. Model diagnostics found no serious problems in residual patterns. We propose the standardized indices to be utilized as the abundance indices of age-0-fish and age-1-fish in the TWG CMSA.