Standardized abundance index for recruitment of chub mackerel from Northwest Pacific summer surveys up to 2026

We conducted CPUE standardization for summer surface-trawl surveys for Pacific chub mackerel using the Vector Autoregressive Spatio-Temporal (VAST) model. We estimated local densities of young-of-the-year fish in the Northwest Pacific from 2002 to 2026 while accounting for sea surface temperature (SST) and temperature at 50 m depth, and spatial autocorrelation. The analysis showed high recruitment index values have occurred frequently since 2013, although the recruitment has declined since 2021. In 2026, the nominal and standardized indices decreased to 1% and 4% of their respective 2025 values, representing the lowest levels since 2012. Model diagnostics found no serious problems in residual patterns. We propose using this standardized recruitment index as an abundance index for age 0 fish in the Technical Working Group on the Chub Mackerel Stock Assessment (TWG CMSA).