Japanese survey biomass index of Pacific saury up to 2021 using VAST model

Vector Autoregressive Spatio-temporal (VAST) model was applied to Japanese fishery-independent survey data to predict Pacific saury distribution and estimate biomass index from 2003 to 2021 under an assumption that age-specific fish distribution pattern is consistent over the research period. The estimated biomass index from the selected VAST model with minimum AIC indicated similar year trends with the index from a design-based approach after 2010. The estimated biomass index dropped to the historical lowest in 2020 since 2003, though much more uncertain compared to other years, and remained at a low level in 2021.