Evaluating the impacts of environmental variables on spatial density distributions of Pacific saury by using spatio-temporal modelling

This study investigated the influence of environmental factors on Pacific saury distribution in the Northwestern Pacific Ocean using the spatiotemporal modeling framework sdmTMB. We analyzed the catch-per-unit-effort (CPUE) dataset compiled by North Pacific Fisheries Commission members and examined the variation of CPUE in related to multiple environmental variables through different functional relationships during 2001-2023 by using species distribution models. The quadratic function model provided the best fit, explaining 36.1% of variance. Results suggested that positive associations with net primary production and a dome-shaped response to sea surface salinity, peaking around 33 PSU. Spatial random effects showed distinct seasonal migration patterns, with distributions shifting from eastern offshore waters (160°-170°E) during May-July to coastal waters (40°-45°N) in August-September, followed by a southward coastal migration from October-December. In recent years (2021–2023), Pacific saury density has declined across the region, likely reflecting significant changes driven by environmental variations.This preliminary analysis provided insights how environmental factors and seasonal patterns influence Pacific saury habitats, with potential for model improvement through the exploration of additional environmental variables.