Joint CPUE standardization of the Pacific saury in the Northwest Pacific Ocean by using the spatio-temporal modelling approach

Reliable indices of population abundance are essential for stock assessment. This study had two main objectives: (1) to evaluate the feasibility of using the R package sdmTMB as an alternative to the VAST model for CPUE standardization of Pacific saury, and (2) to update the joint CPUE index through 2024 using sdmTMB. The comparison using data through 2023 showed that sdmTMB produced results consistent with previous VAST assessments, while offering greater transparency and reproducibility. The updated standardized CPUE index indicated pronounced fluctuations over time, lower levels in recent years compared to the mid-1990s, and a slight increase in 2023 - 2024. Overall, sdmTMB provides a reliable framework for CPUE standardization and contributes to the stock assessment of Pacific saury.