Small Working Group on New Stock Assessment Models for Pacific Saury – Progress Summary for 2025

The Small Working Group on New Stock Assessment Models (SWG NSAM) held three meetings in 2025 to advance the development of an age-structured Stock Synthesis 3 (SS3) assessment model for Pacific saury. Major progress included converting the model from an annual to a seasonal time step, incorporating updated fishery and survey data, and implementing time-varying growth, which improved fits to length composition, addressed earlier issues related to reductions in mean size, and partially reduced retrospective patterns, although some retrospective issues remain. However, important challenges persist, including limited prediction skill and substantial uncertainty in natural mortality and steepness. These uncertainties also hinder the reliable estimation of the yield curve and MSY-related reference points. As a result, the SWG was unable to finalize base and sensitivity cases in 2025. The group recommends continuing model development in 2026 and ensuring sustained technical support from external experts.