Stock assessment based on age-structured assessment program for Chub mackerel in the North Pacific Ocean 2024

Based on the latest aggregated dataset and the agreed scenarios for Chub mackerel Scomber Japonicus in the North Pacific Ocean, this document conducted stock assessment used the Age-Structured Assessment Program (ASAP). Total 12 scenarios were run in ASAP, including two base cases of different natural mortality and other 10 sensitivity cases considering various CPUE, maturity and catch-at-age data.  The results indicated that there is no significant difference of biomass, SSB and fishing mortality estimates among all scenarios. The trend of SSB was similar with results from SAM, which was high before 1980, decreased to much low value between 1980 and 2020, recovered and kept at high values in the recent decade. No significant retrospective pattern present for the two base cases, with Mohn’s ρ values of B, SSB and F in the range of -0.16~0.19. Preliminary projections were also conducted, providing estimates of biomass, catch and SSB in next ten years under different F and TAC. Even ASAP was not selected as the benchmark stock assessment model, results of which could also provide some valuable information to scientists and mangers for comparison and reference.