22nd Regular Session of the Scientific Committee

Review of the 2026 yellowfin tuna stock assessment

SC22 will review the results of the 2026 yellowfin tuna stock assessment, including data inputs, CPUE analysis, stepwise (bridging) analyses, and methodology, and will consider new findings, suggestions, and future research needs, including budget implications, to provide management recommendations to the Commission. 

• The last yellowfin tuna stock assessment was conducted in 2023 and reviewed at SC19. The 2023 yellowfin tuna stock assessment concluded that the stock is not experiencing overfishing (100% probability Frecent<FMSY) and is not in an overfished condition (0% probability SBrecent/SBF=0<LRP). SC19 identified priority areas for the next assessment, including improving CPUE standardisation through clearer representation of model effects and inclusion of key covariates affecting catchability, such as hooks, vessel characteristics, and fishing practices, as well as explicit consideration of effort creep and temporal changes in catchability. Further work was also requested to better evaluate environmental and region-specific covariates and their influence on both abundance and catchability. 

  SC19 called for the development of alternative CPUE series under different model assumptions to better represent uncertainty and to examine implications for regional scaling, alongside evaluation of alternative spatial structures, including single-region areas-as-fleets or equatorial-focused models. Strengthened characterisation of uncertainty was also requested through expanded sensitivity analyses, refinement of uncertainty grids, and assessment of parameter sensitivity to initial conditions. 

  Further work was requested on key biological processes, including natural mortality and growth, and on resolving conflicts in size and weight composition data. SC19 also emphasised improved use of tagging data, including alternative modelling approaches and stand-alone (external) tag-based models, and highlighted the need for improved catch estimates and biological sampling, particularly for Indonesia, the Philippines, and Vietnam. In addition, SC19 encouraged simplification of model structure, improved model stability and convergence, exploration of alternative assessment platforms, clearer reporting of model assumptions, and provision of stochastic projections to support a more robust and transparent assessment.