This paper presents further progress towards a two-area stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the Amundsen Sea region, defined here as SSRUs 88.2C–H. The region is split into two main areas: the North (SSRU 88.2H) comprising large mature fish, and the South (SSRUs 88.2C–G) comprising a mix of large mature fish and small immature fish.
Two-area stock assessment models were first developed for the region in 2014 and refined in 2015. Results showed the need to collect mark-recapture data in the South to help inform the estimation of biomass in the South. We present an update on these two-area stock models, which include two years of new data collected under a research plan. The assessment models were fit to the proportions-at-age in the catch and the mark-recapture data from the two areas. The results suggest that the research plan is successful in starting to inform the model, and in particular the size of the fish population in the South. We recommend that the current research plan be extended for a further 2-year period so that additional mark-recapture data can be collected particularly from the South, and that the models be developed further in the interim period. We also recommend that all Members, where possible, contribute to the development of annual age-length keys, using agreed otolith reading protocols and aging validation.