Stock structure of Antarctic toothfish in Statistical Area 88 and implications for assessment and management

We review the stock structure of Antarctic toothfish in Statistical Area 88 with the aim of characterising the likely stock boundaries relative to stock assessments. We include information from genetic studies, otolith microchemistry, stable isotopes, tagging, size and age structure, growth dynamics, and egg and larval dispersal simulations. Taken together, the information suggests two biological stocks with limited mixing, especially at adult stages: a Ross Sea Region stock and an Amundsen Sea Region stock. The Amundsen Sea stock likely includes juveniles and adults along the continental margin in the Bellingshausen Sea (SSRUs 88.3A–D), SSRUs 88.2C–G, and a spawning region in the seamount complex of SSRU 88.2H. Key information needs to further understand stock structure include characterising the movement patterns and linkages of Antarctic toothfish in the 80–120 cm size range, throughout the continental margin SSRUs of the Amundsen Sea (i.e. SSRUs 88.2C–G). We recommend that the Ross Sea Region stock assessment boundaries remain as Subarea 88.1 plus SSRUs 88.2A–B and that the Amundsen Sea Region boundaries include SSRUs 88.2C–H.  Further research to better elucidate the proper stock affiliation of adjacent portions of the Bellingshausen Sea (SSRUs 88.3A-D) and juveniles in SSRUs 88.2C–G is a priority.