Year-1 findings for preliminary stock assessment of Antarctic toothfish (Dissostichus mawsoni) in Subarea 88.3

This report compiles catch and biological data for Antarctic toothfish in CCAMLR Subarea 88.3 to provide a Year 1 baseline of population structure and key parameters. The analysis draws on observer samples and otolith ages from research blocks 883_1 to 883_12 collected from 2016 to 2025, with fishing and sampling conducted from January to April. Pooled length frequencies showed a clear bimodality near 60 to 70 cm and 130 to 160 cm. Application of an age length key confirmed the expected increase of age with length and produced age compositions that broadly correspond to the length results, typically with a single mode around 6 to 10 years and contributions from older ages. Sex-specific length-weight fits indicated females were heavier than males at the same length. Histology based maturity ogives yielded L50 of 108.5 cm for males and 115.4 cm for females and A50 of 10.2 years for males and 10.4 years for females. A tagging programme recorded 4,052 releases and 52 recaptures for a cumulative recapture rate of 1.28%. Among these recaptures, 33 (63%) occurred within Subarea 88.3, 12 (23%) in Subarea 88.1, and 7 (13%) in Subarea 88.2, indicating dominant residency in 88.3 with limited but detectable connectivity to adjacent subareas. Most fish remained within the release Subarea, while a smaller proportion moved eastward toward 88.1 and northward toward 88.2, suggesting limited but detectable connectivity among subareas. Key limitations were sparse coverage at the largest sizes and oldest ages, and recaptures were rare. These Year 1 products provide biological inputs and data standards for subsequent stages in which a standardised abundance index will be developed and tag based and survey style indicators will be added as set out in the staged plan.