Results from the random longline survey 2024 in the Heard Island and McDonald Islands (HIMI) Patagonian toothfish fishery

In 2024, Australia conducted a trial for structured fishing with a ‘Random Longline Survey’ (RLS) to conduct longline research hauls that could be used for the development of a time series of fishery-independent longline hauls and lead to the estimation of an unbiased tag-based abundance index for the stock assessment. The execution of the 2024 RLS trial was successful in that it resulted in the target number of 119 research hauls, above-target number of hooks and a total of 137 recaptures. The lack of consistent biomass estimates and rather large confidence intervals from Chapman tag-release estimates indicated that a substantially larger sample size would be needed to achieve the intent of the trial to achieve a consistent and reliable biomass estimate. Nevertheless, Chapman biomass estimates for the 2024 season, based on commercial hauls only and based on research hauls only, were overall substantially higher than those estimated for the 2021 to 2023 seasons. This would indicate that tagging data from commercial hauls provided a more representative sample of the population in 2024 than in previous seasons.