Preliminary tag-recapture based population assessment of Antarctic toothfish (Dissostichus mawsoni) in Subarea 48.4 - 2024/25 fishing season

The local biomass of Antarctic toothfish (Dissostichus mawsoni) in CCAMLR Subarea 48.4 is estimated from tagging returns, giving a five-year average of 968 tonnes since 2020. Applying the CCAMLR agreed precautionary assumption of setting harvest rates based on a 5-year average biomass, and harvest rate of γ = 0.038, results in a 2025 catch limit of 37 tonnes.

Historically, a precautionary approach has been applied in treating the 48.4 Antarctic toothfish as a separate stock. Based on the biological characteristics of the catches in Subarea 48.4, and the surrounding regions, the Antarctic toothfish around the south of Subarea 48.4 are now hypothesised as being part of a much larger stock that extends south into Subareas 48.2, 48.6 and possibly 48.5. The current method of assessment, based on tag returns, consequently, is considered to provide an estimate of the local biomass. There is initial evidence indicating a northward shift of the boundary between Antarctic and Patagonian toothfish species in Subarea 48.4. Further observations and analyses are required to monitor any changes in stock area due to climate change and / or stock dynamics, and ensure any changes are integrated into the fisheries management of this area.