Based on the three-step sensitivity framework recommended by WG-SAM-2024 (para. 5.10), this paper presents an updated assessment for Patagonian toothfish (Dissostichus eleginoides) at Heard Island and McDonald Islands in Division 58.5.2. Starting with the 2023 assessment model that was used to provide management advice, this paper presents a bridging analysis and results from a variety of sensitivity analyses, many of which are related to the use and integration of tagging data. For the base-case model in step (i), the stock assessment model was updated with catch until the end of 2024 and observations until the end of 2023. This 2024 base-case model is highly consistent with the 2023 stock assessment model. There has been a significant amount of supplementary work that characterises key sources of uncertainty in the model and demonstrated that there is a downward bias in recent YCS and SSB estimates, and unreasonably high estimates of the survey catchability, from the base-case model. Steps (ii) and (iii) of the sensitivity framework have proven to be complex and require further work and considerations before the outcomes of these steps could reliably inform a management decision.
We consider that this assessment does not provide advice to supersede the current agreed advice to inform an updated recommendation by WG-FSA-2024 on catch limits for Patagonian toothfish in Division 58.5.2. We therefore recommend to roll over the current catch limit of 2660 t for one year to the 2024/25 fishing season, proceed with the workplan and present an updated stock assessment to WG-FSA-2025.
We consider that this approach is precautionary and has a low risk:
- There has been a significant amount of supplementary work that characterises key sources of uncertainty in the model and demonstrated that there is a downward bias in recent YCS and SSB estimates from the base-case model.
- Current estimates of recent YCS are likely to underestimate the potential contribution of these year classes to future spawning biomass, so any recovery towards the target may proceed faster than currently projected.