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- Improve the yellowfin tuna stock assessment:Explore alternative hypotheses of stock structure and life-history for YFT in exploratory stock assessment models
- Objectives
- Improve the yellowfin tuna stock assessment by exploring alternative hypotheses of stock structure and life-history
- Background
- A benchmark assessment was conducted in 2020 with 48 models representing several hypotheses for the stock. The main overarching hypotheses, stock structure, was not possible to address extensively
- Relevance for management
- The stock assessment is used to provide management advice
- The duration of recommended seasonal closures is based on risk analyses of bigeye and yellowfin that use the assessment results
- Improvements in the yellowfin assessment will make the staff’s management advice more accurate and precise
- Duration
- 2021-2024
- Workplan and status
- 2021: Re-evaluate the natural mortality assumptions
- 2022-23: Explore different hypotheses on stock structure
- 2022: Workshops to finalize improvements to the longline CPUE and length-composition data (Projects H.1.e – ext and H.1.f)
- 2023: Re-evaluate the model assumptions and implement exploratory models
- 2024: Benchmark assessment
- Deliverables
- Report(s) to SAC in 2022, 2023 and 2024
- Updated date: 01 May 2023
- Progress summary for the reporting period
- The conceptual model (CM) for yellowfin tuna in the EPO was updated based on extensive literature review. The CM relies strongly on environmental forcing. The work focused on exploratory analyses. Tree analysis on length composition data using environmental gradients as explanatory variables were done. The exploratory analyses will be the based for the new models that will be included in the risk assessment. An external review of the assessment for yellowfin tuna will be done during 2023.
- Challenges and key lessons learnt
- The workshop on longline CPUE and length-composition data did not take place for lack of funding, but discussion with CPC, mainly Japan and Spain, took place, facilitated by visits of one staff member to the Centro Español de Oceanografía (Madrid) and National Far-Sea lab (Yokohama) while on trips for other meetings. Collaborative work was agreed and a new MOU with Japan was discussed.
- The ideas related to this work were discussed in scientific meetings:
A SAC document was prepared
- Comments
- The staff will start collaborative work with Japan to analyze the logbook data, which will initiate after SAC-14 with a 2 month visit of a Japanese scientist.
