- Objectives
- Conduct an exploratory assessment for bigeye tuna in the Pacific Ocean
- Background
- The assessment for bigeye tuna in the EPO shows a regime shift in recruitment.
- Both conventional and archival tagging data suggest that juvenile bigeye tend to move from the WCPO to the EPO.
- Bigeye tuna in the EPO and WCPO have notably different growth curves.
- The exploratory Pacific-wide assessment for bigeye tuna can help test the hypothesis that the regime shift in the recruitment of EPO bigeye tuna is caused by ignoring the immigration of bigeye tuna from the WCPO.
- Relevance for management
- Improvements in the stock assessment will improve the management advice
- Duration
- 2 years
- Workplan and status
- Obtain data for bigeye tuna in the WCPO
- Build a single-area assessment model for bigeye tuna in the WCPO using Stock Synthesis
- Build a two-area Pacific-wide assessment model for bigeye tuna with assumed movement rates between WCPO and EPO
- Conduct the exploratory assessment and evaluate the sensitivity of the stock status of EPO bigeye to the assumed movement rates
- Report to SAC-13 in 2022
- External collaborators
- Scientists from the Pacific Community (SPC)
- Deliverables
- Report to SAC-13 in 2022
- Updated date: 01 May 2021
- Progress summary for the reporting period
- July 2020: Obtained the data needed to build a single-area assessment model for bigeye tuna in the WCPO using Stock Synthesis
- August 2020: Built a single-area assessment model for bigeye tuna in the WCPO using Stock Synthesis
- November 2020: Built a two-area Pacific-wide assessment model for bigeye tuna with assumed movement rates between WCPO and EPO
- Challenges and key lessons learnt
- Fitting selectivity curves to length compositions are more difficult in the Pacific-wide model where the population consists of two groups of bigeye tuna with notably different growth curves.
- Results are sensitive to the assumed movement rates between the WCPO and EPO while the values for Pacific bigeye, especially those for adult, are unknown.