- Objectives
- Construct indices of relative abundance and length compositions from longline data for yellowfin and bigeye, ideally using spatiotemporal models
- Background
- Indices of relative abundance derived for longline CPUE data are the most important piece of information in the bigeye and yellowfin stock assessments
- Only Japanese data are currently used to create these indices
- A workshop was held in February 2019 to understand the data from other CPCs that could be used to improve the indices of abundance (WSLL-01)
- Preliminary results on constructing indices on combined data were obtained during the workshop
- The resulting indices are needed for the benchmark assessments of bigeye and yellowfin scheduled for 2020
- Relevance for management
- The indices have a direct impact on the stock assessment, and any improvements in the indices will directly improve management advice for bigeye and yellowfin
- Duration
- 18 months
- Workplan and status
- Jun-Sep 2019: Preparatory work depending on the availability of operational level data
- Oct-Dec 2019: Collaborative work and workshop
- Jan- May 2019: Preparation of documents
- External collaborators
- Scientists from Japan, Korea, Chinese Taipei, China
- Invited researchers
- Deliverables
- Indices of relative abundance
- SAC documents
- Updated date: 01 Apr 0201
- Progress summary for the reporting period
- This project was not funded but some activities took place:
- Japanese (Dr. Keisuke Satoh) and Korean (Dr. Sung-Il Lee) scientists visited the IATTC for a second tome to continue the collaborative work
- The longline indices of abundance by size class for bigeye and yellowfin tuna were obtained using spatiotemporal models. The indices were used in the benchmark assessment for bigeye tuna (SAC-11-06), in models for yellowfin tuna done in preparation for the external review of the yellowfin tuna assessment, and as indicators for both species (SAC-11-05)
- One manuscript was prepared and submitted for publication in a peer-review journal
- Challenges and key lessons learnt
- The operational data essential for improving the assessment are not permanently available to the staff.
- Matching size-composition and operational data for Japan proved difficult, and is not yet completed, the indices were obtained by modelling data aggregated into a 1° latitude by 1° longitude
- Adding the data for Korea to the standardized indices proved difficult for two reasons:
- the comparison with the Japanese data could not be done as operational data was only available to the staff when the scientists were present, and the visits took place in different times,
- the aggregated data indicated that the two fleets may have different size distributions, but this differences may be due to changes in the sampling protocol (Japan changed from fishermen sampling to observer sampling after 2011, and after 2014 all measurement were taken by observers, Korean data include both fishermen and observer sampling, after 2013 a larger proportion of the data comes from observers), or small sample size (the observer coverage is less than 5%).
- SAC-11-06 Benchmark assessment for bigeye tuna
- External review of the yellowfin tuna assessment
- SAC-11-05 Indices used as indicators for yellowfin and bigeye tuna
- Satoh et al, manuscript submitted
- Comments
- Peer review papers resulting from the collaborative work are in preparation
