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- Objectives
- Conduct a post release survival study (PRS) of silky sharks captured in class 2-5 purse seine vessels to generate quantitative estimates of survival and to identify best handling and release methods
- Background
- Understanding and reducing the impacts of tuna fishing on associated species is a requirement of the Antigua Convention.
- Improving the post release fate of prioritized, vulnerable and/or no retention species is a research priority to promote sustainable fisheries.
- Vessel operational characteristics and handling and release practices have been shown to have significant impacts on survival outcomes for discarded species, including sharks.
- PRS rates of incidental sharks in smaller size class purse seine vessels
- is an existing knowledge and data gap. Therefore, a satellite telemetry and blood chemistry study will be conducted in collaboration with TunaCons observers on class 2 – 5 vessels.
- Relevance for management
- Results will improve stock and vulnerability assessments assumptions and help design the best handling and release practices for this fleet segment
- Duration
- 36 months
- Workplan and status
- Year 1: Purchase tagging and blood chemistry material. Train observers in tagging and blood withdrawal techniques. Develop forms and data collection methods to record additional data on handling release methods used and condition of the animal.
- Year 2: Only half of the funds are dispersed per year so year two will be focused on deploying the second batch of tags and continued blood sampling of shark bycatch
- Year 3: Data analysis and write-up of results.
- External collaborators
- CPCs, Tuna Cons, MSC
- Deliverables
- Shark PRS estimates by landing stage and handling and release method for smaller size class purse seine vessels.
- Improvements to best handling and release practice guidance for this sector as well as improved assumptions for parameters in the species assessments.
- Reports and presentations for the EBWG and the SAC, including main results and recommendations of the project
- Updated date: 01 May 2024
- Progress summary for the reporting period
- In July 2023 IATTC staff travelled to Manta to train IATTC and TUNACONS observers to tag and to conduct blood withdrawals on incidentally captured sharks to generate survival estimates for silky sharks across sizes ranges captured in small purse seines (i.e., class 2-5). During Year 1 of the study 5 trips were conducted, where 21 tags were deployed on sharks and blood lactate levels were measured for survival estimation, by landing stage, release condition and handling method.
- Challenges and key lessons learnt
- There appears to be another bug in the tagware that is proving problematic in that some data is not transmitted and tags are shed early. Fate on tag shedding has been established however and may still prove useful. The training has proven effective, and the data being generated for this study is of very high quality for survival rate projections for this fleet.
- Comments
- During year 2 an additional 16 tags are set to be deployed during 3-4 cruises.