Evaluate best handling practices for maximizing post-release survival of silky sharks in longline fisheries, and identification of silky shark pupping areas for bycatch mitigation

Project M.2.b - Evaluate best handling practices for maximizing post-release survival of silky sharks in longline fisheries, and identification of silky shark pupping areas for bycatch mitigation

01 Jan 2018 - 31 Dec 2020

Program(s) in charge: Life History and Behavior Group

Funded

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Theme 4. Ecological impacts of fishing: assessment and mitigation
Goal M. Mitigate the ecological impacts of tuna fisheries
Target M.2. In collaboration with the industry, conduct scientific experiments to develop best practices for the release of prioritized bycatch species

Objectives

Estimate post-release survival of silky sharks captured by Mexican longline vessels in the eastern tropical Pacific, utilizing a best handling practice, and define boundaries encompassing the probable distribution silky shark pupping areas in the EPO

Background

Apparent severe decline in the population of silky sharks in the EPO, based on trends in standardized catch-per-unit-of-effort indices
Domestic longline fleets from Latin America conduct multi-species fisheries including retaining silky sharks
Defining the probable distribution of silky shark pupping areas would be useful for better understanding population structure and for consideration of conservation measures including spatiotemporal closures

Relevance for management

Resolution C-16-06 on conservation measures for silky sharks stipulates to improve handling practices for live sharks to maximize post-release survival, and identification of pupping areas of the silky shark

Duration

2018-2020

Workplan and status

2018-2019: 69 silky sharks will be tagged with archival tags on Mexican longline vessels, using best handling practices
2019-2020: The data obtained will be analyzed for post-release survival and movements during 2019 and 2020.
2019-2020: Exploratory analyses of silky shark size at capture data, compiled from various fisheries in the EPO, will be conducted to determine the areas and times where silky shark pupping most likely occurs

External collaborators

INAPESCA, Mexico

Deliverables

Silky shark post-release survival rate captured by Mexican longline vessels, using best handling practices
Probable distribution of silky shark pupping areas

Updated date: 01 Feb 2022

Progress summary for the reporting period

57 silky sharks were tagged with archival tags on Mexican longline vessels, using best handling practices
The satellite data sets obtained have been compiled
A table of metadata has been compiled, including release and pop-up dates and locations for all tags reporting to date, along with the fate of each shark.

Schaefer, K., Fuller, D., Castillo-Geniz, J.L., Godinez-Padilla, C.J., Dreyfus, M. and Aires-da-Silva, A., 2021. Post-release survival of silky sharks (Carcharhinus falciformis) following capture by Mexican flag longline fishing vessels in the northeastern Pacific Ocean. Fisheries Research, 234, p.105779.