Characterisation of the fisheries catching silky sharks (Carcharhinus falciformis) in the Western and Central Pacific Ocean

Citation

Brouwer, S., Large, K., & Neubauer, P. (2023). Characterisation of the fisheries catching silky sharks (Carcharhinus falciformis) in the Western and Central Pacific Ocean. WCPFC-SC19-2023/SA-IP-09. Report to the Western and Central Pacific Fisheries Commission Scientific Committee. Nineteenth Regular Session, 16–24 August 2023.

Summary

The next stock assessment for silky shark (Carcharhinus falciformis) is scheduled for 2024. The work leading up to the assessment will be undertaken over two years. This paper, as well as Neubauer et al. (2023), represent the background work for the SC19s consideration and information for feedback into the SC20 assessment. Silky shark are caught as bycatch in longline fisheries targeting tuna, billfish and blue sharks between 10◦N and 20◦S, and as bycatch in the tropical purse seine fisheries of the WCPO. No target fisheries exist for silky sharks and since 1st July 2014 their retention has been prohibited within the WCPO. Since 2015, almost all silky sharks have been discarded or cut-free from longline sets and more than half of those are released alive and healthy. Similarly, in the purse seine fishery, all silky sharks have been released since 2015, but release condition is largely unknown.

This paper describes the longline gear designs that catch silky sharks; presents information on fate and condition; length data; raw CPUE information; and discusses the impact of vessel flag and observer program on the spatio-temporal distribution of the catch and provides recommendation for the 2024 stock assessment.

The following recommendations are proposed for the Scientific Committee to consider:

  • Observer programs and/or vessel flag be included along with gear characteristics as variables in CPUE and length analysis standardisation.

  • Incorporate post release survival of silky sharks into other analyses evaluating measures to reduce fishing-related mortality.

  • Noting that there are very few data for the release condition of silky sharks landed on purse seine vessels, it is recommended that observers on purse seine vessels be encouraged to collect data on shark release condition.

  • It is recommended that the 2024 stock assessment explicitly provide commentary on the recent trends in fishing mortality since the inception on CMM2019-04.