1. Home
  2. Research
  3. Projects
  4. Revise trend estimation methods for purse-seine silky shark indices for the EPO
Project H.5.a - Revise trend estimation methods for purse-seine silky shark indices for the EPO

15 Sep 2018 - 15 May 2019

Program(s) in charge: Stock Assessment Program
Develop new methods to estimate trends in relative abundance of silky sharks from purse-seine observer data that are less influenced by inter-annual variability in oceanographic conditions
  • Fluctuations in the index of relative abundance for juvenile silky sharks correlate with inter-annual variability in oceanographic conditions in the offshore area of the northern EPO.
  • Recent fluctuations in the index are not biologically realistic, compromising the reliability of the index as a stock status indicator.
  • The index based on purse-seine observer data is the only index available for management because of data deficiencies in other fisheries.
  • New methods are necessary to estimate more reliable trends in relative abundance for the silky shark using purse-seine observer data.
Relevance for management
Improving the reliability of the purse-seine index will improve management advice for the silky shark in the EPO.
9 months
Workplan and status
  • Months 1-6: develop new methods for catch-per-set standardization.
  • Months 7-9: apply new methods to estimate a revised index.
Presentation for SAC-10, May 2019
Updated date: 01 May 2019
Progress summary for the reporting period
  • Pacific-wide analysis of environmental effects on silky shark indices finalized.
  • Current options for revising the silky shark indices evaluated.
Challenges and key lessons learnt
  • A recent Pacific-wide silky shark assessment was unable to fit to EPO and western Pacific indices simultaneously, even though movement was considered, which may indicate a lack of movement or assessment model mis-specification; tagging data were not available to be included in the assessment model.
  • Absent better information on specific environmental processes affecting silky shark distribution and movement, current options for revising the indices are problematic and may lead to additional bias.
  • A Pacific-wide tagging project, in collaboration with EPO coastal nations and the WCPFC, would produce invaluable information on movement and stock structure with which to improve indices.
  • SAC-10-17 Purse-seine indicators for silky sharks in the EPO
  • Lennert-Cody, et al. Fisheries Oceanography 28.
  • Clarke, S.C., et al., WCPFC Scientific Committee, August 2018.
  • Invited presentation, Institute of Statistical Mathematics, Tokyo, Japan, March 2019.