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Proyecto H.1.b - Improve the yellowfin tuna stock assessment

01 ene. 2018 - 31 dic. 2020

Improve the yellowfin tuna stock assessment by exploring the use of an age-structured length-based catch-at-age statistical model with a monthly time step
  • The assessment of yellowfin is conducted every year, using Stock Synthesis
  • There are inconsistencies between the indices based on CPUE for longline and purse-seine sets on dolphins
  • Management quantities are sensitive to the longline CPUE data
  • The current assessment is no longer considered reliable for management advice and stock status indicators are used instead
  • Recent advances in stock assessment modelling allow several important improvements of the assessment model, with regard to a spatial stock assessment model, growth curves, time-varying selectivity, recruitment assumptions, data weighting, and diagnostics
  • A benchmark assessment is scheduled for 2020
Importancia para la ordenación
  • The stock assessment is used to provide management advice
  • The duration of recommended seasonal closures is based on the multipliers of fishing mortality (F) estimated in the bigeye and yellowfin assessments
  • Improvements in the yellowfin assessment will make the staff’s management advice more accurate and precise
Plan de trabajo y estatus
  • 2019: Explore different hypotheses to explain the difference between the indices of abundance, improve estimates of growth, re-evaluate the natural mortality assumptions, apply data weighting, conduct diagnostic tests
  • 2019: Workshop to finalize improvements to the longline CPUE and length-composition data (Project H.1.e)
  • 2020: Re-evaluate the model assumptions
  • Report(s) to SAC in 2019
  • Report to SAC in 2020
Fecha de actualización: 01 abr. 2021
Resumen de los avances en el periodo del informe
  • Most of the research and analyses to improve the bigeye stock assessment (Project H.1.a) is also applicable to yellowfin.
  • Several workshops were conducted that highlighted other areas where the stock assessment of yellowfin could be improved
    • February 2018: CAPAM workshop on the development of spatio-temporal models of fishery catch-per-unit-effort data to derive indices of relative abundance.
    • October 2018: CAPAM workshop on the development of spatial stock assessment models.
    • January 2019: workshop to evaluate bigeye and yellowfin tuna ageing methodologies and growth models in the Pacific Ocean.
    • February 2019: workshop to improve the longline indices of abundance of bigeye and yellowfin tunas in the EPO.
  • December 2019: An external review of the assessment of yellowfin tuna was held
  • May 2020: Benchmark assessment of yellowfin tuna
  • November 2021: IATTC-95-05 B. Yellowfin tuna (pag.50)
Retos y principales lecciones aprendidas
  • Management quantities are sensitive to the longline index, and the research had to be refocused to address several issues identified with the assessment
  • Lessons learnt from work on the bigeye assessment are applicable to yellowfin
  • An additional workshop to finalize the work on improving the longline CPUE and length-composition data was needed (Project H.1.e), but was not funded. Thanks to the collaboration of Japan and Korea, the work was advanced and indices from longline data were obtained
  • The standardized indices by size class from purse-seine and longline data where still incompatible pointing towards spatial differences in abundance trends of the northwest area (purse-seine index) and the southeast area (longline index), consistent with the a more complex stock structure, than the high-mixing hypothesis.
  • The benchmark assessment was done by modelling several hypotheses, resulting in a reference set of 48 models.
  • Time and data constraints limited the stock structure scenarios that could be included in the risk analysis
  • SAC-10 INF-F Evaluating inconsistencies in the yellowfin abundance indices
  • Xu et al., Fisheries Research 213
  • External review report
  • External review presentations
  • SAC-11-07 Benchmark assessment of yellowfin tuna
  • IATTC-95-05 B. Yellowfin tuna (pag.50)
The workplan for improving the bigeye assessment was changed in 2019 to encompass both bigeye and yellowfin tuna