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Project H.4.a - Conduct regular stock assessments of tropical tunas
Ongoing
Program(s) in charge: Stock Assessment Program
Funded
Objectives
Update the assessments of bigeye, yellowfin, and skipjack tunas
Background
  • Assessments of bigeye, yellowfin, and skipjack are conducted every year
  • Bigeye and yellowfin assessments use the Stock Synthesis modeling platform
  • Skipjack assessment is based on stock status indicators
  • Assessments are updated annually, using the most recent data
  • Major improvements to the assessments (methods and assumptions) are implemented periodically
Relevance for management
  • The staff’s management advice for tunas is based on its stock assessments
  • The duration of the seasonal closures recommended by the staff for bigeye and yellowfin are based on the F multipliers estimated in the assessments
Duration
Every year (March-May)
Workplan and status
  • 15 March: data for previous year available; assessments initiated
  • Three weeks before SAC meeting: Assessment reports posted on IATTC website
  • Mid-May: Present assessments at SAC meeting
Deliverables
Stock assessment reports for the SAC and the IATTC; presentations at SAC and IATTC meetings
Updated date: 01 Mar 2024
Progress summary for the reporting period
  • Benchmark assessment conducted for bigeye 2020
  • Benchmark assessment conducted for yellowfin 2020
  • Interim assessment conducted for skipjack 2022
  • Indicators constructed for the three species 2023
  • External review of modelling aspects for stock assessments of tropical tuna in the eastern Pacific Ocean (Nov 06-10, 2023) RVMTT-01
  • External review of data used in stock assessments of tropical tuna in the eastern Pacific Ocean (Oct 02-06, 2023) RVDTT-01
  • Benchmark assessment for bigeye 2024
  • Benchmark assessment for yellowfin tuna 2024
  • Benchmark assessment for skipjack tuna 2024
Challenges and key lessons learnt
The results of the bigeye and yellowfin assessments were considered unreliable, and they were improved for the 2020 benchmark assessments (Projects H.1.a and H.1.b). The models were further improved to address the uncertainty about the stock structure of yellowfin tuna and the bimodal pattern in the results of the risk analysis for bigeye tuna. The external review panels suggested several scenarios to include in the risk analyses for both species.
  • SAC-11-06 Bigeye tuna: benchmark assessment
  • SAC-11-07 Yellowfin tuna: benchmark assessment
  • SAC-12-06 Assessment methods for skipjack in the EPO: a proposal relying on recent data from the IATTC regional tuna tagging program (2019-2022)
  • SAC-13-07 Skipjack tuna: interim assessment
  • SAC-14-04 Stock status indicators (SSIs) for tropical tunas in the eastern Pacific Ocean
  • RVMTT-01-REP External review of modelling aspects for stock assessments of tropical tuna in the eastern Pacific Ocean (Nov 06-10, 2023)
  • RVDTT-01-REP External review of data used in stock assessments of tropical tuna in the eastern Pacific Ocean (Oct-02-06, 2023)
  • SAC-15 INF-F - Stock status indicators (SSIs) for tropical tunas in the eastern Pacific Ocean
Comments
A new scientist was hired to join the stock assessment team who will lead the skipjack stock assessment.