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This document presents an update of Management Procedure (MP) evaluation results for bigeye and yellowfin tunas since the 2019 IOTC Technical Committee on Management Procedures (TCMP) and Commission meetings, from which we highlight the following points:
• The reference set Operating Models (OMs) have evolved since the 2019 TCMP, with some minor corrections, and more thorough investigation of the yellowfin OM in particular. However, the changes do not substantially change the MP evaluation results reported to the 2019 TCMP.
• Substantial effort was spent developing the model-based MP algorithms, including i) improving the reliability of surplus production model fitting, and ii) developing a new class of MP (model-rebuilding class) which includes an internal projection algorithm that may improve rebuilding behaviour.
• Funding has been identified to continue the yellowfin and bigeye MSE work through 2020.
• Bigeye MP evaluation results:
o The 2019 TCMP requested results from 2 tuning objectives:
▪ B18.2: Pr(Kobe Green 2030-34) = 0.6 (stock status in the Kobe green quadrant over the period 2030-2034 exactly 60% of the time, averaged over all simulations)
▪ B18.3: Pr(Kobe Green 2030-34) = 0.7 (stock status in the Kobe green quadrant over the period 2030-2034 exactly 70% of the time, averaged over all simulations)
o Performance evaluations for contrasting MP classes are presented for the reference set OM and a suite of robustness tests.
o The MP results were largely unchanged from the 2019 TCMP.
o The generally optimistic stock status for bigeye results in the tendency for MPs to recommend catch increases which may not be consistent with recent industry objectives (i.e. otherwise current catches would be higher). If catches have to be greatly increased to hit the tuning objective, this can result in subsequent biomass declines to below target levels, but this is not a big problem with the current tuning levels.
o While no obvious problems were identified with the bigeye reference set OM, it will need to be compared with the results and insights from the 2019 stock assessment.
o The species-specific summaries in the text identify development feedback priorities required from the 2019 WPTT and WPM.
• Yellowfin MP evaluation Results
o The 2019 TCMP requested results from 2 tuning objectives:
▪ Y18.2: Pr(B(2029) > B(MSY)) = 0.5
▪ Y18.3: Pr(B(2034) > B(MSY)) = 0.6
o Results of contrasting MP classes are presented for the reference set OM and a suite of robustness tests. As per the 2019 TCMP request, key MP results are presented in additional formats that only summarize performance up to the tuning rebuilding targets. This request was motivated by the fact that the MPs available at the time had a tendency to overshoot the biomass rebuilding objective.
o The revised MPs largely resolve the biomass overshoot problem, and demonstrate the value of i) developing situation-specific MPs, rather than relying on generic MPs, and ii) having competing MP developers that explore different approaches and share experiences. However, the MP results are still very pessimistic in that large catch reductions from current levels are likely required to hit the rebuilding targets.
o The MPs that achieved successful tuning all required the TAC change constraints to be larger than the targeted 15% (>50%). As per the TCMP request to explicitly explore how change constraints relate to rebuilding possibilities, the earliest possibly recovery dates (i.e. based on continuous quota drops rather than feedback-based MPs) were determined for a range of options (with quotas effective starting 2021) including:
▪ 2042 with a 15% change constraint
▪ 2031 with a 25% change constraint
▪ 2029 with a 35% change constraint
▪ 2022 with a fishing moratorium
• There are substantial concerns about the most recent yellowfin stock assessment, and the corresponding operating models upon which the MP evaluations are undertaken. Accordingly, the OMs will need to be revisited in relation to the results and insights that may arise from the ongoing assessment review process.
