Special Session of the Scientific Committee: Full Annotated Agenda

Background:

SC22 recommended convening a two-day Special Session of the Scientific Committee, in hybrid format, adjacent to WCPFC23, to review and formally approve the revised bigeye tuna operating model (OM) reference set. BMW02 subsequently identified the remaining scientific work required to support the adoption of a bigeye management procedure (MP) at WCPFC23. SC22 also agreed to revisit the development of the Pacific bluefin tuna long-term harvest strategy at the Special SC Session, following discussions concerning the scientific evaluation and review of newly proposed harvest control rules (HCRs).

SSSC01 Action: 

The Special SC Session will be opened by the Chair, and participants will be invited to adopt the agenda and confirm the scope and expected outcomes of its deliberations. The Session will focus on completing the necessary scientific review of the bigeye MP framework and considering the outstanding PBF harvest strategy matters referred by SC22 (paragraph 471, SC22 Report), while distinguishing scientific recommendations from management decisions reserved for the Commission and its relevant subsidiary bodies.

Background:

SC22 acknowledged substantial progress in developing the bigeye operating model (OM) reference set based on the 2023 stock assessment but noted that, although consensus was not reached on acceptance of the 2026 stock assessment, its analyses indicated more depleted stock conditions and a greater risk of falling below the limit reference point (LRP) than represented in the existing OM grid. SC22 therefore requested the Scientific Services Provider (SSP) to expand the OM uncertainty range to cover plausible lower-depletion scenarios and recommended formal review and approval of the revised OM reference set at the Special SC Session. BMW02 welcomed the revised OM grid, noting its improved coverage of lower-depletion scenarios, including conditions below the LRP, and supported its use in further candidate MP evaluations, subject to technical review and formal approval by the Special SC Session.

 SSSC01 Action: 

SSSC01 will review the revised OM reference set, including its settings and coverage of plausible stock conditions informed by the 2026 stock assessment analyses. Attention should be given to the representation of lower-depletion scenarios and associated LRP risk, and any substantive differences from the previous OM set. SSSC01 may determine whether the revised OM reference set provides an appropriate scientific basis for evaluating candidate bigeye MPs, consider its formal approval, and identify any remaining uncertainties that may warrant subsequent robustness testing or consideration under the monitoring strategy.

Background:

SC22 reviewed the revised Stock Synthesis-based estimation method (EM) for the bigeye management strategy evaluation (MSE) and supported its use in principle, subject to further testing against the revised operating model (OM) reference set. Following SC22's request to expand the OM uncertainty range towards lower depletion levels, further evaluation of EM performance against the revised OMs was identified as necessary. BMW02 noted the ongoing work to evaluate the revised EM, with results to be considered by the Special SC Session. The robustness of the EM is important because its estimates of stock status provide inputs to the harvest control rules (HCRs) used to determine management outputs.

SSSC01 Action: 

Noting that the EM works in partnership with the HCR design to define appropriate MP outputs, SSSC01 will review the performance of the revised EM against the updated OM reference set, including convergence, estimation bias, precision and its ability to track changes in stock status, particularly under lower-depletion scenarios and near the limit reference point (LRP). SSSC01 may consider implications of any remaining estimation errors on MP performance, provide scientific advice on the suitability of the EM for the proposed bigeye MP, and consider recommending the continued application of the Estimation Method.

Background:

WCPFC22 requested the SSP to evaluate candidate MPs controlling longline and purse seine fisheries through a continuum of HCR combinations designed to achieve specified target reference points (TRPs). Following BMW01 and SC22, BMW02 considered updated MSE evaluations and agreed to focus on three WCPO-wide areas and fisheries of application for further evaluation: (i) all longline fisheries included; (ii) excluding SIDS and Territories, consistent with the exemptions under the Tropical Tuna Measure (TTM); and (iii) excluding SIDS and Territories and the Hawaii longline fleet. BMW02 also retained two target-type TRPs, corresponding to 0.94 and 1.06 times the 2012–2015 average spawning biomass depletion, each with a 50% probability of being at or above the target. BMW02 considered alternative HCR formulations and defined the formulation to be used in future work, and examined the implications of stock status declining below the target. Further evaluations are intended to inform the scientific assessment of candidate MP performance, including stock status, LRP risk and fishery outcomes, before WCPFC23.

SSSC01 Action: 

SSSC01 will review the updated MSE results for the candidate MPs retained by BMW02, focusing on the scientific reliability of the evaluations, performance relative to the LRP, achievement of the respective TRPs, and differences in biological and fishery performance indicators. The review may assess how the revised OM reference set and HCR design influence MP performance and identify any significant scientific uncertainties or limitations that may affect the interpretation of the evaluation results. SSSC01 will consider the provision of comparative scientific advice on the performance of the candidate MPs to WCPFC23, which may highlight key trade-offs, scientific uncertainties, and any limitations relevant to the Commission's management decisions.

Background:

The development of candidate bigeye MPs has highlighted uncertainties associated with catches from fisheries outside direct MP control, including domestic fisheries in Indonesia, the Philippines, and Viet Nam. BMW02 requested the SSP to undertake robustness and sensitivity analyses for the narrowed range of candidate bigeye MP options identified through the Workshop, particularly to assess how plausible changes in catches from fisheries outside MP control could affect management outputs for MP-managed longline and purse seine fisheries. BMW02 also noted the potential implications of substantial revisions to historical catch data in the Western Pacific East Asia (WPEA) region for MSE results. Completion of outstanding MSY-based performance indicators was considered desirable, along with the provision of further information on the relative contributions of fisheries to stock depletion, subject to the BMW02’s prioritisation of scientific work before WCPFC23. That prioritized list of requests for the SSP is available in the BMW02 summary report.

SSSC01 Action: 

SSSC01 will review the available robustness and sensitivity analyses requested by BMW02 for the refined candidate MPs, particularly the effects of alternative catch assumptions for fisheries outside MP control on stock outcomes, LRP risk and management outputs for MP-managed longline and purse seine fisheries. Consideration may be given to potential impacts of these uncertainties on candidate MP performance, particularly LRP risk and projected management outcomes.

Background:

WCPFC21 agreed to a sequenced approach to determining management objectives for bigeye and yellowfin tuna, which was reaffirmed at WCPFC22. Under the mixed-fishery framework, yellowfin is indirectly managed through the MPs for skipjack, bigeye, and South Pacific albacore. SC22 adopted the yellowfin OM reference set and supported the yellowfin MSE framework. The preliminary projections presented at SC22 indicated a low risk of yellowfin falling below its LRP but suggested that the existing yellowfin management objective of maintaining spawning biomass depletion at or above the 2012–2015 average may not be achieved under the bigeye MP scenarios evaluated. As these projections did not incorporate the implications of the revised bigeye OM reference set developed following SC22, BMW02 requested the SSP to update yellowfin projections using the refined subset of bigeye MP options, including relevant yellowfin performance indicators, for consideration at the Special SC Session and WCPFC23.

SSSC01 Action: 

SSSC01 will review the updated yellowfin projections under the refined bigeye MP options, focusing on projected stock status, LRP risk, performance relative to the existing yellowfin management objective, and associated fishery outcomes. SSSC01 may assess the scientific implications of alternative bigeye TRPs and management configurations for yellowfin, taking into account relevant interactions with the skipjack and South Pacific albacore MPs, and identify any significant uncertainties or limitations.

Background:

SC22 welcomed progress made by the ISC’s Pacific Bluefin Tuna Working Group (PBFWG) and the Joint IATTC and WCPFC-NC Working Group on the Management of Pacific Bluefin Tuna (PBFJWG) towards developing a long-term harvest strategy. ISC provided updated PBF MSE information, including calculations of initial total allowable catches (TAC1) under newly requested HCRs and methods for deriving conversion factors among fishery management categories. Although full MSE results for previously evaluated HCRs had been presented at SC21, the newly proposed HCRs had not undergone full simulation testing due to time constraints. ISC indicated that their performance could generally be inferred from previously tested HCRs, as they fell between those candidates and were not expected to pose substantial stock risk. ISC also indicated that full simulation testing would be undertaken once an MP was adopted. SC22 considered that, in principle, any MP proposed for Commission adoption should undergo full MSE simulation testing and SC review before adoption. At the time of SC22, no agreed MP recommendation had been reached by the PBFJWG, and no proposal from NC22 had been submitted to SC22 for recommendation to the Commission. SC22 therefore agreed to revisit the matter at the Special SC Session. Subsequently, PBFJWG11(2) in August 2026 adopted an interim PBF MP and forwarded the associated draft WCPFC CMM to NC22-2 for resolution of outstanding allocation issues and finalization. Following adoption of the interim PBF MP by IATTC104 in September 2026, NC22-2 is expected to consider the PBFJWG11(2) recommendation and associated CMM before SSSC01, with a view to forwarding recommendations to WCPFC23 for adoption.

SSSC01 Action: 

The Special SC Session should review developments since SC22, including the interim PBF MP recommended by PBFJWG11(2), its subsequent adoption by IATTC104, the outcomes of NC22-2, if available, and updated scientific information from ISC. 

Background:

BMW01, BMW02, and SC22 identified several matters relevant to the future operation of the bigeye MP, including monitoring requirements, robustness testing, exceptional circumstances, and interactions with existing tropical tuna management measures. SC22 also noted that the mixed-fishery monitoring strategy for bigeye and yellowfin is scheduled for development and adoption in 2027. For Pacific bluefin tuna, developments following PBFJWG11(2), including further MSE testing and consideration by NC and IATTC, may identify additional scientific issues concerning the long-term operation, monitoring, and evaluation of the PBF MP that are not fully addressed under the dedicated agenda item.

SSSC01 Action: 

SSSC01 may consider any additional scientific matters relevant to the adoption or future operation of the bigeye and Pacific bluefin tuna MPs that are not addressed under preceding agenda items. Where appropriate, SSSC01 may identify outstanding technical issues requiring further consideration by the SSP, ISC, or relevant scientific bodies, particularly concerning monitoring strategies, robustness testing, exceptional circumstances, and future MP evaluation.

SSSC01 will review and adopt its outcomes, including any recommendations to WCPFC23. The SSSC01 Summary Report will be finalized intersessionally.

The Chair may invite closing remarks by participants before closing the First Special Session of the Scientific Committee.