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This working paper describes developments on the Indian Ocean Tuna Commission (IOTC) yellowfin (YFT) reference set and robustness test operating models (OMs), since the 2019 Working Party on Tropical Tunas (WPTT) and Working Party on Methods (WPM). In the following (for historical reasons), we mostly use the term MP and Management Strategy (MS) interchangeably, though we subscribe to the specific definition of MP as a subset of MS (as defined in the CCSBT and IWC, in which the MP aims for full specification and simulation testing of data collection and analytical methods). Management Strategy Evaluation (MSE) is the simulation testing process, using complex operating models, for evaluating performance of alternative MSs (or MPs). The intent was to obtain feedback on presentation requirements for the 2020 Technical Committee on Management Procedures (TCMP) meeting, and recommendations on further analyses and revisions for the OMs in preparation for the WPM and WPTT 2020 (but priorities changed due to the Covid-19 pandemic and remain uncertain).
There were requests for a number of YFT OM developments from the 2019 WPM and WPTT. These requests were made during a particularly busy WPTT meeting schedule, under the assumption that the OM changes would parallel the improvements realized through the YFT stock assessment update that was happening in parallel (at least that was our interpretation). However, the YFT assessment was aborted near the end of the formal WPTT meeting, and there was not time to discuss the implications of the various assessment innovations and their appropriateness for either future assessments or OM conditioning. The intent has always been that OM re-conditioning should not be required every year – only when there is evidence that the OM fails to adequately represent the plausible system uncertainty. In the absence of a revised stock assessment and a systematic discussion of proposed assessment/OM changes, we have interpreted the OM development requests as guidance for further investigation. However, it is not clear from the explorations undertaken to date that that we have improved the YFT OM relative to the previous iteration.
