Refinements of the BR CMP as at July 2021

The BR CMPs first advanced by Butterworth and Rademeyer (2021) are first refined, and then their tuning parameters are adjusted to meet the development tuning options specified at the April 2021 meeting of the Bluefin Tuna Species Working Group for the reconditioned OMs. Discussion focuses on the results from the stochastic runs of these CMPs, as ultimately any MP eventually adopted will need to show satisfactory performance for such scenarios, which better reflect reality for future data. The lower tuning targets yield results that would likely be considered unacceptable because of a fair number of OMs for which especially low percentiles of Br30 distributions are rather small. Hence, future CMP options considered should probably be restricted to tuning targets for the eastern and western stock median (over the grid OMs) Br30 values which do not extend much below 1.5 and 1.25 respectively. The resource conservation performance for some of the robustness tests is open to question, more so for the western stock.