MSYR—should the information which has become available since selections were made for RMP development in 1987 have changed perceptions on the likely range and relative plausibilities of values for this parameter for baleen whales

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University of Cape Town

It is argued that continued attempts to estimate MSYR from accumulating data, to refine the plausible range of values for this parameter and relative plausibilities within this range, cannot be other than a crucial component of the process of development (and, in due course, refinement) of the Revised Management Procedure (RMP) and of the interpretation of the results of the associated Implementation Simulation Trials (ISTs) for particular RMP applications. In 1987, when the range of MSYR values for RMP trials was first specified, four of the six independent sources of information available suggested definite "low" MSYR values (~1%). None of these four sources appears to have survived to the present. Estimates of MSYR for twenty populations have become available since 1987 - eleven based on population model fits and the balance on the relationship MSYR > r(0)/2. Two arguments advanced previously against the use of this last relationship are considered: the one is dismissed because it lacks support in empirical data, while the other appears negated by an analysis by Best (1993). In the fourteen cases where estimates of MSYR (in terms of uniform selectivity harvesting on the 1+ population) are determined with reasonable precision, most lie in the 2%-6% range, and only one of these has a lower 90 or 95% confidence/probability bound below 1%. Cases of low point estimates of MSYR show wide confidence intervals not incompatible with this 2-6% range. Thus, evidence forthcoming since 1987 (much of it subsequent to 1993 when the Scientific Committee last discussed this issue substantively) would seem to support a change in the Committee's perception at that time of the likely range of values for MSYR for baleen whale stocks, as well as informing judgments on the relative plausibilities of values within this range.