Is B₁ = K an appropriate assumption when applying an observation error production-model estimator to catch-effort data?

Abstract

A Monte-Carlo simulation approach is used to investigate the relative robustness of the results of the Butterworth–Andrew (B ₁ = K and B ₁ estimated) dynamic production-model observation-error estimators to different "true" values of the ratio of initial biomass B ₁ to unexploited equilibrium biomass K. The simulations use an underlying operating model typical of that appropriate for stocks of Cape hake off southern Africa. The B ₁ = K variant of the estimator results in lower estimated expected discrepancies for a number of management quantities over a wide range of the value of the "true" ratio. In addition, it is less likely to provide severe overestimates of the f _0.1 total allowable catch (TAC). Not all management quantities are equally sensitive to the value of the "true" ratio. In particular, f _0.1) TACs can be severely overestimated, although the maximum sustainable yield (MSY) is relatively well determined over a wide range of values of the ratio. It is therefore recommended that harvesting strategies which do not permit TACs to be set in excess of the estimated MSY be preferred.