LAUSR

To determine the optimal shape of the harvest control rule (HCR) achieving common fisheries management objectives (maximizing the average catch, reducing the deviation of yields, and avoiding stock collapse) and ensure robustness to observation errors, we estimate the optimal values of biological reference points (BRPs) composing the HCR. While traditional HCRs usually consist of three BRPs based on the fishing mortality coefficient (F3-HCR), we introduce an alternative HCR defined by 21 BRPs based on the catch levels (C21-HCR) to cover various possible shapes of HCR including smooth ones. We compare the shape and the performance between the optimal C21-HCR and the optimal F3-HCR and conclude that the optimal HCR can be composed of the gradual combination of the basic strategies: the constant escapement strategy, the constant harvest rate (CHR) strategy, and the constant catch strategy. However, the current F3-HCR does not necessarily allow this combination and generally returns lower performance levels than the optimal C21-HCR (since the basic strategy is confined to CHR) excluding the range of low biomass. This result will provide a clear perspective to improve HCR according to the magnitude of assessment errors and to compromise multiple fisheries management objectives when various stakeholders are involved.