Numerical investigation of the optimal control rule for decision-making in fisheries management

Recently, control rules (CR) have been widely used for decision-making of fisheries management. A CR describes fishing pressure (usually fishing mortality, F) as a function of some other variable(s) related to the status of the stock. The prevailing CR aim to achieve F-MSY. The main idea of CR is to change fishing pressure based on stock conditions. Therefore, it seems irrational that the goals of prevailing CR are defined by the constant harvesting rate (CHR) strategy The objective of the present study was to develop a method by which to numerically search for the optimal CR, apart from the traditional biological reference points based on CHR. I also compared the performance of the optimal CR and those of the prevailing CR (F-MSY, 75%F-MSY, New Management Procedure of the International Whaling Committee and the CR in US guidelines). The result suggested that the limitation of maximum fishing mortality was effective for stocks with low natural mortality and large stock size estimation error, while the biomass threshold was effective for stocks with short longevity and small estimation error. This means that the optimal CR is sensitive to the life history and uncertainty of the stock. Therefore, there seems to be no 'one-size-fits-all' rule for fish stocks.