Management under uncertainty: defining strategies for reducing overexploitation

Abstract

To reduce overexploitation is a familiar problem for fisheries management. A direct reduction of fishing mortality rate to F_max (or F_0.1) implies a corresponding decrease in total allowable catch (TAC) in the short term which is likely to create severe problems for the industry. Moreover, conventional management strategies usually aim at either maximizing yield (F_max) or stabilizing fishing effort (F_stq), and, as noted previously by various authors, these criteria are often simultaneously incompatible. Hence, fishery managers have to find a compromise between several objectives: short term versus long term, maximum yield versus stability of fishing effort and yield, and so forth. This study aims at determining compromise TAC management rules that could fulfil these conditions. Uncertainties in data used for assessment are taken into account as a potential source of error in scientific advice. A simulation-based approach allows the properties of conventional and compromise strategies to be analysed on both short- and long-term time horizons. In the case of compromise strategies, yield and fishing effort are found to be less sensitive to uncertainties and hence more stable and easier to forecast. By these measures, overexploitation can be rectified relatively quickly without serious loss of yield in the short term.