The benefits of species-based management of sympatric mud crabs migrating to a common fishing ground

Abstract

The issue of effective fisheries management in sympatric species of mud crab of the genus Scylla on a local fishing ground is examined. A simple model is developed that allows the calculation of yield-per-recruit (YPR) based on deterministic body growth of two ideal coexisting crab species and their survival after migration to a fishing ground under two different fishing strategies. First, the basic strategy is traditional species-aggregated fishing, which does not distinguish the start of fishing and fishing effort among species. Therefore, the species-aggregated fishing strategy can be treated as if only a single species existed despite the coexistence of separate crab species on the fishing ground. This is in common use, because species discrimination of mud crabs is difficult. Second, an alternative strategy of species-based fishing is proposed, in which two fishing parameters are controlled depending on the demographic variables of each species. The application of the model to several combinations of individual growth rate (k) and natural mortality (M) between two species demonstrates that YPR for species-based management is larger than for species-aggregated fishing. Numerical simulations suggest that species-based fishing is advantageous even when fishing is controlled for only one species and the parameters of the other species are unknown. These findings could be applied not only to the effective management of sympatric mud crabs, but also to other overlapping species. © 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.