Abstract for Foodweb workshop on September 13-14 Yokohama
Hiroyuki Matsuda, Tapan K. Kar and Peter A. Abrams
Ecosystems, including those that contain fisheries resources, are characterized by uncertainty, dynamic properties, complexity and evolutionary responses of the component species. However, the classical maximum sustainable yield (MSY) theory does not include any of these. Thus, it is perhaps not surprising that the MSY theory and its derivatives have not worked for fisheries management. Therefore, in this century, we need to consider how to use non-stationary bioresources. We investigate the effects of species interactions on sustainable yield from an exploited multispecies community. We consider the consequences of feedback control in fishing effort. If the prey species is exploited, increasing fishing effort decreases the predator abundance more than the prey abundance. Feedback control of fishing effort may cause extinction of the predator, undesirable stock and catch fluctuation, and a long fishing-ban, even if the prey population is controlled under a given feedback rule. In a multispecies community, feedback control of fishing effort on a particular species may cause extinciton of other species. Therefore, we make the following recommendations that could both increase the food resources derived from fish and reduce the chances of overexploitation or extinction: (1) Catch fish at lower trophic levels; (2) Switch the target fish to correspond to the temporally dominant species; (3) Monitor not only the target stock level but also any other indicator of the ügentireüh ecosystem.