October 10-18, 2003, at the Conference Hall of the Mayfield Hotel, Seoul, Korea.
Hiroyuki MATSUDA, (Ocean Research Institute, University of Tokyo, Japan)
Ecosystems including fisheries resources are characterized by uncertainty, dynamic property, complexity and evolutionary response. However, the classical maximum sustainable yield (MSY) theory does not include any of these. The MSY theory and its derivatives have not worked for actual fisheries management. The pelagic fishes fluctuate greatly even without fisheries. In addition, the impact of fisheries on pelagic fishes when it was at low levels is too high to recover. I propose five principles: (1) Do not catch fishes that are at low stock levels; (2) Do not catch immature fishes but catch adult fishes; (3) Catch fishes that are temporally dominant; (4) In order to achieve these three principles, improve a technology for selective fishing; (5) Monitor not only a target species, but its prey and predator and the ecosystem. I also investigate the effects of predator-prey interactions on sustainable yield from an exploited predator-prey system. If the predator is exploited, it may increase in population size with increasing fishing effort, when the predator overexploits its prey. The effort that achieves MSY can be close to the effort at which the stock collapses. If the prey species is exploited, increasing fishing effort decreases the predator density more than the prey density. Feedback control of fishing effort may cause extinction of the predator, even if the prey population is well controlled. All of these results suggest that a non-equilibrium world with adaptive behaviour is quite different from the equilibrium world assumed in most fisheries management models.
Key words adaptive management, prey-predator interaction, maximum sustainable yield, pelagic fishes