Hakozaki, Kyushu University
Modern fisheries are are characterized by the persistent danger of overfishing. In heavily exploited stocks, adaptive changes in life history and behavior seem to occur within just a few generations. Also, the ecological interactions within communities exposed to harvesting are often so complex, that the ultimate effects of fishing pressures are difficult to predict. Even though similar considerations arise in wildlife management, they are not yet well included in the theory and practice of contemporary resource management. This session addresses implications of adaptive changes and community dynamics for the sustainable management of living resources. (revised)
Effects of predator-prey interactions and adaptive change
on sustainable yield
Hiroyuki Matsuda (Yokohama National University) email@example.com
Ecosystems including fisheries resources are characterized by uncertainty, dynamic properties, complexity and evolutionary response. However, the classical maximum sustainable yield (MSY) theory does not include any of these but assumes (1) perfect information about the stock-recruitment relationship and stock abundance, (2) stable equilibrium, (3) a single stock management and (4) fixed life history irrespective of fishing mortality. The MSY theory and its derivatives have not worked for fisheries management (Hilborn 2002, Matsuda & Abrams 2006).
FAO (Food and Agriculture Organization of U.N. 2000) noted that about 3/4 of stocks are either fully exploited, overexploited, have been depleted or are recovering from depletion. It should be noted, however, that although the total landings of demersal fishes was saturated by the 1970s, those of pelagic fishes are still increasing, These pelagic fishes fluctuate in stock abundance greatly even without fisheries. When the stock level is at a low level, the impact of fisheries on pelagic fishes prevents the stock from recovering (Kawai et al. 2002). Therefore, in this century, we need to consider how to use nonequilibrial bioresources (Matsuda & T. Katsukawa 2002, T. Katsukawa & Matsuda 2003). 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 the technology for selective fishing; (5) monitor not only a target species, but its prey and predator and the ecosystem.
Evolutionary responses of resources to fisheries often support counterintuitive policies, e.g., exploitation of smaller fishes (Conover & Munch 2002) and of spawners (Law & Grey 1998). We should take care of scientific meaning of result from studies in evolutionary ecology (Matsuda & Abrams 2004).
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FAO Fisheries Department (2000). The state of world fisheries and aquaculture. http://www.fao.org/sof/sofia/
Heino M (1998) Management of evolving fish stocks. Canadian Journal of Fisheries and Aquatic Sciences 55: 1971-1982.
Hilborn R (2002) The dark side of reference points. Bull Mar Sci 70:403-408.
Katsukawa T, Matsuda H (2003) Simulated effects of target switching on yield and sustainability of fish stocks. Fisheries Research 60:515-525
Kawai H, Yatsu A, Watanabe C, Mitani T, Katsukawa T, Matsuda H (2002) Recovery policy for chub mackerel stock using recruitment-per-spawning. Fish. Sci. 68:961-969.
Law R, Grey DR (1989) Evolution of yields from populations with age-specific cropping. Evol Ecol 3: (4) 343-359.
Matsuda H, Katsukawa T (2002) Fisheries Management Based on Ecosystem Dynamics and Feedback Control. Fish Oceanogr 11: 366-370
Matsuda H, Abrams PA (2004) Effects of predator-prey interactions and adaptive change on sustainable yield. Can J Fish Aq Sci 61:175-184
Matsuda H, Abrams PA (2006) Maximal yields from multi-species fisheries systems: rules for systems with multiple trophic levels. Ecol Appl 16:225-237