Increase in maturation size after the closure of a high seas gillnet fishery on hatchery-reared chum salmon Oncorhynchus keta

Gillnet fisheries are strongly size-selective and seem to produce changes in size at maturity for exploited fishes. After Word War II, large-scale gillnet fisheries targeted Pacific salmon (Oncorhynchus spp.) in the high seas area of the North Pacific and the Bering Sea, but these fisheries were closed in 1993. To assess the effects of this high seas gillnet fishery (and its closing) on size at maturity, we examined long-term trends in size at 50% probability of maturing (L50) for chum salmon (O. keta) from three populations in Hokkaido, Japan. The L50 trends were statistically different among rivers, but showed similar temporal patterns with decreases in the 1970s and early 1980s and increases after the 1985 brood year. While fishery-induced evolution seemed largely responsible for this temporal change in L50 during the fishing period, natural selection and phenotypic plasticity induced by environmental changes could contribute to the increases in L50 after the relaxation of fishing pressure

SALMON STOCK VARIABILITY AND THE POLITICAL ECONOMY OF THE PACIFIC SALMON TREATY

Since the mid-1970s, changes in the marine environment along the west coast of North America and in the Northeastern Pacific appear to have greatly enhanced the productivity of Alaskan salmon runs while contributing to declining runs of some salmon spawning in Washington, Oregon, and California. These inverse fluctuations in northern and southern salmon stocks may have aggravated a recent break-down in cooperation between the United States and Canada in setting harvest allocations under the Pacific Salmon Treaty. This paper examines the establishment of fishing regimes by the Pacific Salmon Commission. A game theoretic model is used to analyze the possible contribution of stock variability to the current conflict. Shifts in the parties' incentives to manage the fishery cooperatively, together with significant transaction costs, explain much of the recent difficulty in negotiating mutually acceptable fishing regimes. The paper concludes by addressing the question of whether the regime-setting process can be made more resilient to such stresses. Copyright 1996 Western Economic Association International.