Abstract
Hatchery programmes involving the mass release of cultured fish have been implemented worldwide to supplement wild populations and to increase harvests. Hokkaido Island is one of the most active regions for Pacific salmon hatchery programmes, with ca. 1.2 billion (109) juveniles released annually along a coastline of ca. 3000 km. During the last quarter of the 20th century, coastal catches of chum and pink salmon increased dramatically, whereas those of masu salmon did not. In addition to the development of hatchery technologies, several possible hypotheses may explain these catch trends, including climate change, closing of high-seas fisheries, rehabilitation of water quality, habitat loss caused by damming and channelling, and increased pressure from recreational fisheries. Even when these other factors have been accounted for, it is difficult to evaluate whether all hatchery programmes have actually increased net populations. To use these programmes more effectively, it is necessary to evaluate both their river- and species-specific benefits and compare hatchery programmes with other management tools, such as fishery controls and habitat rehabilitation. Future hatchery programmes should incorporate active, adaptive learning approaches to minimize the risks associated with artificial propagation and to promote sustainable salmon stocks.
Skewed genetic sex ratio in reciprocal hybrids between pink salmon and masu salmon
