Genetic Interactions between Hatchery and Wild Fish: Japanese Chum Salmon Perspectives

The Japanese chum salmon hatchery program successfully increased fishery production since 1970s with average return rates of 3.7±1.2% in Hokkaido and 1.7±0.6% in Honshu. In the recent decades, return rates consistently decreased with large variations, and the decreasing trend is steeper in Honshu. However, little is known about genetic effects of Japanese chum salmon hatchery practices. Here, we review literature on this subject, and describe an overview on interactions between hatchery and wild chum salmon. Intensive Japanese chum salmon supplementation for early run populations altered the distribution of run timing of chum salmon in Hokkaido, but the genetic diversity remains high compared with other populations in the Pacific Rim. Empirical Bayes microsatellite F_ST described a fine scale population structure consisted of seven regional groups (five in Hokkaido, two in Honshu), generally agreeing with previous studies, but some populations were nested which might reflect translocation history of hatchery fish. The mitochondrial DNA control region F_ST was approximately six times larger than that for the microsatellite loci, and resulted in a stepping stone structure with persistent translocation effects, suggesting more conservative female toward spawning grounds (smaller straying).We will discuss on fitness of hatchery fish and future challenges for Japanese chum salmon hatcheries.