Homogenization of the timing of chum salmon returns in relation to hatchery transplantation

Abstract

The timing of migration and breeding is an important aspect in the study of the migratory ecology of fishes. This timing in fish is generally determined by both genetic and environmental factors but is also subject to anthropogenic selection. Hatchery transplantation practices, where hatchery fish are produced from returned adult salmon and then transplanted into several rivers, have been going on for over 30 years in the southern part of Hokkaido Island, Japan. In this study, I compared the inter-river variation in timing of spawning migration in chum salmon to examine the effects of hatchery transplantation on the timing of migration. There was less inter-river variation in the timing of spawning migration in transplanted rivers than in non-transplanted rivers. This result suggests that hatchery transplantation homogenizes the timing of spawning migration in chum salmon. Changes to other resource management tools, such as promoting natural spawning and/or hatchery releases using local fishes, may be important to preserve diversity in the timing of migration.