The Increasing Threat Posed by Nonnative and Hatchery-Reared Salmonids to Japanese Wild Native Salmonids

Japan has eight native salmonid species, and stocking with nonnative salmonids from foreign and domestic regions is posing problems for the conservation of these native species. In particular, species replacement of native white-spotted charr by nonnative brown trout and rainbow trout is now a serious issue in some streams. Interspecific interactions such as competition and hybridization are thought to be the prime mechanisms of this replacement. Moreover, recent studies suggest that stocking with hatchery-reared native species also damages wild populations of native species. Hatchery-reared fish outcompete wild fish, and hybridization between them transmutes the genuine genetic background of wild populations. Hybridization sometimes also alters the life history of wild populations. These stockings have been conducted for fisheries purposes and for civic environmental education, but they are likely to have results opposite to those expected by fisheries managers. From a Buddhist perspective, many Japanese people believe that allowing animals to escape from cages is an act of goodwill, and especially this belief is a cause of widespread stocking as civic environmental education. To solve these problems, we need to develop not only government systems but also public education campaigns based on biological knowledge.