Ecological Impacts of Rainbow, Brown and Brook Trout in Japanese Inland Waters

Abstract

　Rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis) introduced to Japanese inland waters have significant impacts on native aquatic organisms such as white-spotted charr (Salvelinus leucomaenis), Dolly Varden charr (Salvelinus malma), masu salmon (Oncorhynchus masou) and Sakhalin taimen (Hucho perri), in coldwater habitats. Rainbow and brown trout have successfully established reproducing populations in Japan, and especially expanding their distribution in Hokkaido. Brook trout have shown relatively limited invasion in some spring-fed streams and ponds both in Honshu and Hokkaido. The introduced exotic trout have been implicated in reducing populations of native fishes, especially stream salmonids, through predation, competitive interaction for resources, and interspecific hybridization. Monitoring, management, including eradication, and evaluation of the effectiveness of these measures should be carried out to contain the ecological risks of trout invasion.