Studies on closely related species Salmo gairdneri and Salmo mykiss; their distribution and migration in the North Pacific and systematics

Seasonal distribution and migration patterns of the steelhead trout, Salmo gairdneri , and the Kamchatkan trout, Salmo mykiss , in the North Pacific were examined based on some biological data as well as allelic variations of enzymes. The comprehensive analyses indicated that the western segment of the population mainly consisted of the Kamchatkan trout. As the fish extended to the west from spring through summer, the distribution of the steelhead trout extended notably to the western North Pacific. In terms of genetic distance, the coastal group of the stellhead trout in North America was more close to the Kamchatkan trout than to the inland group of the steelhead trout. This finding, as well as other observations, indicates that the Kamchatkan trout and the steelhead trout should be recognized as a single species. Refuges for each group during the last glacial period and their postglacial dispersal are discussed based on their estimated divergence time.