Distribution and migration paths of chum salmon populations distributed in the waters northeast off Japan from autumn to spring were examined based on allelic frequencies and some biological characteristics. Two distinct maturity classes, namely maturing and immature fish were observed among autumn collections and significant allelic differences were found between them. The allelic differences of maturing fish as well as their tag recovery data indicated that maturing chum salmon population mainly consists of the fish returning to Japanese rivers.
Since immature collections taken in autumn and maturing collections taken in spring during their northward shifts were statistically very similar, it is considered that the former has a link with the latter. Allelic frequencies of these fish corresponded better with known frequencies of populations of the Amur River area in the Soviet Union. The above as well as minimal tagging data suggest that the immature fish wintercd in southern waters and subsequently migrated to the north to approach the Amur River area as maturing fish.