抄録
Study of the boundary and the migration of salmon population in the western north Pacific is growing rapidly in importance for the states surrounding the North Pacific.
Fortunately, oceanographic investigations have been made since 1934 by Dr. Aikawa, Mr. Okamoto, and Dr. Uda, and exploratory fishing has been made by ten research vessels of the Japan Fisheries Agency in 1956 season in the waters from 160E to 180°E Long. and from 38°N to 48°N Lat.
These investigations made it possible to determine the relation between the change of the distribution of salmon population and the movements of water masses as foollows:
1. With respect to the sphere of distribution, that of the salmon having Asian origin coincides with that of the dichothermal water which shows Oyashio current, and the southern boundary of this sphere lie along the belt where the Kuroshio runs against the Oyashio.
2. The sphere of the distribution of salmon population is different according to species, pink salmon appear in the waters from the west side of 160°E Long. to the 5-6°C water, waters adjacent to Hokkaido, red and chum salmon appear in the waters from the east side of 160°E Long. to the south offing of the Western Aleutians with 3-4°C water. Red salmon migrate to the offing of the east coast of Kamchatka, chum and pink salmon migrate to the east offing of the North Kurile Islands with the north or northwestward movements of water masses.
3. The variation of the sphere of distribution and the change in the course of migration in each species of salmon suggest a tendency for the sphere of the distribution of the Oyashio to be separated from its original area where each species of salmon descended to the sea.
