The Seasonal Variation of the Good Fishing Area of Salmon and the Movements of thewater masses in the Waters of Western North Pacific-‡U. The distribution and migration of salmon population in offshore waters Kisaburo TAGUCHI To know the relation between the movement of water mass and the migration of salmon

FOR RED SALMON (Oncorhynchus nerka) 1961 Kisaburo TAGUCHI* As to the consideration about the rationality of offshore fishing for chum salmon, it has been tried in the previous paper (1) of this report on the basis of the estimation of the ins tantaneous rate of natural mortality. Also in red salmon, since the same kinds of data have been given, the same estimation and consideration for red salmon were tried with the same purpose and method. Adopting the symbols as bellow equally in the case of chum salmon, next formulas are given. R0¥¥¥¥Size of mature salmon run in number of fish in offshore waters. R¥¥¥¥Size of mature salmon run in number of fish in coastal areas. C¥¥¥¥Catch of offshore fishing. C1¥¥¥¥ Catch of coastal fishing. M0¥¥¥¥Instantaneous rate of natural mortality. M1¥¥¥¥Instantaneous rate of mortality by net-mark. F0¥¥¥¥Instantaneous rate of fishing mortality. F1¥¥¥¥Instantaneous rate of occurrence of net-mark. t0¥¥¥¥Term of offshore fishing (Number of day). t1¥¥¥¥Term of migration from offshore to coast (Number of day).

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In 70% of main rivers in Hokkaido, all chum salmons entered to the rivers are caught and used for artificial propagation and it is estimated that 90% of chum salmon runs are brought about by artificial propagation.For the above reason, the effect of artificial propagation can be estimated by studying the relation between the number of parent fish caught in the rivers and the number of total catches both in the rivers and the coast of Hokkaido in the returning year .In this paper, above relation is studied by using Ricker's formula (R=aEe-bE) , and the estimates are given as follow: 1) In Hokkaido, the effect of artificial propagation for chum salmon shows two times the recruitment as compared to that of natural spawning .2) In the present environment , the most effective number of fry released from hatcheries are about 360 millions. In this case seven fishes of return are expected per parent fish .

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