RETURNING EFFECT AND ITS LIMIT RESULTING FROM THE ARTIFICIAL PROPAGATION FOR CHUM SALMON IN HOKKAIDO
1965 Volume 31 Issue 5 Pages 323-326
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1965 Volume 31 Issue 5 Pages 323-326
In70% 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.
