大槌川に回帰するシロサケの研究-II. : 成熟魚の沿岸から河川への移動

概要

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Mature chum salmon (Oncorhynchus keta WALBAUM) apeared at Otsuchi Bay during late October to late December 1959. The largest daily catch was seen during late November and the total catch by 18 trap nets was 19, 478 fish for this season. Mature chum salmon that swam up the Otsuchi and Kotsuchi Rivers to spawn during late October to early and middle December 1959, and the total salmon catch in Otsuchi and Kotsuchi Rivers was 4, 733 and 313 fish, respectively. Only a few chum salmon entered Unosumai River during this year. It may be said from comparisons of the catches from each trap net along the shore line of Otsuchi Bay that a majority of the mature chum salmon that migrate into Otsuchi Bay move toward Otsuchi River along the northern shore of the bay. It may also be said from the succession of large daily catches among the trap nets along the northern shore line of Otsuchi Bay that mature chum salmon schools take roughly eight days to reach the end of the bay from the mouth of the bay. In this interval, the salmon seem to stay at the inner part of the bay for several days. Mature chum salmon schools which reach the end of Otsuchi Bay seem to swim up the Otsuchi River mainly within one or two days after reaching the end of the bay.