大槌川に回帰するシロサケの研究-I

Abstract

1. Nineteen chum salmon caught by a trap set in Otsuchi Rivers were tagged and released inside Otsuchi Bay. Among them, 13 tagged fish were recaptured in Otsuchi River. Eight chum salmon caught by a trap set in Kotsuchi River were also tagged and released inside Otsuchi Bay. Among them, 2 tagged fish were recaptured in Kotsuchi River. The results of the two experiments showed that the chum salmon return to a certain stream which the fish had once before ascended to spawn and this seems to be the parent stream of the fish. 2. Fourteen chum salmon caught by a trap set in Otsuchi River were transported to Kotsuchi River. After reserving them for 24 hours, these fish were transported again to a station inside Otsuchi Bay then tagged and released there. Among them, 2 tagged fish were recaptured in Otsuchi River, but none was recaptured in Kotsuchi River. The results of the experiment showed that the behavior of the chum salmon of returning to Otsuchi River does not change even after reserving the fish in another stream. 3. Eleven chum salmon caught by a trap net outside Otsuchi Bay were tagged and released there. Among them, one was recaptured in Otsuchi River and 2 in Otsuchi Bay, the other 6 fish, however, were recaptured in rivers and bays other than Otsuchi River and Otsuchi Bay. The results of the experiment showed that the cuum salmon reached a coast from the off sea and entered its parent stream after moving some distance north or south along the coast. 4. Twenty six chum salmon caught by a trap net inside Otsuchi Bay were tagged and released there. Among them, 8 were recaptured in Otsuchi River and one each were recaptured in Kotsuchi and Unozumi Rivers. The other 8 fish were recaptured inside the bay. The results of the tagging experiment showed that more than half of the chum salmon which entered Otsuchi Bay ascended the rivers emptying into the bay in a short time though some continued swimming around the bay for several days before the ascending rivers.