三陸沿岸に回帰するサケ親魚の行動

抄録

The migratory behavior of chum salmon Oncorhynchus keta approaching their natal river was studied using ultrasonic tracking and conventional tagging procedures off the coast of Sanriku in 1984 and 1985. Tracking directions of sonic tagged salmon were mainly to the north and south along the coast. The moving area exhibited by salmon was within five nautical miles of the coast. Swimming depth dominated upper 20m in depth. Salmon showed a tendency to orient to the coast during daytime and ebb tide. The differences in precision of orientation to the coast between daytime and nighttime was statistically significant with chi-square test, and ebb tide and flood tide not significant. The periods of movement estimated by salmon with con-ventional tag from released point to recaptured were revealed by movement of sonic tagged salmon. We conclude that the orientation of chum salmon approaching their natal river is related to a diurnal periodicity and tidal currents. The migration of chum salmon is extensive along the coast before entering their natal river.