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The Journal of Experimental Biology 204, 3895-3904 (2001)
© 2001 The Company of Biologists Limited

Swimming speeds and buoyancy compensation of migrating adult chum salmon Oncorhynchus keta revealed by speed/depth/acceleration data logger

Hideji Tanaka*,1, Yasuaki Takagi2 and Yasuhiko Naito1

1 National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan and
2 Otsuchi Marine Research Center, Ocean Research Institute, the University of Tokyo, Akahama, Otsuchi, Iwate 028-1102, Japan

*Present address: Biosphere Informatics, Department of Social Informatics, Kyoto University, Kyoto 606-8501, Japan (e-mail: htanaka{at}bre.soc.i.kyoto-u.ac.jp)

Accepted August 21, 2001

Although the homing migration of Pacific salmon is well documented, the swimming behaviour of the returning salmon has been poorly described, principally as a result of the difficulties encountered in monitoring salmon behaviour in the sea. The present study describes the use of a recently developed electronic data logger to obtain simultaneous recordings of the swimming speed, depth, fin-beating activity and body angle of free-ranging chum salmon Oncorhynchus keta during their homing migration in coastal waters. Chum salmon migrated horizontally at speeds of 1.5–3.0 km h–1. The gross horizontal distance salmon moved during total recording periods were 1.24- to 19.0-fold greater than the net distance from the release site to the retrieval points. It is suggested that homing salmon did not drift passively but swam actively to the spawning grounds. Salmon preferred the surface water, but also made frequent vertical migrations. The travelled depth of each salmon ranged from 0.36 to 0.64 km per hour. Salmon descended at faster rates and steeper angles than they ascended. Both tailbeat frequency and tail thrust were higher during the ascent than the descent phase. These results suggest that chum salmon spent more energy during the ascent than the descent phase. Profiles of descent rate assumed an arched shape with respect to a change in hydrostatic pressure, while ascent rate increased with decreasing depth. High tailbeat frequencies were found during the course of ascent, which suggests that the salmon did not regulate the volume of air in the swim bladder during short-term vertical migrations.

Key words: swimming speed, tailbeat frequency, angle, vertical rate, vertical migration, chum salmon, Oncorhynchus keta, homing migration, data logger.


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© The Company of Biologists Ltd 2001