MEPS 291:307-312 (2005) - doi:10.3354/meps291307
First record of the at-sea swimming speed of a Pacific salmon during its oceanic migration
Hideji Tanaka1,2,7,*, Yasuhiko Naito1, Nancy D. Davis3, Shigehiko Urawa4, Hiroshi Ueda5, Masa-aki Fukuwaka6
ABSTRACT: The swimming behavior of the chum salmon Oncorhynchus keta was studied for 53 d of its 67 d oceanic migration from the central Bering Sea to the Japanese coast. We provide the first data on swimming speeds by a homing salmon, recorded at 5 s intervals by a fish-borne time-speed, depth, and temperature logger. Swimming speed rarely exceeded 1.0 m s1, and horizontal swimming speed was 36.4 ± 15.2 km d1. Cumulative horizontal swimming distance was approximately 2500 km, equivalent to 90% of the minimum distance between the release and recovery sites (2760 km). Swimming depth and speed peaked around dawn and dusk, and there was a smaller peak around midnight. The fish showed sequential up-and-down movement near the thermocline during daytime. Diurnal patterns of movement suggest that homing chum salmon spend a considerable time foraging, and the strategy is different between daytime and nighttime. Our findings indicate that over large distances of ocean, a homing salmon maintains a strong homeward orientation, but that passive transport by favorable water currents may help the migration.
KEY WORDS: Chum salmon · Oceanic migration · Swimming speed · Orientation · Time allocation · Foraging behavior
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