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Handling-induced delay and downstream movement of adult chinook salmon in rivers
By David R. Bernard, James J. Hasbrouck, Steven J. Fleischman
Fisheries Research, Volume 44, Issue 1, November 1999, Pages 37-46, ISSN 0165-7836, DOI: 10.1016/S0165-7836(99)00056-9.
We provide evidence that adult chinook salmon Oncorhynchus tshawytscha handled in riverine studies migrate differently upon release from their uncaptured peers. Adults with radio transmitters were released into the Kenai River, Alaska in July 1996 and 1997 while migrating chinook salmon were counted with split-beam sonar. Of known upstream migrants, 72% in 1996 and 46% in 1997 dropped downstream at least 3 km and typically delayed their upstream migration by 4-5 d with some delaying beyond 30 d. In contrast, at most 9% of migrants counted with the sonar were moving downstream. Delay, mortality rates, rates of transmitter failure, and capture rates in downstream fisheries were similar to statistics from other studies. No evidence was found to link downstream movement and delay to size, sex, or migratory timing of chinook salmon. Handling-induced behavior will bias estimated transit times and can bias abundance estimates from capture-recapture experiments, but should not bias estimates of migratory timing or distribution of spawning chinook salmon within a watershed.
Keywords: Chinook salmon; Split-beam acoustics; Radio telemetry; Handling-induced behavior; Bias