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Reservoir provides cool-water refuge for adult Chinook salmon in a trap-and-haul reintroduction program

Naughton, George P., Keefer, Matthew L., Clabough, Tami S., Knoff, Matthew J., Blubaugh, Timothy J., Sharpe, Cameron, Caudill, Christopher C.
Marine & freshwater research 2018 v.69 no.12 pp. 1995-2007
Oncorhynchus tshawytscha, adults, biotelemetry, cumulative exposure, dams (hydrology), heat sums, risk, rivers, salmon, spawning, temperature, water, water reservoirs, Oregon
Trap-and-haul is a mitigation strategy at many hydropower dams lacking upstream fish-passage facilities, and protocols are needed to maximise its effectiveness. We used biotelemetry to assess the potential benefits of releasing transported adult Chinook salmon (Oncorhynchus tshawytscha) into a cold-water reservoir v. a relatively warm-water tributary before spawning. Over 5 years, we released 160 salmon into Foster Reservoir (Oregon, USA) and another 102 into the South Santiam River near historical salmon spawning areas further upstream. In total, 70% of reservoir-released salmon entered an upriver tributary after spending a median of 3–95 days annually in the reservoir. Data recovered from 61 archival temperature loggers indicated that salmon were ~3–6°C cooler per day in the reservoir than in the river. We estimated that cumulative exposure of reservoir-released fish was reduced by 64 degree days, on average (range=–129 to 392), relative to river-released fish. Release into the reservoir was not risk free; 14% of all reservoir-released fish fell back downstream v. 1% of river-released fish. We conclude that reduced transport distance, reduced thermal exposure and potential survival benefits of releasing salmon into reservoirs should be weighed against risks of factors such as fallback and homing errors.