We evaluated the survival of juvenile salmon through turbines in Columbia River dams and found no differences between two operations but strong evidence of delayed mortality from turbine passage. After tagging with a passive integrated transponder (PIT) tag and a radio tag, yearling Chinook salmon Oncorhynchus tshawytscha were released at McNary Dam on the Columbia River through a turbine operating both within 1% of peak efficiency (a discharge rate of 317 m3/s) and outside the 1% range at the maximum blade angle (464 m3/s). Estimated relative survival to a detection array 15 km downstream was 0.871 at 317 m3/s and 0.856 at 464 m3/s and 0.858 and 0.814, respectively, to an array 46 km downstream. The highest point estimates of survival occurred under the lower discharge, suggesting that operating turbines within 1% of peak efficiency is a useful guideline for fish protection at McNary Dam. In a concurrent evaluation using balloon tags, estimated mean direct survival ranged from 0.930 to 0.946. Radio tag estimates were significantly lower than balloon tag estimates under both operations. Based on these differences, we estimated that delayed mortality comprised from 46% to 70% of total estimated mortality. We reviewed the literature and concluded that delayed mortality was caused by sublethal impacts to fish sensory systems, which increased vulnerability to predation in the tailrace. We recommend that future research to improve turbine designs and operations for fish passage focus on this major component of mortality.

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At Pacific Northwest hydroelectric dams, surface containers or hose systems have been used to release marked juvenile Pacific salmon Oncorhynchus spp. for fish passage studies. Because these release methods introduce marked fish to unknown depths and hydraulic conditions, they may compromise study results. We constructed a canister and frames for releasing marked fish at predetermined depths and locations in the gatewells and forebays of hydroelectric dams. The canister performed as anticipated, avoiding injury to fish and allowing them to acclimate to depth prior to release. Acclimation is accomplished by slowly lowering the canister to the desired depth and holding the canister for a period of time before release. A total of 1,000 yearling and subyearling chinook salmon O. tshawytscha were released with this canister over a 2-year period in studies of guidance and orifice passage systems. About 98% of these fish were recaptured, with no injury or descaling attributed to the release canister. This release method allows time for acclimation as well as repeatable positioning of the canister for release of fish at depth for studies at hydroelectric dams on the Columbia and Snake rivers.