Survival of Juvenile Salmonids Passing through Bypass Systems, Turbines, and Spillways with and without Flow Deflectors at Snake River Dams

Using yearling chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss tagged with passive integrated transponders (PITs), we estimated passage survival through bypass systems, turbines, and spill bays with and without flow deflectors at Snake River dams relative to survival of fish released into the tailrace below the dam. Actively migrating fish were collected and marked with PIT tags at Snake River dam smolt collection facilities. Groups of tagged fish were then released through hoses into different passage routes; releases were coincident with a tailrace release approximately 1–2 km below the dam. Relative survival was estimated by the use of tag–recapture models for paired releases from detections of individual PIT-tagged fish at juvenile collection or detection facilities at downstream dams. Detection sites included Little Goose, Lower Monumental, McNary, John Day, and Bonneville dams, depending on the release location and year. Standard errors of relative survival probability estimates were generally less than 3.0% through all potential passage routes. The estimated relative survival was highest through spill bays without flow deflectors (98.4–100%), followed by spill bays with flow deflectors (92.7–100%), bypass systems (95.3–99.4%), and turbines (86.5–93.4%). These estimates of relative survival, which include both the direct and indirect effects of passage, are generally higher than past estimates but similar to other recent estimates determined with modern techniques under present dam configurations and operating conditions.