Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8883
Title: Preliminary evaluation of the Bonneville juvenile bypass system—Second Powerhouse
Author/Editor: Robert J. McConnell, William D. Muir
Publication Year: 1982
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon

Construction work on the second powerhouse at Bonneville Dam extended through the 1982 fingerling migration period.  In addition, high river flows during spring and summer 1982 necessitated the spilling of excess water throughout this period.  These two factors influenced the results of preliminary studies conducted by NMFS personnel.  Of fish released on 23 April, 0.37% of those released into the tailrace and 0.39% of those released into the DSM gallery downwell were recovered—not a statistically significant difference.  Consequently, we concluded that fish that entered the downwell in the DSM gallery and were transported downstream from the second powerhouse survived as well as those released directly into the tailrace.  Apparently there were no obstructions that would impact juvenile survival in that portion of the DSM.

The 10% sampler was exceptionally accurate:  of 2, 2 31 marked fish released into Gatewell 18B, 9.9% were recovered by the sampler.  Approximately 6% of the fish recovered were descaled.

Gatewell dipping of unmarked fish in the first and second powerhouses showed wide variation in descaling between species, with averages ranging from 7 to 17%.  This effort will be expanded in 1983.

During 938 h of DSM operation, 8,927 fish were obtained from the 10% sampler.  Subyearling fall Chinook salmon were captured most frequently and had the least descaling (4.4%) where as sockeye salmon were captured less frequently; however, they sustained the highest rate of descaling at 48.9%.