Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 1162
Title: Passage behavior and survival of radio-tagged subyearling Chinook salmon at Lower Monumental Dam, 2008
Author/Editor: R. F. Absolon, Eric E. Hockersmith, Gordon A. Axel, Brian J. Burke, Kinsey E. Frick, Benjamin P. Sandford
Publication Year: 2010
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Walla Walla, Washington
Contract Number: W68SBV80438584
Pages: 52
Date: March 2010

We evaluated passage behavior and survival of subyearling fall Chinook salmon Oncorhynchus tshawytscha with the newly installed removable spillway weir (RSW) at Lower Monumental Dam.  For these evaluations, we collected river-run subyearling Chinook salmon from 6 June through 1 July 2008.  Fish were collected primarily at Little Goose Dam, with some additional fish collected at Lower Monumental Dam.

Study fish were surgically tagged with both a radio tag and passive integrated transponder (PIT) tag and released either 42 km upstream from the dam (treatment) or 1.25 km below the dam (reference).  Evaluations of survival were based on detections at Ice Harbor Dam, 52 km downstream from Lower Monumental Dam.

We released 2,362 radio-tagged fish as treatment groups and 2,071 as control groups.  Releases were made twice per day during the study period.  Of the 2,362 fish released to the forebay, 1,650 were used in the evaluation of relative survival.

Average total river flow was 106.4 kcfs during the study period, which was much higher than either 2006 (50.6 kcfs), 2007 (38.7 kcfs), or the 10-year average (65.4 kcfs).  In the last 10 years, there has only been one year (1999) when the average total river flow was higher than in 2008.

Estimated rates of relative survival were 0.879 for the dam, 0.932 for the concrete, 0.920 over the spillway, 0.974 for the RSW, 0.960 for turbines, and 0.928 through the bypass system.  Total spillway passage was estimated at 40.4% with 24% of fish passing through the RSW.  Estimated passage distributions were 46.2% via the juvenile bypass and 13.4% via turbines.  There were 63 fish (2.7%) that passed the dam via an unknown route.  Spill efficiency was estimated at 0.404, fish guidance efficiency at 0.775, and fish passage efficiency at 0.866.  Median overall forebay residence time was 2.3 h (range 0.3 to 139.2 h), and median tailrace egress time was 8.2 min (range 0.4 to 10,114.4 min).