Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 6569
Title: Evaluation of juvenile salmonid survival through the second powerhouse turbines and downstream migrant bypass system at Bonneville Dam, 1987
Author/Editor: Earl M. Dawley, Lyle G. Gilbreath, Richard D. Ledgerwood
Publication Year: 1988
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: DACW57-87-F-0323
Pages: 47
Date: 01/01/1988

In 1987, the National Marine Fisheries Service, in cooperation with the U.S. Army Corps of Engineers, began a multi-year study to evaluate survival of subyearling fall chinook salmon passing through the Bonneville Dam Second Powerhouse turbines, bypass system, and spillway.  Research conducted in 1987 had the following objectives:
(1)  Determine short-term comparative survival of juvenile salmon released at upper and lower locations in a Second Powerhouse turbine intake; in the Second Powerhouse bypass system; and below Bonneville Dam at Hamilton Island (rkm 232).  Estimates are to be obtained from brand recoveries in the estuary at Jones Beach (rkm 75).
(2)  Determine the long-term survival (to adults) of marked subyearling chinook salmon released at the locations listed in objective 1.  Estimates are to be obtained from tag and brand recoveries in various fisheries, at the Bonneville Dam fishtrap, and at hatcheries.

In estuarine sampling, the lower recovery rates for control and bypass­released fish vs. turbine-released fish caused serious concern about release sites, release procedures, and unidentified hazards in migration routes.  By releasing the control group of fish 2.5 km downstream from Bonneville Dam at Hamilton Island, we anticipated high survival because this group of fish would be unaffected by the dam complex and by predators inhabiting the adjacent areas.  Theoretically, differences in recovery rates between control and treatment groups would represent the impact of the treatment on survival. Instead, apparently, one or more unexpected factors overshadowed the possible impact of turbine-related mortality on test fish.

We also anticipated relatively high survival for the bypass treatment groups because these fish do not pass through the turbines.  We assumed that there would be increased mortality of fish passing through the turbines.  This project-related mortality cannot now be assessed because of the apparent greater mortality of control and bypass fish.

We hypothesize that control fish released on the shoreline at Hamilton Island were subjected to more predation than were groups released in mid-river.  Previous observations of similar juvenile fall chinook salmon from estuarine sampling suggest that shoreline migration is likely for:  1) fish recently released from a hatchery; 2) small fish; and 3) non-smolted fish.

We assume that fish released in mid-river traveled some distance downstream before establishing shoreline migration behavior, and that the mid-river portion of their migration produced less contact with predators than the shoreline route probably taken by the control fish. A mid-river release site for control fish will be established for next year.