Falls — but fish could readily pass these except in 

 periods of extremely low riverflow. Cascade 

 Rapids was inundated by Bonneville Dam in 

 1938; Celilo Falls by The Dalles Dam in 1957. 



Each year Pacific salmon, Oncorhynchus spp., 

 and steelhead trout, Salmo gairdneri, that spawn 

 above Bonneville Dam yield several million dollars 

 to commercial and sport fisheries in the river and 

 ocean. Because of the great value of these fish, it 

 is important to ensure that they pass over the 

 dam with a minimum of loss and delay. 



Hanson, Zimmer, and Donaldson (1950) 

 counted many dead fish in the river below Bonne- 

 ville Dam in various seasons and years, and fisher- 

 men in boats below the dam often observed 

 floating dead fish or dying fish on the surface. 

 Chinook salmon were reported most frequently, 

 but other species were also noted: sockeye or 

 Columbia River blueback salmon, 0. nerka; steel- 

 head trout; American shad, Alosa sapidissima; 



white sturgeon, Acipenser transmontanus; carp, 

 Cyprinus carpio; and Pacific lamprey, Ento- 

 sphenus tridentatus. Biologists and fishermen sus- 

 pected that many of these fish died from attempt- 

 ing to find a route over the dam or from being 

 swept downstream through the spillway after 

 ascending a series of gravity-flow fish ladders, 

 the principal means for fish to migrate over the 

 dam. Although many of the fish seemed to nego- 

 tiate the ladders satisfactorily, Schoning and 

 Johnson (1956) estimated that chinook salmon 

 were delayed an average of 2.6 to 3.0 days in 

 their migration. 



This paper reports a study of the magnitude 

 and possible causes of the mortality of fish at 

 Bonneville Dam, with particular reference to the 

 summer run of chinook salmon, which is believed 

 to be more adversely affected than other runs. 



Bonneville Dam (fig. 1) consists of two con- 

 crete sections — the spillway and the powerhouse — 



Figure 1. — Bonneville Dam, showing the spillway and powerhouse sections and the difference in turbulence between 

 the two sections. Photo taken April 29, 1958, when spillway flow was 4,000 c.m.s. and powerhouse flow, 2,700 

 c.m.s. (Photo courtesy of U.S. Army Corps of Engineers.) 



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U.S. FISH AND WILDLIFE SERVICE 



