EMIGRATION OF JUVENILE SALMON AND TROUT FROM BROWNLEE 



RESERVOIR, 1963-65 



BY CARL W. SIMS, FISHERY BIOLOGIST 



BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 



SEATTLE, WASH. 98102 



ABSTRACT 



Floating scoop traps below Brownlee Dam captured 

 samples of marked and unmarked salmon and trout 

 that had left the impoundment from July 1963 through 

 August 1%5; estimates of emigration were based on 

 these samples. 



Success of passage varied among years and popula- 



tions and was affected by the environment in the 

 reservoir during outmigration. Downstream migrants 

 that entered the reservoir early in the season were more 

 successful than those that entered later. Emigration 

 was also more successful when the reservoir level was 

 low. 



Brownlee Reservoir was chosen for an extensive 

 research program by BCF (Bureau of Commercial 

 Fisheries) to determine how a large impoundment 

 affects the passage of salmon and trout. The 

 research, begun in the spring of 1962, consisted 

 of five studies: (1) limnology of the reservoir 

 system (Ebel and Koski, 1968); (2) upstream 

 migration of adult chinook salmon (Oncorhynchus 

 tshawytscha) through the reservoir (Trefethen and 

 Sutherland, 1968); (3) migration of juvenile salm- 

 on and trout into the reservoir (Krcma and 

 Raleigh, 1970); (4) distribution and movement of 

 juvenile salmon in the reservoir (Durkin, Park, 

 and Raleigh, 1970); and (5) migration of juvenile 

 salmon and trout from the reservoir (the present 

 report) . 



Brownlee Reservoir, on the middle Snake River, 

 lies at the southern end of Hells Canyon along the 

 border between northeast Oregon and western 

 Idaho. The reservoir is about 92 km. long and 

 averages slightly less than 800 m. wide. Brownlee 

 Dam (constructed by the Idaho Power Company) 

 is a high-head structure, the primary function of 

 which is hydroelectric power production. It is 

 396 m. wide on the top, has a single spillway and 

 four Francis turbines with vertical shafts, and 

 creates 83 m. of head at full pool. The dam dis- 

 charges directly into Oxbow Reservoir, formed by 

 Oxbow Dam about 19 km. downstream. 



In an attempt to provide facilities for the passage 

 of juvenile salmon and trout past Brownlee Dam, 



Published April 1970. 



FISHERY BULLETIN: VOL. 68. NO. 2 



the Idaho Power Company installed a fingerHng- 

 collection system in 1959 in the forebay of the 

 reservoir about 3 km. downstream from the dam 

 (Soule, Heikes, Mitchell, and Schaufelberger, 

 1959). The system, consisting of a shore-to-shore 

 barrier net and surface collection traps, proved 

 only partly successful.' Many fingerlings passed 

 under or through the barrier net and left the 

 reservoir via the turbines or spillway. Idaho 

 Power Company removed the system in February 

 1964, after which all fish that left the reservoir 

 passed through the turbines or spillway. 



Native populations of anadromous salmon and 

 trout affected by Brownlee Reservoir include fall- 

 and spring-run chinook salmon {Oncorhynchus 

 tshawytscha) and steelhead trout (Salmo gairdneri) . 

 Before the construction of Brownlee Dam in 1958, 

 the largest population was fall-run chinook salmon, 

 which spawned in the Snake River upstream from 

 what is now the upper end of Brownlee Reservoir. 

 The Fish Commission of Oregon estimated annual 

 fall chinook salmon spawning runs of as many as 

 20,000 fish in the late 1950's. By 1963 this popula- 

 tion was greatly reduced. Before 1963, spring-run 

 chinook salmon spawned in the Weiser River (a 

 tributary of the Snake River above the head of 

 the reservoir) and in Eagle Creek (a tributary of 

 the Powder River, which enters near the lower 

 end of the reservoir). Steelhead trout were native 

 to Weiser River and Eagle Creek as well as several 



' Oraben, James E. 1964. Evaluation of fish facilities, Brownlee and Oibow 

 Dams, Snake River. Idaho Department of Fish and Game, Boise, Idaho, 

 60 pp. (Processed.) 



245 



