DISTRIBUTION AND MOVEMENT OF JUVENILE SALMON IN BROWNLEE 



RESERVOIR, 1962-65 



BY JOSEPH T. DURKIN, DONN L. PARK, AND ROBERT F. RALEIGH, FISHERY BIOLOGISTS 

 BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 

 SEATTLE, WASH. 98102 



ABSTRACT 



Juvenile salmon — chinook {Oncorhynchus tshawy- 

 tscha), coho (O. kisutch). and sockeye and kokanee 

 (O. nerka) — were studied. Their rates and direction of 

 movement, spatial distribution, and successful passage 

 to the outlet varied in relation to surface currents, 

 water temperature, and dissolved oxygen concen- 

 trations. 



Some juvenile salmon stayed in Brownlee Reservoir 

 through the summer, fall, and early winter; the per- 

 centage varied between years. The percentages were 

 highest in years with high water level and retarded, 

 disoriented flows during the spring migration. Salmon 



Figure 1. — Brownlee Reservdir, Snake River, and major 

 tributaries. 



Published April 1970. 



FISHERY BULLETIN: VOL. 68, NO. 2 



that held over eventually concentrated in rather re- 

 stricted areas of the reservoir through the summer and 

 early fall, owing to high epilimnion temperatures and 

 to low concentrations of dissolved oxygen that extended 

 into the epilimnion from the hypolimnion. 



When the water level was low and reservoir currents 

 were oriented downstream, loss of orientation by 

 juvenile salmon was least and movement through the 

 reservoir was most rapid. These reservoir conditions 

 varied, but salmon populations that migrated early In 

 the year were most likely to encounter them. 



The completion in 1958 of Brownlee Dam on the 

 middle Snake River (Soule, Heikes, Mitchell, and 

 Schaufelberger, 1959) created a long, narrow res- 

 ervoir along the path of migrating Pacific salmon 

 (genus Oncorhynclms) and anadromous rainbow 

 trout (steelhead) Sahno gairdneri (fig. 1). At full 

 pool the impoundment is 92 km. long, less than 

 0.8 km. wide, and nearly 92 m. deep. The upper 

 24-km. of the reservoir is relatively shallow, slow 

 moving, and forms a river-run impoundment. The 

 lower 68 Ian., which thermally stratifies, lies 

 within an arid mountainous terrain. Powder River 

 Arm, a prominent appendage on the Oregon side, 

 joins the reservoir 17 km. above the dam and 

 extends westward for 15 km. The upper 5 km. of 

 the arm forms a wide, shallow, unstratified pond 

 when the reservoir is full. Juvenile salmon enter 

 the reservoir from the Snake and Powder Rivers 

 en route to the sea. 



When Brownlee Reservoir was completed, de- 

 tailed knowledge was lacking on the passage of 

 Pacific salmon and steelhead trout through large 

 resorvoii-s; therefore, BCF (Bureau of Coimner- 

 cial Fisheries) conducted detailed research at 

 Brownlee in 1962-65. Tliese studies covered native 

 stocks of steelhead trout, spring and fall chinook 

 salmon {0. tshaioytscha) , and kokanee (land- 

 locked sockeye salmon, 0. nerka) in addition to 



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