Brownlee Dam in 1964 (table 10). These fish first 

 appeared at the traps below the dam in early 

 April (9 days after release in the Snake River 

 above the reservoir) and their numbers peaked in 

 the second week of May. Small numbers of fish 

 moved out of the reservoir through the summer 

 until the emigration of the 1964 year class was 

 completed on September 1 (fig. 6). 



An estimated 275,200 hatchery-reared fall 

 chinook salmon (1965 year class) left the impound- 

 ment in 1965 — more than were estimated to have 

 entered the reservoir. The discrepancy between 

 the two estimates is probably due to different 

 sampUng methods. Nevertheless, such a compari- 

 son is useful when one recognizes that the low 

 range emigration estimate (175,000 fish) is within 

 the 95-percent statistical confidence range of the 

 immigration estimate. Fish of the 1965 year class 

 were first taken in the scoop traps below the dam 

 in late March (fig. 6), 12 days after release in the 

 Snake River above the reservoir. Peak migration 

 was in mid-April, and a few fish were still leaving 

 the reservoir when the experiment terminated at 

 the end of August. 



Coho Salmon 



Emigration of juvenile hatchery-reared coho 

 salmon (1963 year class) in 1964 was estimated 

 at 51,600 fish or about 75 percent of immigration 

 to the reservoir (table 11). The emigration of 

 coho salmon began on May 16, 1964, about 6 weeks 



Table 10. — Estimated immigration of juvenile hatchery- 

 reared fall chinook salmon into Brownlee Reservoir from 

 the Snake River and estimated emigration from the 

 Reservoir, 1964-65 



' Disci«pancy between estimates of immigration and emigration probably 

 due to differences in sampling techniques in the Snake River and below 

 Brownlee Reservoir. 



after their release in the Snake River above the 

 reservoir. The run reached a peak 1 week later 

 and continued until the end of August (fig. 7). 



Sockeye Salmon 



Juvenile hatchery-reared sockeye salmon (1964 

 year class) released in 1965 had little difficulty 

 in passing through the reservoir. Emigration in 

 1965 was estimated at 408,000 fish, more than 

 100 percent of the estimated immigration (table 

 11). The range of the two estimates overlap, 

 however. The first sockeye salmon appeared in 

 the scoop traps 6 days after the first releases on 

 March 15, 1965. The emigration was relatively 

 short, beginning on March 21 and ending by the 

 second week of May (fig. 8) . Peak was during the 

 week of April 4 to 10, when 175,000 fish are 

 estimated to have left the reservoir. 



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APR MAY JUN. JUL. AUG. SEP OCT NOV. DEC. JAN. FEB. MAR. APR. MAY JUN. JUL. AUG.SEP 

 1964 1965 



Figure 6. — Estimated emigration from Brownlee Reservoir of juvenile hatchery-reared fall chinook 

 salmon from the Snake River, April 1964 to September 1965. 



JUVENILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR 



253 



