20 



z 

 < 

 m 



O 



X 



15 



5 10- 



5- 



"T~n->-p-r-,-^^ 



JAN. FEB MAR APR MAY JUN JUL 

 1964 



AUG SEP OCT NOV. DEC. 



Figure 7. — Estimated emigration from Brownlee Res- 

 ervoir of juvenile hatchery-reared coho salmon from 

 the Snake River, 1964. 



200 



5 150 

 o 



•a 100- 



50 



L 



— I 1 1 1 1 1 r 



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



1965 



Figure 8. — Estimated emigration from Brownlee Res- 

 ervoir of juvenile hatchery-reared sockeye salmon from 

 the Snake River, 1965. 



Table 11. — Estimated immigration of juvenile hatchery- 

 reared coho and sockeye salmon into Brownlee Reservoir 

 from the Snake River and estimated emigration from the 

 Reservoir, May 1, 1963 to August 31, 1965 



1 Discrepancy between estimates of ImmlgtBtlon and emigration probably 

 due to dlSerences In sampling techniques In Snake River and below Brownlee 

 Reservoir. 



EMIGRATION OF JUVENILE TROUT OF UNKNOWN 

 ORIGIN 



Because anadromous rainbow trout (steelhead) 

 could not be separated from native and hatchery- 

 reared resident rainbow trout, the data on emi- 

 gration include all populations of rainbow trout. 

 For the same reason, Krcma and Raleigh (1970) 

 did not attempt to estimate immigrations of rain- 

 bow steelhead trout. Comparisons of emigration 

 and immigration, therefore, were not possible. 

 Juvenile rainbow trout emigrated from Brownlee 

 Reservoir each year during this study. An esti- 

 mated 24,800 rainbow-steelhead trout (table 12) 

 left the reservoir from August 1963 through De- 

 cember 1964. The major emigrations were in 

 May and June. In 1965, emigration was esti- 

 mated at 73,600 fish, and the major outmigrations 

 were in April and May. 



Table 12. — Estimates of emigration of juvenile native and 

 hatchery-reared resident rainbow trout and anadromous 

 rainbow {steelhead) trout from Brownlee Reservoir, May 1, 

 1963, to August 31, 1966 



LENGTHS OF EMIGRANTS 



The sizes of the juvenile fish in various stocks 

 that emigrated from Brownlee Reservoir generally 

 increased as the season progressed. The fork 

 length of fall chinook salmon caught below the 

 dam from August 1963 through December 1964 

 was 45 to 240 mm. (table 13). Two distinct length 

 groups were evident from November 1963 through 

 June 1964. The larger fish (age-group I) were 

 from the 1963 year class of fall chinook salmon 

 from the Snake River; these fish dominated the 

 catch through March 1964. Beginning in April 

 1964, the smaller native spring chinook salmon 

 of the 1963 year class and the hatchery releases 

 of fall chinook salmon of the 1964 year class 

 dominated. Holdover of fish was slight in 1965; 

 the entire emigration was of native kokanee and 

 spring chinook salmon (age-group I) of the 1964 

 year classes and hatchery releases of sockeye 

 salmon (age-group I) and fall chinook salmon 

 (age-group 0) of the 1964 and 1965 year classes. 



Hatchery-reared coho salmon increased from 

 an average length of 125 mm. (90-155 mm.) in 

 May 1964 to 200 mm. (155-245 mm.) in August 

 1964 (fig. 9). 



254 



U.S. FISH AND WILDLIFE SERVICE 



