and 1965. In 1964, 2,100 kokanee fingerlings 

 (1963 year class) were estimated to have left the 

 reservoir, representing about 38 percent of the 

 estimated recruitment to the reservoir (table 9). 

 The outmigration started during the latter part of 

 June 1964, reached a peak in early August, and 

 ended by the first week in September. 



Table 9. — Estimated immigration of juvenile kokanee into 

 Brownlee Reservoir from the Snake River system and esti- 

 mated emigration from the Reservoir, May 1964. and 1966 



An estimated half million age-group I kokanee 

 entered Brownlee Reservoir in 1965, but only 10 

 percent (52,100 fish) are estimated to have 

 left the reservoir. According to Durkin et al. 

 (1970), the poor success of the migration of 

 kokanee can be attributed to the high reservoir 

 level and its attendant lack of downstream- 

 orienting currents. These fish did not enter the 

 reservoir until June and did not begin to leave 

 until late June. The outmigration was greatest in 



late August and was completed by early Septem- 

 ber (fig. 5) . Fish remaining in the reservoir in late 

 July, August, and September were subjected to 

 high temperatures in the epilimnion (above 21" 

 C.) and oxygen-deficient water in the hypolim- 

 nion. These factors forced fish into unfavorable 

 habitats where survival was poor (Durkin et al., 

 1970). 



EMIGRATION OF JUVENILE HATCHERY-REARED 

 SALMON 



About 250,000 age-group juvenile fall chinook 

 salmon and 375,000 age I juvenile coho salmon 

 were released in the Snake River above Brownlee 

 Reservoir in late mnter and early spring of 1964. 

 Additional releases of 592,000 age-group fall 

 chinook salmon and 473,000 age-group I juvenile 

 sockeye salmon were made in the spring of 1965. 

 Chinook and coho salmon fingerlings were from 

 hatcheries on the lower Colimabia River; sockeye 

 salmon fingerlings were from the Leavenworth 

 National Fish Hatchery, where they had been 

 reared from eggs obtained from Babine Lake in 

 British Columbia. 



Fall Chinook Salmon 



About 85 percent (94,500) of the estimated 

 111,500 hatchery-reared juvenile fall chinook 

 salmon that entered the reservoir in 1964 passed 



20 



tn 

 o 



z 



o 



5 10 



UJ 



z 



1 1 r 



Ldt 



T^^^ i'   ■!■ 1 1 1 r 



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



1964 



1965 



Figure 5. — Estimated emigration from Brownlee Reservoir of juvenile native kokanee from the Snake 



River system, 1964-65. 



252 



U.S. FISH AND WILDLIFE SERVICE 



