30 



20 



10 



30 - 



-20 



10 



;30 



o 20 



10 



30 - 



1962 



1963 



1964 



1965 



Figure 8. — Timing of migration of juvenile rainbow trout 

 to Brownlee Reservoir from the Snake River, 1962-65. 



Table 6. — Age groups and lengths of juvenile rainbow 

 trout captured in the migrant dipper traps in the Snake 

 River above Brounlee Reservoir in 1963 



Age group 



Fish 



Mean 

 length 



Range 



0... 

 I... 

 II.. 

 III. 

 IV.. 



1 Insufficient sample. 



Table 7. — Age groups and lengths of juvenile rainbow 

 trout from Eagle Creek during migration past sampling 

 site in fall 1962 



Age group 



Fish 



Mean 

 length 



Range 



0... 



I... 

 II.. 

 III- 



rv.. 



Fall Chinook Salmon 



Hatchery-reared juveniles of fall cliinook 

 salmon were released in the Snake River above 

 the re.sei-voir in 1964 and 1965 to supplement the 

 dwindling smolt migrations of wild fall chinook 

 salmon. About 250,000 fall chinook salmon were 

 released 120 km. above the reservoir from 

 March 30 to April 3, 1964, wlien water tempera- 

 tures averaged 9.5° C. In 1965, 592,000 juvenile fish 

 were released 88 km. upstream from tlie reservoir 

 from March 15 to 25, when the water temperature 

 averaged 9.8° C. A tank truck transported the 

 fish from hatcheries on the lower Columbia River. 

 Tlie fish were released during daylight. 



The migrations of liatchery chinook salmon 

 overlapped with migrations of wild spring chi- 

 nook (age-group I) from the Weiser River. In 

 1964, juvenile chinook salmon from hatchery re- 

 leases were recovered at the Snake River sampling 

 site within 3 days after the first release. Down- 

 stream migration continued until late June, but 

 catches were highest in mid-May (fig. 10). The 

 migration in 1965 was longer and the peak less well 

 defined. 



The lengths of hatchery-reared chinook salmon 

 increased as the season progressed and by late 

 April were the same size as those of the age-gi'oup 

 I wild chinook salmon from Weiser River. The 

 hatchery fisli captured at the migrant dipper in 

 1964 averaged 74 mm. (56-100 mm.) early in the 

 season and 112 mm. (91-135 mm.) near the end of 

 the migration (table 8). In 1965, the hatchery fish 

 averaged 69 mm. (46-90 mm.) at the start of 

 migration and 112 mm. (96-125 mm.) at the end. 



Table 8. — Lengths of hatchery-reared juvenile chinook 

 salmon during migration past sampling site in Snake 

 River, 1964-66 



' March through mid-May. 

 2 Mid-May through June. 



> Insufficient sample. 



Coho Salmon 



The introduction of 375,000 juvenile coho 

 salmon into the Snake River in 1964 provided an 



JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR 



211 



