12 3 4 12 3 4 

 MARCH APRIL 



Figure 10. — Timing of migration of juvenile hatchery- 

 reared fall Chinook salmon (age-group 0) to Brownlee 

 Reservoir from the Snake River, 1964r-65. 



the reservoir. These fish were reared from eggs 

 obtained in the fall of 1963 from Babine Lake, 

 British Columbia. The eggs were eyed at a 

 hatchery at Mavirice Lake, British Columbia, and 

 transpoi'ted to Leavenworth National Fish Hatch- 

 ery in Washington, wliere they were reared until 

 their release in 1965. Releases of 20,000 to 30,000 

 fish were made 5 days each week from March 15 

 to April 8, 1965; river water temperatures aver- 

 aged 9.8° C. The sockeye salmon moved rapidly 

 downstream; the first migrants were recovered 

 within 2 days after the initial release. Peak migra- 

 tion was during the first week of April (fig. 12) ; 

 by mid-April the migration was nearly complete. 

 Sockeye salmon migrants averaged 121 mm. long 

 (86-175 mm.). 



UPSTREAM MOVEMENTS OF JUVENILE 

 CHINOOK SALMON 



A late group of chinook salmon fingerlings ap- 

 peared at the Snake River trap near the end of 

 June or in early July of each year. Because the 

 migrations of fall- and spring-run chinook salmon 

 were essentially completed by this time, the origin 

 of these fish was of interest. Their length was 

 similar to that of age-group I fish from the Weiser 

 River, but examination of their scales revealed 

 tliat they were fingerlings of age-groups O and I. 

 Growth patterns on their scales showed an area 

 of rapid growth at the margin typical of fish from 



12 3 4 

 APRIL 



I 2 3 

 JUNE 



Figure 11. — Timing of migration of juvenile hatchery- 

 reared coho salmon from the Snake River to Brownlee 

 Reservoir, 1964. 



the reservoir. This scale structure indicated they 

 had moved upstream from the reservoir. This 

 movement was confirmed in 1963 when 12 fin- 

 clipped individuals were caught that had been 

 marked as emigrants from Eagle Creek in the 

 fall of 1962. In 1964, 2.7 percent of the fish cap- 

 tured from this July migration were fall chinook 

 salmon that had been previously tagged and re- 

 leased in the upper reservoir. 



According to Durkin et al. ( 1970) , this upstream 

 movement of fish into the Snake River may be 

 related to the environment of the reservoir. The 

 reservoir was rapidly filled early in the 1963 sea- 

 son, and, excejjt for a minor drawdown of 3 m. 

 in May, it was at full pool. Some Eagle Creek fish 

 moved up the reservoir in 1963, possibly because 

 surface currents frequently moved toward the up- 

 stream end of the reservoir. Late arrivals may 

 have been attracted upriver by the relatively 

 cooler, oxygenated water as the smolting phenom- 

 enon (Hoar, 1963; Conte, "Wagner, Fessler, and 

 Gnose, 1966) attenuated and reservoir tempera- 

 ture and oxygen conditions deteriorated (Ebel 

 and Koski, 1968). As the river temperature in- 

 creased to 20° C, the fisli returned to the reser- 

 voir. In 1964, when the surface level of the 

 reservoir was lower, Eagle Creek fish were not 

 captured in the Snake River: however, recovery 

 of fall chinook salmon that had been marked and 

 released in the upper reservoir again suggested an 

 upstream response to cooler water. 



JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR 



213 



