FALL CHINOOK SALMON OF AGE-GROUP 



Hatchery- reared fall chinook salmon were re- 

 leased in the Snake River about 120 km. above 

 Brownlee Reservoir in March 1964 and 1965. Al- 

 though released over a period of only 10 days, their 

 movement into the reservoir extended over 3 

 months. Early and late migrants were 46 mm. and 

 130 mm. long in 1964 and 67 mm. and 135 mm. in 

 1965. 



In 1964 and 1965, tagged hatchery chinook 

 salmon moved primarily toward the dam until 

 mid-May. After mid-May in 1964, some tagged 

 fish were recaptured moving upreservoir; four 

 tagged fish were recaptured in traps in the Snake 

 River about 4 km. upstream from the head of the 

 reservoir (Krcma and Raleigh, 1970). This up- 

 stream movement involved fewer fish in 1965. 

 According to Sims (1970), 50 percent of the esti- 

 mated migration of hat^heiy-reared chinook salm- 

 on into Brownlee Reservoir had left by the end 

 of June 1964 and over 97 percent in 1965. 



The movement upstream into the Snake River 

 in 1964 might have been related to temperature, 

 as noted previously for populations of native juve- 

 nile chinook salmon. 



The ability of these fish to move through the 

 reservoir to the river below Brownlee Dam (50 

 percent in 1964 and 97 percent in 1965) appeared 

 to vary with volume of flow, direction of current, 

 and length of reservoir. The drawdown lasted 6 

 weeks longer in 1965 than in 1964 and was accom- 

 panied by spillway discharges of large volume and 

 duration and high volumes of inflow from the 

 Snake River (fig. 4). During the 1965 migration 

 this condition produced not only a smaller im- 

 poundment (45-50 km. long) but currents of 

 higher velocity that were more consistently toward 

 the dam than in 1964. 



The rate of movement of tagged chinook salm- 

 on in the reservoir was similar in 1964 and 1965 

 even though the enviromnents were different. The 

 rate for all chinook salmon that moved toward 



the outlet averaged 3.0 and 2.9 km./day, respec- 

 tively (table 4) . Fish tagged through the first half 

 of May generally moved faster than those tagged 

 later. Upreservoir movement for nine chinook 

 salmon averaged 0.89 km./day in 1964 and 2.0 

 km./day in 1965. 



Chinook salmon recaptured downriver at Ice 

 Harbor Dam averaged 19.9 kmyday in 1964 and 

 18.8 km./day in 1965 through the reservoir and 

 river. 



Fish captured early in the season in midreser- 

 voir and along both banks indicated that fall 

 chinook salmon of age-group O were distributed 

 throughout the surface area. Gill net catches 

 showed that juvenile chinook salmon moved both 

 up and down the reservoir during darkness. This 

 observation implies that most directed movement 

 may have occurred during daylight and that 

 fish milled or were carried by currents during 

 darkness. 



The distribution of hatchery-reared fall chinook 

 salmon through the summer was similar to that 

 of native fall chinook salmon (fig. 16). In the 

 spring the fish were generally distributed through- 

 out the epilimnion of the reservoir. As the surface 

 temperature increased the fish moved into deeper 

 water and downreservoir. Temperatures above 

 21° C. at the surface and low oxygen concentra- 

 tions (less than 3 p.p.m.) at depths where the 

 water was cooler forced the fish to move into re- 

 stricted areas. The increased catches of fish in gill 

 nets in the upper reservoir in Jime and July were 

 probably the result of fish returning from a tem- 

 porary upstream movement into the Snake River. 



Some hatchery-reared chinook salmon from the 

 1964 release remained in Brownlee Reservoir dur- 

 ing the winter. Sims (1970) estimated that only 

 about 85 percent of the hatchery-reared fall chi- 

 nook salmon that entered the reservoir in 1964 

 migrated out that year. Also 17 fish from this 

 group were captured in the reservoir in February 

 and March 1965. 



Table 4. — Summary of direction and rale of movement of tagged age-group O hatchery-reared fall chinook salmon in Brownlee 



Reservoir, 1964-6S 



238 



U.S. FISH AND WILDLIFE SERVICE 



