APRIL 



Cotches 

 N= 2,412 I I ADO»e reservoir 

 N- 281 SS Skimmer net 



neor dam 



a1 



Cotches 

 N= 15,000 I I Above reservoir 

 N= 620 ^J Sliimmer net 

 near dam 



a R 



JUNE 



JULY 



Figure 8. — -Percentages of the total catch of juvenile spring chinook salmon from Weiser 

 River, taken during different weeks at the upper and lower ends of Brownlee Reservoir, 

 1962-63. 



outmigration did not occur until after the first 

 of the year (Sims, 1970). Tliere were two major 

 migrations of Eagle Creek fish from the reservoir 

 each year; the first consisted of fish that entered 

 the reservoir in the fall and overwintered, and 

 the second consisted of spring migrants that moved 

 directly from the stream to the dam (fig. 10). The 

 first group migrated from the reservoir primarily 

 from late January to April and the second group 

 from late March to June ( fig. 11 ) . 



We investigated the possibility that the reservoir 

 might be delaying the seaward migration of the 

 fall migrants. Tagging data showed that most fall 

 migrants spent about 3 months in the reservoir, 

 whereas most spring migrants moved through the 

 reservoir in a much shorter time. In 1964 and 1965, 

 groups of Eagle Creek fall migrants were marked, 

 transported around Brownlee and Oxbow Dams, 

 and released in the Snake River. Sampling at Ice 

 Harbor Dam (442 km. downstream from Brown- 

 lee) showed that fish released in the river below 

 the dams overwintered in the Snake River and 

 arrived at Ice Harbor Dam at about the same time 



as the group that passed through the reservoir.^ It 

 appears, therefore, that Brownlee Reservoir did 

 not unduly delay the fall migration from Eagle 

 Creek and tliat these fish nonnally overwinter be- 

 fore going to sea. 



Although Brownlee Reservoir did not appear 

 to cause an appreciable delay in the seaward mi- 

 gration of the fall migrants, some fish from Eagle 

 Creek became disoriented in the reserv'oir imder 

 certain conditions. In 1962 and 1964, fish from 

 Eagle Creek moved consistently downstream to- 

 ward the dam. In 1963, however, a segment of the 

 population moved upreservoir. This movement 

 was proven by capture of 12 marked individuals 

 in the Snake River 4 km. above the reservoir in 

 late June and July 1963. Drawdown of the reser- 

 voir exceeded 14 m. in 1962 and 1964 but was only 

 6.4 m. in 1963. Figures 4 and 5 indicate that these 

 conditions would provide weak downstream cur- 

 rents in 1962 and 1964 but disoriented curi-ents in 



' Personal communication, Howard Raymond, Fishery. Biol- 

 ogist, BCF Biological Laboratory, Seattle, Wash,, June 1065. 



230 



U.S. FISH AND WILDLIFE SERVICE 



