Figure 2. — FloaJting traps (migrant dippers) used to sample migrations of juvenile salmon and rainbow 

 trout in the Snake River above Brownlee Reservoir. 



fied by age group on the basis of lengths 

 determined by daily sampling. The length-age re- 

 lation was established by scale analysis. Finger- 

 lings in their first year of life are termed age- 

 group 0; these fish become age-group I on Janu- 

 ary 1 of the succeeding year. 



Marked fish were used to estimate the propor- 

 tion of the migration captured by the traps. The 

 proportion varied with trap design and position, 

 size and species of migrants, and flow and tur- 

 bidity of the river. A portion of the daily catcli 

 of fish was marked, transported 3.2 km. upstream, 

 and released for recapture. They were marked by 

 age group and released at scheduled intervals dur- 

 ing the day and night. 



Fish marked to assess the migration from the 

 Snake River were tattooed (Volz and "Wlieeler, 

 1966). This method provided many combinations 

 of marks that were durable and could be easily 

 detected. Juvenile salmon from each population 

 were fin-clipped or jaw-tagged each year for sub- 

 sequent identification as they moved through the 

 reservoir. 



EAGLE CREEK 



The sampling site at Eagle Creek was 183 m. 

 upstream from its confluence with the Powder 

 River and about 460 m. from the reservoir (fig. 1) . 

 The stream at this point was 15 m. wide at noiTnal 

 flows. Except during maximum ninoft' in the 

 spring, floAvs seldom exceeded 57 c.m.s. 



Samples of downstream migi'ants were obtained 

 with a stationary louver device (Bates and Vin- 

 sonhaler, 1057) — see figure 3. In 1962, the louver 

 (18.3 m. long and 0.9 m. high) was positioned at 

 a 30° angle to the stream bank. In 1963, to increase 

 the catch and eliminate selectivity for larger fish, 

 the angle was decreased to 15° and the length 

 extended to 36.6 m. In 1964, the channel was al- 

 tered above the louver to straighten the approach 

 flow. 



Fish from Eagle Creek were collected from 

 three sources and marked in a variety of ways. 

 Most fish were stained with Bismark Brown Y 

 dye^ (Deacon, 1961) and released above the sam- 



1 Trade names referred to In this publication do not imply 

 endorsement of commercial products by the Bureau of Com- 

 mercial Fisheries. 



JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR 



205 



