hatchery-reared fall chinook, sockeye, and coho 

 {0. kisutch) salmon. The research, which began 

 in the spring of 1962, consisted of five studies : (1) 

 limnology of the reservoir system (Ebel and 

 Koski, 1968), (2) upstream migration of adult 

 chinook salmon through the reservoir (Trefethen 

 and Sutherland, 1968), (3) migration of juvenile 

 salmon and trout into the reservoir (Krcma and 

 Raleigh, 1970), (4) distribution and movement of 

 juvenile salmon in the reservoir (this report), and 

 (5) migration of juvenile salmon and trout from 

 the reservoir (Sims, 1970) . 



Our report gives an account of movements and 

 distributions of the juvenile salmon in relation to 

 their environment. Data on the movements of 

 juvenile st«elhead trout were difficult to analyze 

 and report, as we were unable to clearly distin- 

 guish them from the nonanadromous wild and 

 hatchery-reared rainbow trout that were also in 

 the reservoir. 



EQUIPMENT AND PROCEDURES 



To obtain the desired information, it was neces- 

 sary to sample the juvenile fish in the lower 68 km. 

 of the reservoir. This sampling involved both gear 

 and marking efforts. 



FISHING EQUIPMENT 



Studies had indicated that four types of fishing 

 equipment were needed to capture juvenile fish : 

 floating traps, gill nets, purse seines, and two-boat 

 trawls. These, together with the fingerling col- 

 lection facility (skimmer net) of the Idaho Power 

 Company 1.5 km. above the dam, provided basic 

 data on the movement of juvenile salmon within 

 the reservoir. The sampling equipment was de- 

 ployed to intercept migrants in the upper, middle, 

 and lower reservoir from early in the year until 

 late fall (fig. 2). 



Floating Traps 



Floating traps were the most effective fishing 

 gear for capturing age-group salmon (fig. 3). 

 The dimensions of the trap, mesh size, and fishing 

 methods were similar to those described by Roth- 

 fus, Erho, Hamilton, and Remington.' From one 



' Lloyd O. Rothfus, Michael Erho, J. A. R. Hamilton, and Jack 

 D. Remington. 1964. A study of reservoir rearinR of coho salmon 

 in Lake Merwin, Washington. State Wash. Dcp. Fish., Res. Div., 

 18 pp. (Processed.) 



to seven of these units were used. The traps were 

 tended every other day early in the year and each 

 day between mid-March and early July. There- 

 after, as fish became less available, the traps were 

 operated with diminishing frequency and in most 

 years were removed by late July. 



Gill Nets 



The number of gill net stations fished depended 

 on the water level and its effect on the length of the 

 reservoir. At each site, two or three parallel sec- 

 tions of multifilament net, 30 m. long by 4.5 m. 

 deep, were fished at predetermined depths in a 

 manner similar to that described by Rees (1957). 

 The mesh sizes were 1.9, 2.5, 3.1, 3.8, 5.1, and 6.3 cm. 

 stretched mesh, of which the 2.5- to 3.8-cm. sizes 

 were most effective. The nets were most efficient on 

 salmon over 90 mm. fork length and at night. 



Purse Seines 



Two purse seines (Durkdn and Park, 1967) were 

 used as mobile sampling gear on fish concentra- 

 tions throughout the limnetic environment of the 

 reservoir. One of the seines was 180 m. long and 

 10.5 m. deep; the other was 210 m. long and 16.5 

 deep. Both were set from a barge. Purse seines 

 were used in the main resei-voir during spring and 

 early summer and in the Powder River Arm dur- 

 ing fall. 



Two-Boat Trawls 



Surface trawls (Johnson, 1956) were used to 

 locate concentrations of salmon and to determine 

 their relative abundance. The trawls were 3.0 m. 

 high, 5.4 m. wide at the mouth, and 7.8 m. long. 



MARKING 



Various types of marks were placed on captured 

 juvenile fish for identification at recapture. The 

 type of mark depended on the size of fish. Fish less 

 than 100 mm. long were marked with vinyl thread 

 tags (developed by personnel of the Fish Ommis- 

 sioii of Oregon). A jaw tag clamped to the left 

 mandible marked the fish (100 to 250 mm. long) ; 

 fish over 250 mm. had a plastic dart tag. Color 

 coded tattoos, used in 1962, were discontinued 

 when the vinyl thread tag became available. Other 

 groups of fish were marked by clipping fins before 

 they entered the reservoir (Krcma and Raleigh, 

 1970). 



220 



U.S. FISH AND WILDLIFE SERVICE 



