gation. A small hatchery for fall chinook sal- 

 mon (0. tshawytscha) , 1 km. downstream from 

 the trapping site, has been operated at Oxbow 

 Dam from 1960 to the present by the Idaho 

 Fish and Game Department. 



Fishery agencies recognized that Brownlee 

 Reservoir posed a number of problems. The 

 impoundment is 92.5 km. long; it has almost no 

 current except during periods of high river 

 discharge and extreme drawdown ; water tem- 

 peratures are high and oxygen concentrations 

 are low during summer and early fail when 

 spawning migrations occur. 



To learn if adults could pass successfully 

 through Brownlee Reservoir and reach the 

 spawning grounds, the Idaho Fish and Game 

 Department tagged fall chinook salmon (with 

 Petersen disk tags) in 1960-61. The Bureau 

 of Commercial Fisheries, in cooperation with 

 Idaho, continued the investigations in 1962. 

 Petersen disk tags were used in all years; the 

 Bureau also used sonic tags in 1961-62 to trace 

 the orientation and movement of fish. 



This report summarizes the results of the 

 1960-62 studies. It also contains information 

 on (1) orientation and migratory behavior of 

 sonic-tagged salmon, (2) observations of totally 

 spent fish in the Snake River above Brownlee 

 Reservoir, and (3) use of tributary spawning 

 streams after completion of Brownlee Reser- 

 voir. 



METHODS AND MATERIALS 



The general plan was to capture adult chi- 

 nook salmon in a trap at Oxbow Dam and trans- 

 port them upstream for release either in 

 Brownlee Reservoir or in the Snake River 

 above the reservoir (fig. 1). Some of the fish 

 released in the reservoir were either tagged or 

 fin clipped ; others were caught and released un- 

 marked without additional handling. The 

 relative numbers recovered on ancestral spawn- 

 ing grounds below Swan Falls provided data 

 that enabled us to measure the ability of mi- 

 grants to pass through Brownlee Reservoir. 

 Sonic tags were applied to 59 fish in 1961-62 

 to obtain information on orientation and mi- 

 gratory behavior in and above the impound- 

 ment. A summary of data on tagging and 

 release is shown in table 1. 



r.AITlJKK AND HANDLING 



Adult chinook salmon used in the experi- 

 ments were taken at different stages of the 

 spawning run in the different years. In 1960 

 and 1961 the fish were obtained after the peak 

 of the run. Hauck (1961)', describing the 

 work in 1960, mentioned ". . . that the selection 

 of fish for tagging was not on a random basis ; 

 that some selection was made for better fish on 

 the basis of appearance and physical vigor." 



1 Hauck, Forrest. 1961. Fall chinook salmon tagging studies, Snake 

 River, 1960. Idaho Fish and Game Dept.. 7 pp. (Processed.] 



Table 1. — Summarii of data vn. tmiqiiuj and release duritiq tests on passage of fall-run chinook salmon through Brownlee Reservoir. 



19G0-62 



{Unmarked fish were released in the reserooir during normal transport to maintain run; all fish u-ere taken from Ira/i at Oxhow Dam. {fig. 1)] 



Anesthetized for tapging, but not during transport to release site. 



36 



U.S. FISH AND WILDLIFE SERVICE 



