NOTE Giorgi et al.: Migratory characteristics of juvenile Oncorhynchus tshawytscha 



873 



Developing water management strategies to ben- 

 efit the juvenile stages of ocean-type chinook salmon 

 has become an important issue in the Pacific North- 

 west; however, basic information describing migra- 

 tory characteristics is required before such strate- 

 gies can be designed. We undertook the present in- 

 vestigation to describe the migratory characteristics 

 of ocean-type chinook salmon in John Day Reservoir, 

 a major impoundment on the Columbia River. This 

 paper describes the movement and residence time of 

 zero-age ocean-type chinook salmon within the res- 

 ervoir and examines the relationship between mi- 

 gration time through the reservoir and key environ- 

 mental variables. 



Study area 



John Day Dam is a hydroelectric project on the Co- 

 lumbia River at river kilometer (rkm) 345, approxi- 

 mately 200 km east of Portland, Oregon (Fig. 1). The 

 project was constructed and is operated by the U.S. 

 Army Corps of Engineers (COE). The John Day Res- 

 ervoir is the largest impoundment on the river, ex- 

 tending 122 km upstream to the tailrace of McNary 

 Dam, located approximately 52 km downstream from 

 the confluence of the Columbia and Snake rivers. The 

 width of the reservoir ranges from 0.8 to 4.2 km, and 

 its mid-pool depth extends to 48 m. The dam is ap- 



proximately 1 km in length and is currently fitted 

 with 16 turbines. 



Methods 



Migrant zero-age chinook salmon entering the juve- 

 nile fish sampling facilities at McNary Dam were 

 collected from mid-June through August 1981 

 through 1983. The fish were predominantly a mix- 

 ture of fall and summer races (named for the time of 

 adult returns) from the Columbia River and some 

 small portion of fall races from the Snake River. The 

 yearling chinook migration peaks during May at 

 McNary Dam but can extend from April into June 

 (FPC 4 ). By mid-June more than 95% of the yearlings 

 have passed the dam. During late June some year- 

 lings remain mixed with the zero-age migrants. To 

 minimize the inclusion of the larger yearlings in our 

 experimental groups we used fish less than 110-mm 

 fork length during June. Each week, up to three 

 groups of fish were freeze branded with a unique 

 mark (Mighell, 1969). All fish bearing the same brand 

 were released into the tailrace below McNary Dam 

 at 2100 h on their respective release dates to con- 

 tinue their downstream migration. 



4 Fish Passage Center. 1992. Fish Passage Center 1991 Annual 

 Report. Columbia Basin Fish and Wildlife Authority, Portland. 

 OR, 52 p. 



