Fall chinook salmon spawning in the tailraces of lower Snake River hydroelectric projects

We conducted studies from 1993 to 1997 to identify and characterize potenti al spawning habitat of "endangered" fall chinook salmon Oncorhynchus tshawy tscha in areas downstream of four Snake River dams. This information was ne eded to provide guidelines for future operation of the lower Snake River hy droelectric system, including assessment of reservoir drawdown, and for sit e-specific construction planning. We used Geographic information System map ping technology to direct our initial search efforts. Suitable spawning hab itat was defined based on physical habitat characteristics of the tailrace areas. Redd surveys were conducted in primary search areas and planned cons truction sites from mid-November through December with an underwater Video system. The survey path and redd locations were mapped by using a Global Po sitioning System. During the 4-year study, fall chinook salmon redds were f ound in the tailrace downstream of Lower Granite (LGR), Little Goose (LGO), and Ice Harbor (TK) dams. The redds were the first verified sightings of s almon spawning at their locations since these dams were constructed in 1970 , 1975, and 1972, respectively. The total area used for spawning was about 2,560 m(2) for the LGR site and 580 m(2) for the LGO site. Only one redd wa s found downstream of the IPI project. Redds were in water from 4.0 to 8.1 m deep and on cobble substrate. All redds were adjacent to the outfall Row from juvenile fish bypass systems and on the powerhouse side of the river. Although temporal use was variable among individual projects, within-site f idelity was high. Tailrace spawning accounted for about 12% of the redds in the main stem of the Snake River during 1993 and 1994 but declined to less than 5% in 1996 and 1997.