Evaluation of Adult Fish Passage at Little Goose and Lower Granite Dams, 1981

Migratory movements of adult salmonids were studied from 20 April through 19 June 1981 to evaluate adult fish passage at Little Goose and Lower Granite Dams on the lower Snake River in southeastern Washington. Each fishway entrance was monitored with electronic fish detectors and chinook salmon (Oncorhynchus tshawytscha) were radio tracked in the projects\u27 tailraces and fishways. The most frequently used fishway entrances at Little Goose were the north shore and south shore entrances, which combined accounted for 65.3% of total net entries recorded by electronic detectors. At Lower Granite, the south shore entrance was the most heavily used on days without daytime spill discharges, while the north shore entrance was preferred on most spill days. The percentage of total entries at the north shore entrance increased with increasing spill levels up to 50 to 60 thousand cubic feet per second (kcfs), with use of the entrance tapering off again at higher spills. Radio tagged fish took about 1 to 1.5 days for passage at both projects during nonspill periods while up to 7.5 days were required to cross Lower Granite when spill discharges averaged above approximately 40 kcfs. Excessive delays during heavy spill were caused by fish holding downstream of the project and moving into areas on the north side of the navigation lock away from all fishway entrances. Spill occurred during the hours of data collection on 33 days of the 54 day research season at Lower Granite and on only 4 days at Little Goose, resulting in less information on spill effects on fish passage at Little Goose