Estimating the daily passage of juvenile salmonids at McNary Dam on the Columbia River

The U.S. National Marine Fisheries Service, under contract to the U.S. Army Corps of Engineers, monitored the seaward migration of juvenile salmonids through the Snake-Columbia river system from 1973 to 1983. We developed a procedure for estimating the numbers of steelhead Salmo gairdneri and yearling chinook salmon Oncorhynchus tshawytscha smolts passing McNary Dam each day in 1982-1983. The method utilized the fingerling collection and bypass system contained within the powerhouse. Freeze-branded groups of smolts released upstream from the dam were used to calibrate the efficiency with which migrants were collected over a range of powerhouse discharge levels. Application of collection efficiency calibration curves enables researchers and fisheries managers to generate daily estimates of smolt passage as a function of the amount of water discharged through the powerhouse and the number of fish collected in the bypass system