Seasonal and Diel Passage of Juvenile Salmonids at John Day Dam on the Columbia River

Abstract

-This paper documents the seasonal and diel movements of seaward-migrating juvenile Pacific salmonids Oncorhynchus spp. passing John Day Dam on the Columbia River. During the 1987–1989 and 1991–1993 seasons, the 10, 50, and 90% passage dates each fell within a 2-week period for yearling chinook salmon O. tshawytscha, steelhead O. mykiss, coho salmon O. kisutch, and sockeye salmon O. nerka. For subyearling chinook salmon, the 10 and 90% passage dates varied by as much as 1 month, although the median passage dates occurred within a 10-d period. The percentage of fish that passed at night (2200–0600 hours) averaged 80.7% for yearling chinook salmon, 75.7% for subyearling chinook salmon, 77.9% for steelhead, 88.6% for coho salmon, and 78.3% for sockeye salmon. Information concerning the hourly and seasonal movements of juvenile salmonids through hydroelectric dams are essential in making wise fisheries resource and river flow management decisions.