Northwest Fisheries Science Center

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Document Type: Report
Center: NWFSC
Document ID: 9261
Title: Utilization of Columbia River zooplankton by juvenile Chinook salmon
Author/Editor: Donovan R. Craddock, William D. Parente
Year: 1970
Institution: Technical Advisory Committee, Columbia River Thermal Effects Study. Bureau of Commercial Fisheries, Seattle Biological Laboratory

The seasonal abundance of zooplankton and their importance in the diet of juvenile chinook salmon in the Prescott-Kalama area of the Columbia River was studied in 1968-1969.  Sampling in the area of two proposed thermal electric plants showed that the Cladocerans Daphnia and Bosmina and a Cyclopoid copepod were the major zooplankters.  Peak abundance of the important zooplankters varied individually and generally coincided with either the peak or the rise and fall of the temperature cycles.  Vertical distribution of Cyclopoids was relatively uniform, whereas Daphnia were more abundant near the surface and Bosmina were most numerous at depth.  Stomach contents of juvenile chinook salmon revealed that zooplankton, especially Daphnia, were the major items of the diet from July through October; the most important season tor fish growth.  Insects were the prime constituents of the diet the remainder of the year.