Distribution of Debris and Downstream-Migrating Salmon in the Snake River above Brownlee Reservoir

Abstract The distribution of chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon migrating downstream and the weight and vertical distribution of various types of debris were studied above Brownlee Reservoir in the Snake River during the spring and early summer of 1964. Electrified fyke nets were used in the fish sampling. Salmon and debris were present simultaneously and were distributed throughout the cross section of the river. Most of the salmon were in the upper 2.4 m of water, although appreciable numbers migrated at all depths; more migrants were in each of the two outer thirds of the river than in the middle third. Large quantities of debris, which represented a wide range of materials from algae to parts of buildings, were distributed throughout the river. To effectively collect most of the salmon migrating downstream, the entire water mass will need to be strained by some method which has the capacity to cope with large quantities of debris.