Movements of adult Chinook salmon during spawning migration in a metals-contaminated system, Coeur d'Alene River, Idaho

Spawning migration of adult male chinook salmon Oncorhynchus tshawytscha wa s monitored by radio telemetry to determine their response to the presence of metals contamination in the South Fork of the Coeur d'Alene River, Idaho . The North Fork of the Coeur d'Alene River is relatively free of metals co ntamination and was used as a control. In all, 45 chinook salmon were trans ported from their natal stream, Wolf Lodge Creek, tagged with radio transmi tters, and released in the Coeur d'Alene River 2 km downstream of the confl uence of the South Fork and the North Fork of the Coeur d'Alene River. Fixe d telemetry receivers were used to monitor the upstream movement of the tag ged chinook salmon through the confluence area for 3 weeks after release. D uring this period, general water quality and metals concentrations were mon itored in the study area. Of the 23 chinook salmon observed to move upstrea m from the release site and through the confluence area, the majority (16 f ish, 70%) moved up the North Fork, and only 7 fish (30%) moved up the South Fork, where greater metals concentrations were observed. Our results agree with laboratory findings and suggest that natural fish populations will vo id tributaries with high metals contamination.