Cutthroat Trout Avoidance of Metals and Conditions Characteristic of a Mining Waste Site: Coeur d'Alene River, Idaho

Abstract

The South Fork basin of the Coeur dˈAlene River, Idaho, has been an area of heavy mining activity since the 1880s. The mining operations have resulted in elevated concentrations of metals in surface water, most notably cadmium, lead, zinc, and, to a lesser extent, copper. The metals affected surface water quality downstream in the Coeur dˈAlene basin and are suspected to be one of the primary reasons for the reduction in populations of native westslope cutthroat trout Oncorhynchus clarki lewisi. The avoidance response of a surrogate species, Snake River cutthroat trout O. clarki (unnamed subspecies), was evaluated against conditions simulating those in the Coeur dˈAlene River basin. Cutthroat trout avoided a metals mixture of these concentrations: Cd (0.30 μg/L), Cu (6.0 μg/L), Pb (0.6 μg/L), and Zn (28 μg/L). The avoidance response to either Cu or Zn alone was similar to the avoidance response to the mixture, suggesting that avoidance to the mixture was due to these metals. After acclimation to Zn at 55 μg/L for 90 d, cutthroat trout detected and preferred a lower Zn concentration of 28 μg/L. The lowest Zn concentrations avoided (28 μg/L) were 1/6 to 1/78 the Zn concentrations measured in the South Fork and lower Coeur dˈAlene River basins. Avoidance of metals-contaminated habitats by cutthroat trout may be, in part, responsible for reduced fish populations.