CUTTHROAT TROUT AVOIDANCE OF METALS AND CONDITIONS CHARACTERISTIC OF A MINING WASTE SITE - COEUR-DALENE RIVER, IDAHO

The South Fork basin of the Coeur d'Alene River, Idaho, has been an ar ea of heavy mining activity since the 1880s. The mining operations hav e resulted in elevated concentrations of metals in surface water, most notably cadmium, lead, zinc, and, to a lesser extent, copper. The met als affected surface water quality downstream in the Coeur d'Alene bas in and are suspected to be one of the primary reasons for the reductio n in populations of native westslope cutthroat trout Oncorhynchus clar ki 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 d'Alene River basin. Cutthroa t trout avoided a metals mixture of these concentrations: Cd (0.30 mu g/L), Cu (6.0 mu g/L), Pb (0.6 mu g/L), and Zn (28 mu g/L). The avoida nce response to either Cu or Zn alone was similar to the avoidance res ponse to the mixture, suggesting that avoidance to the mixture was due to these metals. After acclimation to Zn at 55 mu g/L for 90 d, cutth roat trout detected and preferred a lower Zn concentration of 28 mu g/ L. The lowest Zn concentrations avoided (28 mu g/L) were 1/6 to 1/78 t he Zn concentrations measured in the South Fork and lower Coeur d'Alen e River basins. Avoidance of metals-contaminated habitats by cutthroat trout may be, in part, responsible for reduced fish populations.