Fishery Assessments on the Duck Valley Reservation, Idaho and Nevada, 2007-09

The U.S. Geological Survey and the Shoshone-Paiute Tribes of the Duck Valley Reservation cooperated to assess fishery resources in reservation reservoirs and East Fork Owyhee River. Decades of mining activity near the reservation prompted these assessments. This study evaluated mercury concentrations in fish tissue in reservoir and riverine habitats and evaluated the fish community along the East Fork Owyhee River. In 2007 and 2009, rainbow trout filet samples were collected for total mercury analysis from Mountain View, Billy Shaw, and Sheep Creek Reservoirs. In 2008, fish community and water temperature data were collected at four river sites. Rainbow trout filets from reservoirs (n=90) and four river sites (n=20) were analyzed for total mercury. Mercury concentrations were found above background concentrations (0.01-0.05 mg/g, wet weight in hatchery fish, n=15), but below concentrations that would warrant a fish consumption advisory. A Pacific Northwest Index of Biotic Integrity indicated impairment at the two lower river sites (scores of 34 and 57 out of 100), due primarily to the absence of coldwater native fish species (i.e., trout and sculpins). Water temperatures exceeding Idaho’s coldwater daily average criterion of 19⁰ C in the lower river may provide the best explanation for this impairment.