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Since 2007, we have partnered with the Shoshone-Paiute Tribes of the Duck Valley Indian Reservation to evaluate mercury concentrations in fish tissue in Duck Valley reservoirs.
In 2008, the Tribes asked the USGS to complete a more comprehensive watershed study to evaluate mercury concentrations in catchable rainbow trout and to assess the condition of the fish community in relation to water temperatures along the East Fork Owyhee River.
USGS biologists collected fish tissue and aquatic macroinvertebrate samples, and measured water temperature at four sites along the East Fork Owyhee River.
We used standard boat electrofishing to collect 15 catchable (> 12 inch) rainbow trout and/or small-mouth bass from each river site. One-inch, skinless fish tissue samples were taken from each fish. The samples were analyzed for total mercury concentrations at the USGS Mercury Laboratory in Middleton, WI. Additional samples were analyzed for selenium at the USGS Research Laboratory in Atlanta, GA.
While collecting sport fish for tissue analysis, we identified, counted, measured, and classified native and non-native fish. We also measured water temperature. Together, these data were used to evaluate the health of the aquatic community.
We collected caddisflies from riffle habitat and analyzed them for trace metals such as arsenic, cadmium, copper, mercury, lead, selenium, and zinc.
The concentrations of mercury in the fish collected during this study were higher than what would normally be expected in western lakes and reservoirs. Two fish had mercury concentrations above the U.S. Environmental Protection Agency criterion for human consumption of 0.3 mg/kg wet weight. In general, bigger fish had higher mercury concentrations.
To further define "baseline" or "background" mercury concentrations in fish tissue in the area, it'd be useful to collect additional information from numerous water bodies in Idaho and Nevada.
Upstream diversion and channel straightening may be contributing to higher summer water temperatures. Water temperature at the two most downstream of the four sites in this study regularly exceeded the 20-degree (C°) criteria to support cold-water aquatic life. Higher water temperatures at the two downstream sites are probably the primary reason for the lower numbers of rainbow trout and sculpin.
Results from this study were presented to the Tribes’ water resource managers.
The water temperature and fish tissue data are available from the USGS National Water Information System—see the samples from 2008.
Fish community data are available in the USGS Fish On-line Database—use the map or menus to search "Owyhee River" and see the samples from 2008.
To request macroinvertebrate and other data, please contact us.
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