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category which indicates "that no toxic threat is identified but concentrations of selenium are <br /> slightly elevated in one or more ecosystem components (water, sediment, invertebrates, fish, <br /> birds) compared to uncontaminated reference sites; continued comprehensive environmental <br /> monitoring is recommended." Thus, tissue selenium concentrations in Colorado pikeminnow <br /> from the Yampa River have varied over time, with earlier values indicating a high hazard and <br /> more recent values indicating a minimal hazard. <br /> 3.4 Climate Change In The Action Area <br /> We discuss climate change on a global and regional level in the Status of the Species section <br /> above (2.6). That discussion includes the action area. In this section we provide further insights <br /> into the potential effects of climate change within the action area. <br /> Native fish in the Yampa River could potentially move upstream in response to periods of <br /> warming and drying associated with climate change because there is no dam blocking up-river <br /> migration. In the White River,however,the Taylor Draw Dam precludes migration to <br /> potentially more favorable upstream areas as a behavioral adaptation to changing climatic <br /> conditions. The Yampa and White Rivers are at the upper end of the distribution of the <br /> endangered fishes within the Colorado River watershed, however. As far as water temperatures <br /> are concerned, these fish inhabit warmer waters downstream and are presumably not currently <br /> near the upper limit of their temperature tolerances within any given season unless low flows and <br /> dry conditions become a problem,which can greatly affect water temperature. <br /> If the modeled predictions of more frequent,more severe, and possibly longer-lasting droughts, <br /> along with generally warmer temperatures and less snowfall occur, it will likely become <br /> increasingly challenging to meet the established flow recommendations for the protection of <br /> listed and native fish in the Yampa and White Rivers (Service 2005, 2013). Reduced flow levels <br /> may also exacerbate contaminant issues, as less dilution of contaminants in the river would <br /> occur. <br /> Climate change could also affect nonnative fish in the action area, which we believe to be the <br /> greatest threat to the endangered fish in the action area. As stated in Martinez et al. (2014), the <br /> challenges in restoring and conserving native aquatic species will likely become more difficult <br /> due to the interaction of invasive species and climate change. The abundance of nonnative <br /> species can increase rapidly under favorable conditions such as low flow prolonged by drought. <br /> Reductions in water stores and stream flows due to climate change may intensify demand for <br /> remaining water supplies and may hasten proposed water development, including in the Yampa <br /> River. <br /> Long-term climate and water development forecasts suggest flow scenarios for the Yampa River <br /> that will functionally mimic drought conditions,including reduced stream discharge, smaller <br /> stream size, and an increase in summertime water temperatures (Roehm 2004; Johnson et al. <br /> 2008). Several invasive species, including green sunfish Lepomis cyanellus and largemouth bass <br /> Micropterus salmoides,have higher thermal tolerances than many of the fish species native to <br /> the Colorado River Basin. The projected increase in channel catfish growth rate (McCauley and <br /> Beitinger 1992) could increase piscivory by larger catfish in the Colorado River Basin. <br /> 41 <br />