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point-sources for mercury resulting from the project. As with the Colorado pikeminnow,we <br /> believe nonnative species are the primary limiting factor for bonytail numbers, successful <br /> recruitment, and their distribution within the action area. While the data presented above <br /> supports the reasonable assumption that some bonytail individuals are likely being adversely <br /> affected by mercury in the system, we do not see evidence indicating that the negative effects <br /> from mercury rise to the level of reducing population numbers, are limiting reproduction, or are <br /> constraining bonytail distribution. <br /> 4.2.2 Selenium <br /> Selenium is required in the diet of fish at very low concentrations (0.1 µg/g) (Sharma and Singh <br /> 1984), but at higher concentrations it becomes toxic. The safe level of selenium concentration in <br /> water for protection of fish and wildlife is considered to be less than 2 ug/L, and chronically <br /> toxic levels are considered by some to be greater than 2.7 ug/L (Lemly 1993; Maier and Knight <br /> 1994). In Colorado,the chronic aquatic life standard for total selenium in water is 5 µg/L (=4.6 <br /> ug/L dissolved) (CDPHE 2012a). However, dietary selenium is the primary source for selenium <br /> in fish (Lemly 1993); selenium in water is less important than dietary exposure when <br /> determining the potential for chronic effects to a species (USEPA 1998). <br /> Excess selenium in fish has been shown to have a wide range of adverse effects including <br /> mortality,reproductive impairment, effects on growth, and developmental and teratogenic effects <br /> including edema and finfold, craniofacial, and skeletal deformities (Lemly 2002). Excess dietary <br /> selenium also causes elevated selenium concentrations to be deposited into developing eggs, <br /> particularly the yolk(Lemly 2002, Janz et al. 2010, Buhl and Hamilton 2000). If concentrations <br /> in the egg are sufficiently high, developing proteins and enzymes become dysfunctional or result <br /> in oxidative stress, conditions that may lead to embryo mortality, deformed embryos, or embryos <br /> that may be at higher risk for mortality. <br /> Of the four Colorado River fish species,we expect that excess selenium would <br /> disproportionately affect the razorback sucker somewhat more than the other three species <br /> (Hamilton et al. 2002; Osmundson et al. 2010). As with all sucker species,the razorback sucker <br /> is a bottom feeder and more likely to ingest selenium that has adsorbed to river sediments. <br /> Simpson and Lusk(1999) and Osmundson and Lusk(2011)reported on the concentrations of <br /> selenium in muscle tissues collected from Colorado pikeminnow and razorback suckers from the <br /> San Juan River. They found higher concentrations in razorback sucker than in Colorado <br /> pikeminnow; however,the average difference was only modest(3.5 mg/kg in razorback suckers <br /> vs. 3.0 mg/kg in Colorado pikeminnow, dry weight). <br /> As stated in the Baseline section, the Yampa River has not exceeded the aquatic chronic toxicity <br /> standard for selenium. Water selenium concentrations in the White River have always registered <br /> below the chronic standard. Neither river is listed as impaired in the 303(d) EPA Clean Water <br /> Act list. <br /> 4.3.2.1 Colorado pikeminnow <br /> Despite low selenium concentrations in the Yampa and White Rivers, selenium was detected at <br /> high levels in Colorado pikeminnow tissue in the 1960s in the Yampa River. In the White River, <br /> 54 <br />