2010-11-16_PERMIT FILE - C1996083A (27)

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20 • Rinne 199 ] ,and others). Data collected b}• Osmundson and Kaeding (1991) indicated that during 1o~v water years nonnative minnows capable of preying on or competing with larval endangered fishes greatly increased in numbers. Nonnative fishes compete with native fishes in several ways. The capacity of a particulaz area to support aquatic life is limited by physical habitat conditions. Increasing the number of species in an area usually results in a smaller population of most species. The size of each species population is controlled by the ability of each life stage to compete for space and food resources and to avoid predation. Some nonnative fishes' life stages appear to have a greater ability to compete for space and food and to avoid predation in the existing altered habitat than do some native fishes' life stages. Nonnative fishes are often stocked in and enter rivers from off-channel impoundments. The periodic introduction of these nonnative fishes into a river allows them to bypass limitations to reproduction, growth, or survival that they might encounter in the river. Consequently, populations of nonnative fishes in the river are enhanced. Endangered and other native species in the river experience greater competition and predation as a result. EFFECTS OF THE ACTION Water Ouantity The Project would cause an average annual new depletion of 155.6 acre-feet. Water Quality The Project's depletion would cause a proportionate decrease in dilution, which in tum would cause a proportionate increase in heavy metal, selenium, salts, PAHs, pesticides, and other contaminant concentrations in the Colorado River. An increase in contaminant concentrations in the river would likely result in an increase in the bioaccumulation ofthese contaminants in the food chain which could adversely affect the endangered fishes, particulazly the predatory Colorado pikeminnow~. Selenium is of particulaz concern due to its effects on fish reproduction and its tendency to concentrate in low velocity areas that are important habitats for Colorado pikeminnow and razorback suckers. Physical Habitat High spring flows are very important for creating and maintaining complex channel geomorphology and suitable spawning substrates, creating and providing access to off-channel habitats, and possibly stimulating Colorado pikeminnow spawning migrations. Adequate summer and winter flows are important for providing a sufficient quantity of preferred habitats for a duration and at a frequency necessary to support all life stages of viable populations of all