South Platte River Basin Assessment Report

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cold water fish, and dissolved oxygen is nearly always at or above ' saturation levels (U.S. Department of the Interior, 1974). ' Cold water habitat is characterized by a less diverse fauna and generally less biomass production than in warmer, nutrient -rich waters ' (Li, 1968; U.S. Department of the Interior, 1974). Species of invertebrates are the common food source for most cold water fish. ' Common stream invertebrates in the upper South Platte River basin include mayflies, stoneflies, blackflies, and midges (U.S. Department of the Interior, 1974). Introduced and native trout species, ' including brook, brown, rainbow, cutthroat and lake trout, represent the primary fish species in the cold water fisheries. Two native fish species that are found in Colorado cold water fisheries, the johnny darter and the greenback cutthroat trout, have been listed as threatened and endangered, respectively (Colorado Division of Wildlife, 1978). The johnny darter is sometimes referred to as a warm water species; however, it does exist in marginal cold water habitat. Common species, such as rainbow, cutthroat, brown trout, and brook trout, are introduced species which are the dominate cold water species. The existence of the greenback cutthroat trout has been threatened because of its competition with introduced fish species. Attempts to reestablish the greenback cutthroat trout have not been successful (Larimer -Weld Regional Council of Governments and Toups Corporation, 1978). Warm Water Fisheries - Being a warm water fishery, the lower South Platte River and its associated plains tributaries and reservoirs are more productive than cold water fisheries in terms of biomass and species diversity (Li, 1968). However, the major fish species are less desirable, that is, "rough" fish such as carp and suckers (Larimer -Weld Regional Council of Governments and Toups Corporation, 1978). -13-