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• Based on early fish collection records, archaeological finds and other <br />observations, the Colorado squawfish was once found throughout warm water <br />reaches of the entire Colorado River Basin, including reaches of the upper <br />Colorado River and its major tributaries, the Green River and its major <br />tributaries, and the Gila River system in Arizona (Seethaler 1978). Colorado <br />squawfish were apparently never found in colder, headwater areas. Seethaler <br />(]978) indicates that the species was abundant in suitable habitat throughout <br />the entire Colorado River basin prior to the 1850's. Historically, Colorado <br />squawfish have been collected in the upper Colorado River as far upstream as <br />Parachute Creek, Colorado (Kidd 1977). <br /> <br />CJ <br />A marked decline in Colorado squawfish populations can be closely correlated <br />with the construction of dams and reservoirs during the 1960's, the <br />introduction of nonnative fishes, and the removal of water from the Colorado <br />River system. Behnke and Benson (1983) summarized the decline of the natural <br />ecosystem. They pointed out that dams, impoundments, and water use practices <br />are probably the major reasons for drastically modified natural river flows <br />and channel characteristics in the Colorado River Basin. Dams on the mainstem <br />have essentially segmented the river system, blocking Colorado squawfish <br />spawning migrations and drastically changing river characteristics, especially <br />flows and temperatures. In addition, major changes in species composition <br />have occurred due to the introduction of nonnative fishes, many of which have <br />thrived as a result of changes in the natural riverine system (i.e., flow and <br />temperature regimes). The decline of endemic Colorado River fishes seems to <br />be at least partially related to competition or other behavioral interactions <br />with nonnative species, which have perhaps been exacerbated by alterations in <br />the natural fluvial environment. <br />The Colorado squawfish currently occupies about 1,030 river miles in the <br />Colorado River system (25 percent of its original range) and is presently <br />found only in the upper Colorado River Basin above Glen Canyon Dam. It <br />inhabits about 350 miles of the mainstem Green River from its mouth to the <br />mouth of the Yampa River. Its range also extends 140 miles~up the Yampa River <br />and 104 miles up the White River, the two major tributaries of the Green <br />River. In the mainstem Colorado River, it is currently found from Lake Powell <br />extending about 201 miles upstream to Palisade, Colorado, and in the lower 33 <br />miles of the Gunnison River, a tributary to the mainstem Colorado River (Tyus <br />et al. 1982). Recent investigation found adult Colorado squawfish inhabit the <br />San Juan River as far upstream as 163.3 miles above Lake Powell. <br />The life stages that appear to be most critical are from egg fertilization <br />through its first year of life. It has been demonstrated that these phases of <br />Colorado squawfish development are also closely tied to some specific habitat <br />requirements. It is imperative that proper flows and temperatures are <br />provided during these essential life stages. The Conservation Measures <br />outlined below will help further investigate and meet the habitat requirements <br />of the Colorado squawfish, thus offsetting project-related impacts and the <br />likelihood of jeopardy for the species. <br />Humpback chub <br />Humpback chub generally do not make migrational movements in the upper <br />Colorado River and tend to reside throughout the year within a limited reach <br />of river. Humpback chub are found inhabiting narrow, deep canyon areas, and <br />