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<br />~. <br /> <br />. <br /> <br />. <br /> <br />.. <br /> <br />.. <br /> <br />" <br /> <br />~. <br />i :I <br /> <br />11 <br /> <br />almost entirely of other fishes (Vanicek and Kramer 1969). The Colorado <br />squawfish is the largest cyprinid fish (minnow family) native to North America <br />and, during predevelopment times, may have grown as large as 6 feet in length, <br />with weights near 100 pounds (Behnke and Benson 1983). These large fish are <br />thought to have been 25 to 50 years of age. <br /> <br />Based on early fish collection records, archaeological finds, and other <br />observations, the Colorado squawfish was once found throughout warmwater <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. Colorado squawfish were <br />apparently never found in colder, headwater areas. Seethaler (1978) indicates <br />that Colorado squawfish were abundant in suitable habitat throughout the <br />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 />Rifle, Colorado (Beckman 1952). <br /> <br />A marked decline in Colorado squawfish populations can be closely correlated <br />with the construction of dams and reservoirs, the introduction of nonnative <br />fishes, and the removal of water from the Colorado River system. Behnke and <br />Benson (1983) summarized the decline of the natural ecosystem. They pointed <br />out that dams, impoundments, and water-use practices are probably major <br />reasons for drastically modified natural river flows and channel <br />characteristics in the Colorado River basin. Dams on the mainstem have <br />essentially segmented the river system, blocking spawning migrations and <br />drastically changing river characteristics, especially flows and temperatures. <br />Channeliration, dams, and water use patterns in the mainstem and tributary <br />streams have reduced or nearly eliminated embayments and backwaters in some <br />reaches of river. In addition, major changes in species composition have <br />occurred due to the introduction of nonnative fishes and have thrived as a <br />result of changes in the natural riverine system (i.e., flow and temperature <br />regimes). The decline of endemic Colorado River fishes appears to be at least <br />partially related to competition or other behavioral interactions with <br />nonnative species, which have perhaps been exacerbated by alterations in the <br />natural fluvial environment. <br /> <br />The Colorado squawfish currently occupies about 880 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 156 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 <br />33 miles of the Gunnison River, a tributary to the mainstem Colorado River <br />(Tyus et al. 1982). <br /> <br />BioloQY <br /> <br />The life-history phases that appear to be most critical for the Colorado <br />squawfish include spawning, egg fertilization, and development of larvae <br />through the first year of life. These phases of Colorado squawfish <br />development are tied closely to specific habitat requirements. Natural <br />