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Ira W. Hatch, District Ranger 4 <br />A marked decline in Colorado squawfish populations can be closely correlated <br />with the construction of dams and reservoirs during the 1960's, introduction <br />of nonnative fishes, and removal of water from the Colorado River system. <br />Behnke and Benson (1983) summarized the decline of the natural ecosystem. <br />They pointed out that dams, impoundments, and water use practices are probably <br />the major reasons for drastically modified natural river flows and channel <br />characteristics in the Colorado River Basin. Dams on the main stem have <br />essentially segmented the river system, blocking Colorado squawfish spawning <br />migrations and drastically changing river characteristics, especially flows <br />and temperatures. In addition, major changes in species composition have <br />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 Basin above Glen Canyon Dam. It inhabits about <br />350 miles of the main stem Green River from its mouth to the mouth of the <br />Yampa River. Its range also extends 160 miles up the Yampa River and <br />104 miles up the White River, the two major tributaries of the Green River. <br />In the main stem 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 main stem Colorado River <br />(Tyus et al. 1982). <br />Critical Habitat <br />Critical habitat has been proposed within the 100 -year floodplain of the <br />Colorado squawfish's historical range in the following sections of the Upper <br />Basin, which are pertinent to this project (58 F.R. 6578): <br />Utah, Uintah, Carbon, Grand, Emery, Wayne, and San Juan Counties; and <br />Colorado, Moffat County. The Green River and its 100 -year floodplain <br />from the confluence with the Yampa River in T. 7 N., R. 103 W., <br />section 28 (6th Principal Meridian) to the confluence with the Colorado <br />River in T. 30 S., R. 19 E., section 7 (Salt Lake Meridian). <br />Colorado, Mesa and Garfield Counties: and Utah, Grand, San Juan, Wayne, <br />and Garfield Counties. The Colorado River and its 100 -year floodplain <br />from the Colorado River Bridge at exit 90 north off Interstate 70 (river <br />mile 238) in T. 6 S., R. 93 W., section 16 (6th Principal Meridian) to <br />North Wash, including the Dirty Devil arm of Lake Powell up to the full <br />pool elevation, in T. 33 S., R. 14 E., section 29 (Salt Lake Meridian). <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 />