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4 <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, excluding the San Juan River Basin (58 F.R. 6578). <br />Colorado, Moffat County. The Yampa River and its 100-year floodplain <br />from the State Highway 394 bridge (river mile 137.7) in T. 6 N., <br />R. 91 W., section 1 (6th Principal Meridian) to the confluence with the <br />Green River in T. 7 N., R. 103 W., section 28 (6th Principal Meridian). <br />t,oioraao, mortar bounty. ine tireen rclver ana Its -uu-year riooapialn <br />from the confluence with the Yampa River in T. 1 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, Rio Blanco County: and Utah, Uintah County. The White River <br />and its 100-year floodplain from Rio Blanco Lake Dam (river mile 150) in <br />T. 1 N., R. 96 W., section 6 (6th Principal Meridian) to the confluence <br />with the Green River in T. 9 S., R. 20 E., section 4 (Salt Lake <br />Meridian). <br />Colorado, Delte and Mesa Counties.: The Gunnison River an.d.its 100=year <br />flobdp~lain from the confluence with the Uncompahgre River in T: '15 S.; <br />R. 96 W., section 11 (6th Principal Meridian) to the confluence with the <br />Colorado River in T. I S., R. I W., section 22 (Ute Meridian). <br />