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15 <br />sheltering. Major changes in species composition have occurred due to <br />the introduction of numerous nonnative fishes, many of which have <br />thrived due to man-induced changes to the natural riverine system. <br />Critical habitat was designated in 1994 within the 100-year floodplain <br />of the razorback sucker's historical range in the following area of <br />the Upper Colorado River (59 F.R. 13374). The primary constituent <br />elements are the same as critical habitat for Colorado pikeminnow <br />described above. <br />olo ado Meaa and .arfietd ovn ; a. The Colorado River and its <br />100-year floodplain from Colorado River Bridge at exit 90 north <br />off Interstate 70 in T. 6 S., R. 93 W., section 16 (6th Principal <br />Meridian) to Westwater Canyon in T. 20 S., R. 25 E., section 12 <br />(Salt Lake Meridian) including the Gunnison River and its 100-year <br />floodplain from the Redlands Diversion Dam in T. 1 S., R. 1 W., <br />section 27 (Ute Meridian) to the confluence with the Colorado <br />River in T. 1 S., R. 1 W., section 22 (Ute Meridian). <br />o~orado- n ~ a and M ga ro,n ; a, The Gunnison River and its <br />100-year floodplain from the confluence with the Uncompahgre River <br />in T. 15 S., R. 96 W., section 11 (6th Principal Meridian) to <br />Redlands Diversion Dam in T. 1 S., R. 1 W., section 27 (Ute <br />Meridian) . <br />iitah. Grand. San Tnan. Wayne. and Ga f;.ld o m i.s. The Colorado <br />River and its 100-year floodplain from Westwater Canyon in <br />T. 20 S., R. 25 E., section 12 (Salt Lake Meridian) to full pool <br />elevation, upstream of North Wash, and including the Dirty Devil <br />arm of Lake Powell in T. 33 S., R. 14 E., section 29 (Salt Lake <br />Meridian). <br />The current distribution and abundance of the razorback sucker have <br />been significantly reduced throughout the Colorado River system, due <br />to lack of recruitment to the adult population (McAda 1987; McAda and <br />Wydoski 1980; Holden and Stalnaker 1975; Minckley 1983; Marsh and <br />Minckley 1989; Tyus 1987). The only substantial population exists in <br />Lake Mohave with an estimated population of 25,000 adult razorback <br />suckers in 1995 (Chuck Minckley pers. com.) down from an earlier <br />estimate of 60,000 adult razorback suckers (Minckley et al. 1991). <br />They do not appear to be successfully recruiting. While limited <br />numbers of razorback suckers persist in other locations in the Lower <br />Colorado River, they are considered rare or incidental and may be <br />continuing to decline. <br />In the Upper Basin, above Glen Canyon Dam, razorback suckers are found <br />in limited numbers in both lentic and lotic environments. The largest <br />. population of razorback suckers in the Upper Basin is found in the <br />