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. . . ,MAY-15-1998 15:50 BOR LULND 9706633212 P.ll/24 10 productive habitats; in recent years, flooded gravel pits may haye provided the only comparable habitat. The IS-mile reach has experienced major agricultural water depletions for many years. During late summer and early fall, this reach can be severely dewatered. Water depletions in the IS-mile reach have been identified as a limiting factor for Colorado squawffsh. Therefore, the Service has developed year-round flow recommendations for the IS-mile reach. These flow recommendations are based on adult Colorado squawflsh habitat preferences, stage v. habitat quantity and quality relationships, and discharge thresholds for sediment transport (Osmundson et al. 1995). Razorback Sucker The razorback sucker, an endemic specfes unique to the Colorado River Basin, was historically abundant and widely distributed within warmwater reaches throughout the Colorado River Basin. Historically, razorback suckers were found in the main stem Colorado River and major tributaries in Arizona, California, Colorado, Nevada, New Mexico, Utah, Wyoming, and in Mexico (Ellis 1914; Minckley 1983). Bestgen (1990) reported that this species was once so numerous that it was commonly used as food by early settlers and, further, that commercially marketable quantities were caught in Arizona as recently as 1949. In the Upper Basin, razorback suckers were reported in the Green River to be very abundant near Green River, Utah, in the late 1800's (Jordan 1891). An account in Osmundson and Kaeding (1989) reported that residents living along the Colorado River near Clifton, Colorado, observed several thousand razorback suckers during spring runoff In the 1930's and early 1940's. In the San Juan River drainage, Platania and Voung (1989) relayed historical accounts of razorback suckers ascending the Animas River to Durango, Colorado, around the turn of the century. A marked decline in populations of razorback suckers can be attributed to construction of dams and reseryoirs, introduction of nonnative fishes, and removal of large quantities of water from the Colorado River system. Dams on the main stem Colorado Rlyer and its major tributaries have segmented the river system and drastically altered flows, temperatures, and channel geomorphology. Major changes In species composition have occurred due to the introduction of numerous nonnative fishes, many of which have thrived due to man-induced changes to the natural riverine system. The current distribution and abundance of the razorback sucker have been significantly reduced throughout the Colorado River system (McAda 1987; McAda and Wydoski 1980; Holden and Stalnaker 1975; Minckley 1983; Marsh and Minckley 1989; Tyus 1987). The only substantial population of razorback suckers remaining, made up entirely of old adults (McCarthy and Minckley 1987), is found in lake Mohave; however, they do not appear to be successfully recruiting. While limited numbers of razorback suckers perSist in other locations in the lower Colorado River, they are considered rare or incidental and may be continuing to decl ine.