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8 <br />Razorback suckers are in imminent danger of extirpation in the wild. The <br />specific causes of this species' continued decline are largely unknown at this <br />time. As Bestgen (1990) pointed out: <br />"Reasons for decline of most native fishes in the Colorado River <br />Basin have been attributed to habitat loss due to construction of <br />mainstream dams and subsequent interruption or alteration of <br />natural flow and physio-chemical regimes, inundation of river <br />reaches by reservoirs, channelization, water quality degradation, <br />introduction of nonnative fish species and resulting competitive <br />interactions or predation, and other man-induced disturbances <br />(Miller 1961, Joseph et al. 1977, Behnke and Benson 1983, Carlson <br />and Muth 1989, Tyus and Karp 1989). These factors are almost <br />certainly not mutually exclusive, therefore it is often difficult <br />to determine exact cause and effect relationships." <br />The virtual absence of any recruitment suggests a combination of biological, <br />physical, and/or chemical factors that may be affecting the survival and <br />recruitment of early life stages of razorback suckers. Within the Upper <br />Basin, recovery efforts endorsed by the Recovery Implementation Program <br />include the capture and removal of razorback suckers from all known locations <br />for genetic analyses and development of discrete brood stocks if necessary. <br />These measures have been undertaken to develop refugia populations of the <br />razorback sucker from the same genetic parentage as their wild counterparts <br />such that, if these fish are genetically unique by subbasin or individual <br />population, then separate stocks will be available for future augmentation. <br />Such augmentation may be a necessary step to prevent the extinction of <br />razorback suckers in the Upper Basin. <br />Critical Habitat <br />Critical habitat has been proposed within the 100-year floodplain of the <br />razorback sucker'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 mouth of Cross Mountain Canyon in T. 6 N., R. 98 W., section 23 <br />(6th Principal Meridian) to the confluence with the Green River in <br />T. 7 N., R. 103 W., section 28 (6th Principal Meridian). <br />Utah, Uintah County; and Colorado, Moffat County. The Green River and <br />its 100-year floodplain from the confluence with the Yampa River in <br />T. 7 N., R. 103 W., section 28 (6th Principal Meridian) to Sand Wash at <br />river mile 96 in T. 1] S., R. 18 E., section 20 (6th Principal <br />Meridian): <br />Green River and-its 100-year floodpla <br />at T: 11 S., R. 18 E., section 20 (6t <br />confluence with the Colorado River in <br />(6th Principal Meridian).. <br />yne, and San Juan Counties. The <br />n:from Send•Wash at river mile 96 <br />Principal Meridian) to the <br />T. 30 S., R. 19 E., section 7 <br />