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and 393 millimeters total length) razorback suckers were collected in the lower Green <br />River near Hell Roaring Canyon (Gutermuth et al. 1994). Juvenile razorback suckers <br />have been collected in recent years from Old Charley Wash, a wetland adjacent to the <br />Green River (Modde 1996). Between 1992 and 1995 larval razorback suckers were <br />collected in the middle and lower Green River and within the Colorado River inflow to <br />Lake Powell (Muth 1995). In 2002, eight larval razorback suckers were collected in the <br />Gunnison River (Osmundson 2002b). No young razorback suckers have been collected <br />in recent times in the Colorado River. <br />Population Dynamics <br />The largest concentration of razorback suckers in the Upper Basin exists in low-gradient <br />flat-water reaches of the middle Green River between and including the lower few miles <br />of the Duchesne River and the Yampa River (Tyus 1987; Tyus and Karp 1990; Muth <br />1995; Modde and Wick 1997; Muth et al. 2000). This area includes the greatest expanse <br />of floodplain habitat in the Upper Colorado River Basin, between Pariette Draw at River <br />Mile (RM) 238 and the Escalante Ranch at RM 310 (Irving and Burdick 1995). <br />Lanigan and Tyus (1989) used a demographically closed model with capture-recapture <br />data collected from 1980 to 1988 and estimated that the middle Green River population <br />0 <br />consisted of about 1,000 adults (mean, 948; 95 percent confidence interval, 758-1,138). <br />Based on a demographically open model and capture-recapture data collected from 1980 <br />to 1992, Modde et al. (1996) estimated the number of adults in the middle Green River <br />population at about 500 fish (mean, 524; 95 percent confidence interval, 351-696). That <br />population had a relatively constant length frequency distribution among years (most <br />frequent modes were in the 505-51.5 millimeters total length interval) and an estimated <br />annual survival rate of 71 percent. Bestgen et al. (2002) estimated the current population <br />of wild razorback sucker in the middle Green River to be much lower than earlier <br />estimates -- about 100 -- based on data collected in 1998 and 1999. There are no current <br />population estimates of razorback sucker in the remainder of the upper Colorado River <br />basin due to low numbers captured in recent years. <br />From 1995 through 2004, 89,730 subadult razorback sucker were stocked into the Green <br />and Colorado subbasins. Monitoring and evaluation of stocked fish is ongoing. <br />Approximately 10,850 subadult and adult razorback sucker have been stocked in the Saxe <br />Juan River and reproduction has been documented through the collection of larvae every <br />year since 1998. Juvenile razorback sucker were found in the San Juan River in 2002 and <br />2003. <br />Critical Habitat <br />Critical habitat was designated in 1994 within the 100-year floodplain of the razorback <br />sucker's historical range in the following area of the upper Colorado River <br />(59 FR 13374). The PCEs are the same as critical habitat for Colorado pikeminnow <br />described previously, as is the status of the PCEs. We designated 15 reaches of the <br />Colorado River system as critical habitat for the razorback sucker. These reaches total <br />1,724 miles as measured along the center line of the river within the subject reaches. <br />19