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<br />o. <br /> <br />{"":") <br /> <br />. (,,, <br /> <br />;,"\ <br /> <br />5 <br /> <br />en <br />hJ <br /> <br />The razorback sucker was listed as endangered on October 23, 1991. Causes for the <br />decline of the sucker have been identified as fragmentation of its habitat by the <br />construction of dams, the manipulation of flows with attendant alterations of temperature <br />and water quality, and the introduction of non-native fishes. Once abundant throughout <br />the mainstem of the Colorado River and its major tributaries, the species now occupies <br />only an estimated 25 percent of its historic range, and where it does occur, its numbers <br />are extremely low. <br /> <br />Critical habitat has been designated for the razorback sucker in the San Juan River and <br />its 1OQ-year floodplain from the Hogback Diversion Dam in T.29N., R.16W., section 9 <br />(New Mexico Meridian) to the full pool elevation at the mouth of Neskahai Canyon on the <br />San Juan arm of Lake Powell;n T.41S., R.11E., section 26 (Salt Lake Meridian). <br /> <br />Information on the historic distribution and abundance of the razorback sucker in the San <br />Juan basin is sparse. The number of fishery surveys that have been conducted in the <br />San Juan River is relatively small compared to the rest of the Colorado River Basin. <br />Anecdotal reports of the species from the Animas River near Durango (1891), and the <br />San Juan River near Farmington (1960) may or may not have been razorback sucker <br />(Platania 1990). Pre-impoundment piscicide'applications in the Navajo Dam area in 1962 <br />killed fish downriver to Farmington, New Mexico; however, no razorback sucker were <br />documented among the fish killed (Olson 1962). The first verifiable record of razorback <br />sucker from the San Juan River basin was in 1976 when two adults were seined from a <br />pond near Bluff, Utah, at approximately river mile 81 (VTN Consolidated Inc., and <br />Museum of Northern Arizona 1978, Platania 1990, Minckley et al1991). According to <br />local residents, a second pond adjacent to the one where these two fish were caught was <br />drained just weeks before, leaving approximately 100-250 juvenile razorback sucker <br />stranded, resulting in the mortality of all fish at the site. These two ponds were linked to <br />the river via a canal that allowed fish movement to and from the river (VTN Consolidated <br />Inc., and Museum of Northern Arizona 1978. Platania 1990, Minckley et al 1991). <br />Between 1987 and 1989 sixteen adult razorback sucker were collected from the San Juan <br />River arm of Lake Powell, near Piute Farms Marina (Platania 1990). In 1988 one <br />razorback sucker was captured and released in the main channel of the San Juan River <br />near Bluff, Utah, close to the 1976 capture site. <br /> <br />No wild razorback sucker have been collected from the San Juan River in Colorado or <br />New Mexico. Neither have spawning or recruitment been documented in the San Juan <br />River. However, the presence of a few large adult fish near Bluff, Utah, suggests that <br />there is a remnant population of old razorback sucker remaining in the river. <br /> <br />As has been evidenced by the small number of wild fish captured in the San Juan River, <br />the razorback sucker is the least abundant of the three target species (razorback sucker, <br />Colorado squawfish, and roundtail chub, Gila robusta) in this river system (Ryden and <br />Pfeifer 1993, Platania 1990). For this reason, it was considered necessary to begin <br />experimental stocking for the purpose of obtaining basic information about this species <br />