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RAZORBACK SUCKER <br />Species Description <br />Like all suckers (family Catastomidae, meaning "down mouth"), the razorback sucker <br />has a ventral mouth with thick lips covered with papillae and no scales on its head. In <br />general, suckers are bottom browsers, sucking up or scraping off small invertebrates, <br />algae, and organic matter with their fleshy, protrusible lips (Moyle 1976). The razorback <br />sucker is the only sucker with an abrupt sharp-edged dorsal keel behind its head. The <br />keel becomes more massive with age. The head and keel are dark, the back is <br />olive-colored, the sides are brownish or reddish, and the abdomen is yellowish white <br />(Sublette et al. 1990). Adults often exceed 3 kilograms (6 pounds) in weight and <br />600 millimeters (2 feet) in length. Like Colorado pikeminnow, razorback suckers are <br />long-lived, living 40-plus years. <br />Status and Distribution <br />On March 14, 1989, the Service was petitioned to conduct a status review of the <br />razorback sucker. Subsequently, the razorback sucker was designated as endangered <br />under a final rule published on October 23, 1991 (56 FR 13374). The final rule stated <br />"Little evidence of natural recruitment has been found in the past 30 years, and numbers <br />of adult fish captured in the last 10 years demonstrate a downward trend relative to <br />historic abundance. Significant changes have occurred in razorback sucker habitat <br />through diversion and depletion of water, introduction of nonnative fishes, and <br />construction and operation of dams" (56 FR 13374). Recruitment of razorback suckers to <br />the population continues to be a problem. <br />Historically, razorback suckers were found in the mainstem Colorado River and major <br />tributaries in Arizona, California, Colorado, Nevada, New Mexico, Utah, Wyoming, and <br />in Mexico (Ellis 1914; Minckley 1983). Bestgen (1990) reported that this species was <br />once so numerous that it was commonly used as food by early settlers and, further, that <br />commercially marketable quantities were caught in Arizona as recently as 1949. In the <br />Upper Basin, razorback suckers were reported in the Green River to be very abundant <br />near Green River, Utah, in the late 1800s (Jordan 1891). An account in Osmundson and <br />Kaeding (1989) reported that residents living along the Colorado River near Clifton, <br />Colorado, observed several thousand razorback suckers during spring runoff in the 1930s <br />and early 1940s. In the San Juan River drainage, Platania and Young (1989) relayed <br />historical accounts of razorback suckers ascending the Animas River to Durango, <br />Colorado, around the turn of the century. <br />A marked decline in populations of razorback suckers can be attributed to construction of <br />dams and reservoirs, introduction of nonnative fishes, and removal of large quantities of <br />water from the Colorado River system. Dams on the mainstem Colorado River and its <br />major tributaries have segmented the river system, blocked migration routes, and changed <br />river habitat into lake habitat. Dams also have drastically altered flows, temperatures, <br />and channel geomorphology. These changes have modified habitats in many areas so <br />that they are no longer suitable for breeding, feeding, or sheltering. Major chan ges in <br />species composition have occurred due to the introduction of numerous nonnative fishes, <br />16