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species feeds primarily on algae, aquatic insects, and other available aquatic macroinvertebrates <br /> using their ventral mouths and fleshy lips (Sigler and Sigler 1996). Adults can be identified by <br /> olive to dark brown coloration above, with pink to reddish brown sides and a bony, sharp-edged <br /> dorsal keel immediately posterior to the head, which is not present in the young. The species can <br /> reach lengths of 3 ft and weights of 16 pounds (7.3 kg), but the maximum weight of recently <br /> captured fish is 11 to 13 pounds (5 to 6 kg) (Sigler and Sigler 1996; Service 2002b). <br /> Taxonomically,the species is unique,belonging to the monotypic genus Xyrauchen, meaning <br /> that razorback sucker is the only species in the genus (Service 2002b). Like Colorado <br /> pikeminnow,razorback suckers may live to be greater than 40 years. <br /> Historically, the razorback sucker occupied the mainstem Colorado River and many of its <br /> tributaries from northern Mexico through Arizona and Utah into Wyoming, Colorado, and New <br /> Mexico (Service 2002b). In the late 19th and early 20th centuries, it was abundant in the Lower <br /> Colorado River Basin and common in parts of the Upper Colorado River Basin, with numbers <br /> apparently declining with distance upstream (Service 2002b). Bestgen (1990)reported that this <br /> species was once so numerous that it was commonly used as food by early settlers and that a <br /> commercially marketable quantity was caught in Arizona as recently as 1949. Distribution and <br /> abundance of razorback sucker declined throughout the 20th century across its historic range, <br /> and the species now exists naturally only in a few small,unconnected populations or as dispersed <br /> individuals. Specifically,razorback sucker are currently found in small numbers in the Green <br /> River,upper Colorado River, and San Juan River sub-basins; the lower Colorado River between <br /> Lake Havasu and Davis Dam; Lakes Mead and Mohave; in small tributaries of the Gila River <br /> sub-basin (Verde River, Salt River, and Fossil Creek); and in local areas under intensive <br /> management such as Cibola High Levee Pond, Achii Hanyo Native Fish Facility, and Parker <br /> Strip (Service 2002b). <br /> The razorback sucker is listed as endangered under the Endangered Species Act of 1973, as <br /> amended (ESA; 16 U.S.C. 1531 et. seq.),under a final rule published on October 23, 1991 <br /> (56 FR 54957). The Service finalized the latest recovery plan for the species in 2002 (2002b), <br /> but is currently drafting an updated revision. <br /> Fifteen reaches of the Colorado River system were designated as critical habitat for the razorback <br /> sucker totaling 2,776 km (1,724 mi) as measured along the center line of the river within the <br /> subject reaches. Designated critical habitat makes up about 49 percent of the species' original <br /> range and occurs in both the Upper and Lower Colorado River Basins. In the Upper Basin, <br /> critical habitat is designated for portions of the Green,Yampa, Duchesne, Colorado, White, <br /> Gunnison, and San Juan Rivers. Portions of the Colorado, Gila, Salt, and Verde Rivers are <br /> designated in the Lower Basin. <br /> Separate, objective recovery criteria were developed for each of two recovery units (the Upper <br /> Colorado and Lower Colorado River Basins as delineated at Glen Canyon Dam)to address <br /> unique threats and site specific management actions necessary to minimize or remove those <br /> threats. This BOs focus is on the Upper Colorado River Basin recovery unit and will therefore <br /> describe the status of the razorback sucker in that unit. <br /> 16 <br />