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<br />to olivaceous dorsally, with yellow or white sides and belly, Spawning adults intensify in color
<br />and develop pimple-like tubercles on the fins and body, that become largest and densest on the tail
<br />trunk and anal fin, Females are generally larger than males, and may grow to 915 nun TL and
<br />weigh 5-6 kg, Most adults are 410-690 nun TL and weigh 0,9-2,8 kg, Razorback suckers are
<br />reported to hybridize with flannelmouth and bluehead suckers (Hubbs and Miller 1953), and
<br />possibly with non-native white suckers (McAda and Wydoski 1980),
<br />
<br />Distribution
<br />
<br />Razorback suckers were once distributed from the Colorado River delta in the Gulf of Lower
<br />California, Mexico (Minckley 1973) to Rifle, Colorado (Beckman 1952), and throughout the
<br />major tributaries of the basin, including the Little Colorado, Virgin, Bill Wtlliams, Gila, San Juan,
<br />Green, White, Duchesne, Yampa, and Gunnison rivers, Spring spawning runs of razorback
<br />suckers into tributaries (Jordan 1891) indicate high historic populations, The species occurred in
<br />such great numbers that, in the early 1900's, its carcasses clogged irrigation systems, and it was
<br />sometimes applied to crops as fertilizer (Quartarone 1995), Fur fanners in the upper basin fed
<br />them to mink as a nutritious food,
<br />
<br />Razorback suckers began to decline in the lower basin with construction of Hoover Dam in 1935
<br />(Dill 1944, Wallis 1951), and decreased dramatically in distribution and numbers in the mid-1950's
<br />(Hubbs and Miller 1953, Minckley 1983), In the upper basin, its decline was also dramatic, and
<br />accelerated in the early 1960's with the construction of Flaming Gorge Dam on the Green River,
<br />Glen Canyon Dam on the Colorado River, and Navajo Dam on the San Juan River, all in 1963
<br />(Bestgen 1990), Altered river flows in these tributaries, habitat changes, and large numbers of
<br />non-native species adversely affected reproduction (Minckley 1983, Lanigan and Tyus 1973).
<br />
<br />The majority of razorback suckers in the upper basin are in Utah, but the largest numbers of wild
<br />adults are in Lake Mohave, where 60,000 adults were estimated in 1988 (Minckley et al, 1991),
<br />but only 25,000 adults were estimated in 1995 (Marsh 1995), Small numbers are also found in
<br />Lake Mead and Lake Havasu (Bestgen 1990), Razorback suckers are believed to be nearly
<br />elCtirpated from Grand Canyon. Ten adults were reported b~een Glen Canyon Dam and Pearce
<br />Feny in upper Lake Mead from 1944-90 (Valdez 1996). Of 2, 780 flannelmouth suckers captured
<br />in Grand Canyon during 1990-93, five fish were classified as morphologic intergrades with
<br />razorback sucker (Valdez and Ryel1997),
<br />
<br />In the upper basin, razorback suckers occur primarily in the Green River from Split Mountain to
<br />Green River, Utah(Tyusetal. 1982,1987; Tyus and Karp 1990), Numbers are greatly reduced
<br />downstream of that point. There are far fewer fish in the Colorado River, and recent
<br />investigations (Valdez and Williama 1990) yielded only one fish in the lower SO miles of the Green
<br />and Colorado rivers and upper Lake Powell, where numerous fish had been caught 10 years
<br />before (Bulkley and Persons 1982), Razorback suckers still inhabit Lake Powell as small numbers
<br />in the San Juan Ann and Dirty Devil inflow, as well as occasionally in fish SUIVeyS of the lake
<br />proper,
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