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<br />Area Manager
<br />DRAFT
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<br />On March 14, 1989, the Service was petitioned to conduct a status review of the razorback
<br />. ~ ~ ...." 1 1 L_ -----..:I--~__..._.J____...1______...I~........I""_".+.:n...l.r."lQ
<br />SUCKer. ~uDsequen(JY, me razoroal.:Jt SU{,;K.tl W~ uC::.il2::;Uc1U;U 4:) l;;;J1UQJJ!:.,",H..u UlJU,,",J. u. uu...... . .......
<br />published on October 23,1991 (56 FR 13374). The fmal rule stated that "Little evidence of
<br />natural recruitment has been found in the past 30 years, and numbers of adult fish captured in the
<br />last 10 years demonstrate a downward trend relative to historic abundance. Significant changes
<br />have occurred in razorback sucker habitat through diversion and depletion of water, introduction
<br />of nonnative fishes, and construction and operation ofdams"(56 FR 13374). Recruitment of
<br />razorback suckers to the population continues to be a problem.
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<br />Critical habitat was designated in 1994, within the I DO-year flood plain of the razorback sucker's
<br />historical range in the following area of the upper Colorado River (59 FR 13374).
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<br />New Mexico, San Juan County; and Utah, San Juan County. The San Juan River from the
<br />Hogback Diversion in T, 29 N., R. ]6 W., section 9 to the full pool elevation at the mouth of
<br />Neskahai Canyon on the San Juan arm of Lake Powell in T. 41 S., R. 11 E., section 26.
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<br />The primary constituent elements of critical habitat are the same as those listed for pikeminnow,
<br />described above.
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<br />Life History
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<br />McAda and Wydoski (1980) and Tyus (1987) reported springtime aggregations of razorback
<br />suckers in off-channel habitats and tributaries; such aggregations are believed to be associated
<br />with reproductive activities. Tyus and Kaxp (1990) and Osmundson and Kaeding (1991)
<br />reported off-channel habitats to be much warmer than the main stem river and that razorback
<br />suckers presumably moved to these areas for feeding, resting, sexual maturation, spawning, and
<br />other activities associated with their reproductive cycle.
<br />
<br />While razorback suckers have never been directly observed spawning in turbid riverine
<br />environments within the upper Colorado Basin, captures of ripe specimens, both males and
<br />females, have been recorded in the Yampa, Green, Colorado, and San Juan Rivers (Valdez et aI.
<br />1982, McAda and Wydoski 1980, Tyus 1987, Osmundson and Kaeding 1989, Tyus and Karp
<br />1989, Tyus and Karp 1990, Osmundson and Kaeding 1991, Platania 1990, Ryden 2000b).
<br />Sexually mature razorback suckers are generally collected on the ascending limb of the
<br />hydrograph from mid-April through June and are associated with coarse gravel substrates. Both
<br />sexes mature as early as age four (McAda and Wydoski 1980). Fecundity, based on ovarian egg
<br />counts, ranges from 75,000-144,000 eggs (Minckley 1983). Several males attend each female;
<br />no nest is built. The adhesive eggs drift to the bottom and hatch there (Sublette et a!. 1990).
<br />Marsh (1985) reported that percentage egg hatch was greatest at 20'C (68"F) and all embryos
<br />died at incubation temperatures of 5, 10, and 30'C (41, 50, and 86'F).
<br />
<br />Because young and juvenile razorback suckers are rarely encountered, their habitat requirements
<br />in the wild are not well known, particularly in native riverine environments. However, it is
<br />assumed that low-velocity backwaters and side channels are important for YOY and juveniles, as
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