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<br />
<br />VALDEZ AND MUTH
<br />
<br />1978). In the upper Colorado River subbasin, it
<br />was historically found as far upstream as Rifle, Colo-
<br />rado, on the upper Colorado River (Beckman
<br />1963); Delta, Colorado, on the Gunnison River
<br />(Burdick 1995); and Paradox Valley on the Dolores
<br />River (Lynch et al. 1950). In the Green River
<br />subbasin, it was reported as far upstream as Green
<br />River, Wyoming, on the Green River (Ellis 1914;
<br />Baxter and Simon 1970); Craig, Colorado, on the
<br />Yampa River; Rangely, Colorado, on the White
<br />River; and in the lower Price and Duchesne rivers
<br />(Tyus and Haines 1991; Cavalli 1999). In the San
<br />Juan River subbasin, Colorado pikeminnow were
<br />historically found upstream to Farmington, New
<br />Mexico, and the lower Animas River (Holden
<br />1999).
<br />Wild populations of Colorado pikeminnow are
<br />presently found only in the upper basin in about
<br />25% of historic range basin-wide (Figure 1). Adults
<br />occur in the Green River from Lodore Canyon to
<br />the confluence of the Colorado River (Tyus 1991;
<br />Bestgen and Crist 2000); Yampa River downstream
<br />of Craig, Colorado (Tyus and Haines 1991); Little
<br />Snake River into Wyoming (Marsh et al. 1991; Wick
<br />et al. 1991); White River downstream of Taylor
<br />Draw Dam, Colorado (Tyus and Haines 1991);
<br />lower 143 km of the Price River (Cavalli 1999);
<br />lower Duchesne River; upper Colorado River from
<br />Palisade, Colorado, to Lake Powell (Valdez et al.
<br />1982b; Osmundson et al. 1997, 1998); lower 54
<br />km of the Gunnison River (Valdez et al. 1982a;
<br />Burdick 1995); lower 2 km of the Dolores River
<br />(Valdez et al. 1992); and 241 km of the San Juan
<br />River from Shiprock, New Mexico, to the Lake
<br />Powell inflow (Jordan 1891; Koster 1960; Propst
<br />1999; Holden 1999).
<br />Colorado pikeminnow is adapted to warm riv-
<br />ers and requires uninterrupted passage and a hy-
<br />drologic cycle characterized by large spring peaks
<br />of snowmelt runoff and lower, relatively stable base
<br />flows. Adults are potadromous and may move up
<br />to 950 km to and from spawning sites in summer
<br />(Tyus and McAda 1984; Tyus 1990; Irving and
<br />Modde 2000). Juveniles and adults use deep, low-
<br />velocity eddies, pools, and runs, but move into
<br />flooded habitats and bottomlands during spring
<br />runoff (Tyus and McAda 1984; Valdez and
<br />Masslich 1989; Tyus 1990, 1991; Osmundson et
<br />
<br />al. 1995). Average fecundity is about 66,000-
<br />77,000 eggs/female (Hamman 1986), and females
<br />broadcast adhesive eggs over cobble bars during
<br />June-August at water temperatures of 160C or
<br />higher (Vanicek and Kramer 1969; Hamman
<br />1981). The eggs incubate for 90-121 hat 20-
<br />240C (Hamman 1981; Marsh 1985), and larvae
<br />drift up to 200 km to nursery backwaters where
<br />survival is critical to recruitment (Holden 1977;
<br />Tyus and Karp 1989; Haines and Tyus 1990; Tyus
<br />1991; Tyus and Haines 1991; Bestgen et al. 1997,
<br />1998; Converse et al. 1999). Young Colorado
<br />pikeminnow consume woplankton and midge (chi-
<br />ronomid) larvae (Vanicek 1967; Jacobi and Jacobi
<br />1982; Muth and Snyder 1995), and piscivorous
<br />adults eat soft-rayed native and nonnative fish
<br />(Osmundson 1999), as well as a variety of insects
<br />and animals, including Mormon crickets Anabrus
<br />migratorius (Tyus and Minckley 1988), mice, birds,
<br />and rabbits (Beckman 1963).
<br />
<br />Humpback Chub
<br />
<br />Humpback chub is an endemic cyprinid of the Colo-
<br />rado River system with an evolutionary history of
<br />about 3 million years (Miller 1946, 1955; Minckley
<br />et al. 1986). Maximum size is 480 mm TL and 1,165
<br />g (Valdez and Ryel1997), and maximum age is over
<br />20 years (Hendrickson 1993). The body is deep and
<br />laterally-compressed, tapering abruptly to a narrow
<br />caudal peduncle with a deeply forked tail fin and
<br />large falcate paired fins. Head length divided by
<br />caudal peduncle depth is usually less than 5.0, com-
<br />pared to greater than or equal to 5.0 for bony tail,
<br />and greater than or equal to 3.0 for roundtail chub
<br />(Minckley 1973). Introgressive hybridization may
<br />be part of their evolutionary history (Dowling and
<br />DeMarais 1993), and high phenotypic plasticity
<br />exists with morphologic intergrades in all sympatric
<br />populations of humpback chub, bony tail, and
<br />roundtail chub (Holden 1968; Holden and
<br />Stalnaker 1970; Smith et al. 1979; Valdez and
<br />Clemmer 1982; Kaeding et al. 1990; Wick et al.
<br />1991; McElroy and Douglas 1995; Douglas et al.
<br />1989, 1998). Humpback chub was listed as endan-
<br />gered in 1967 (32 FR 4001) and protected by the
<br />ESA in 1973 (39 FR 1175), with critical habitat
<br />designated in 1994 (59 FR 13374). A recovery plan
<br />
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