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this, its original distribution is not known. The humpback chub was <br />listed as endangered on March 11, 1967. <br />19 <br />Until the 1950'x, the humpback chub was known only from Grand Canyon. <br />During surveys in the 1950's and 1960's humpback chub were found in <br />the upper Green River including specimens from Echo Park, Island Park, <br />and Swallow Canyon (Smith 1960, Vanicek et al. 1970). Individuals <br />were also reported from the lower Yampa River (Holden and Stalnaker <br />1975b), the White River in Utah (Sigler and Miller 1963), Desolation <br />Canyon of the Green River (Holden and Stalnaker 1970) and the Colorado <br />River near Moab (Sigler and Miller 1963). <br />Critical habitat was designated in 1994 within the humpback chub's <br />historical range in the following sections of the Upper Colorado River <br />(59 F.R. 13374). The primary constituent elements are the same as <br />those described for the Colorado pikeminnow. <br />Utah. and ('o m y• and ColOradO. MPaa rolinty. The Colorado River <br />from Black Rocks in T. 10 S., R. 104 W., section 25 (6th Principal <br />Meridian) to Fish Ford in T. 21 S., R. 24 E., section 35 (Salt <br />Lake Meridian). <br />tTr~~h,f:arf; el d nd Ran Jvan C`rnm i a , <br />Brown Betty Rapid in T. 30 S., R. 18 <br />Meridian) to Imperial Canyon in T. 31 <br />(Salt Lake Meridian). <br />The Colorado River from <br />E., section 34 (Salt Lake <br />S., R. 17 E., section 28 <br />Today the largest populations of this species occur in the Little <br />Colorado and Colorado Rivers in the Grand Canyon, and in the Black <br />Rocks area of the Colorado River. Other populations have been <br />reported in Westwater and DeBeque Canyons of the Colorado River, <br />Desolation and Gray Canyons of the Green River, Yampa and Whirlpool <br />Canyons in Dinosaur National Monument (USFWS 1990b). One individual <br />was recently captured in the Gunnison River (Burdick 1995). <br />In general, the existing habitat has been modified to the extent that <br />it impairs essential behavior patterns, such as breeding, feeding, and <br />sheltering. <br />It is known that these chubs spawn soon after the highest spring flows <br />when water temperatures approach 68° F (Kaeding et al. 1990; Karp and <br />Tyus 1990a; USFWS 1990b). The collection of ripe and spent fish <br />indicated that spawning occurred in Black Rocks during June 2-15, <br />1980, at water temperatures of 11.5° to 16° C; in 1981, spawning <br />occurred May 15-25, at water temperatures of 16° to 16.3° C (Valdez et <br />al. 1982b). Humpback chub spawned in Black Rocks on the Colorado <br />