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The cyprinid genus Gila includes three historically sympatric species endemic to the Colorado River Drainage, i.e., G. robusta (roundtail chub), G. cypha (humpback chub) and G. elegans (bonytail). Roundtail chub are locally common and widely distributed throughout the Colorado River System, whereas humpback chub and bonytail are presently rare and have extremely restricted distributions (Behnke and Benson, Coop. Ext. Serv. Bull. 503A, Colorado State Univ., 1983; Lee et al., Atlas of North American freshwater fishes, North Carolina State Mus. Nat. Hist., Raleigh, 1980; Tyus et al., pp. 12-70 in Fishes of the Upper Colorado River System: present and future [W. H. Miller, H. M. Tyus, and C. A. Carlson, eds.], Am. Fish....
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ABSTRACT.-A survey of the Colorado River drainage in Colorado was made during the summer-fall of 1979-1981 to determine the distribution of larval Colorado squawfish (Ptychochielus lucius) and to relate their occurrence to the hydrological regime. Squawfish larvae were collected in the lowermost 31 km of the mainstem Colorado River in 1979-1981 and the lowermost 29 km of the Yampa River in 1980-1981. Larval squawfish were not found in collections from either the White or Gunnison rivers. Sampling effort appeared to have no effect on collection success, but collection success did appear to reflect reproductive success and/or larval survivorship. Estimates of spawning periods for the Colorado River range from as early...
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