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4 INTRODUCTION As a consequence of documented declines in numbers and ranges of Colorado squawf ish and humpback chubs, these species have been listed as endangered by both the federal government and the State of Colorado. Accordingly, recovery plans have been approved for both species. Both plans recognize a number of factors which appear to be responsible for the endangered status of these species, including habitat alterations (i.e. river modifications, diversions, withdrawals, etc.), competition from nonnative species, and, in the case of humpback chubs, hybridization with congeners. Since 1977, the Colorado Division of Wildlife has been investigating the status of these species via systematic sampling in the Colorado, Yampa, White, and Gunnison Rivers. Recently, studies have been conducted in cooperation with the U.S. Fish and Wildlife Service (Colorado River Fisheries Project). As a result of these efforts, the distribution, relative abundance, and status of these species within the State of ` Colorado have been documented and described (Wick et al., 1981; Miller et al., 1982a; Miller et al., 1982b). In Colorado, squawf ish are apparently restricted to the lower and middle reaches of the Colorado, Yampa, Gunnison, and White Rivers and to a section of the Green River near its confluence with the Yampa in Dinosaur National Monument. Reproduction has been documented in a reach of the Colorado River west of Grand Junction (Mesa County) and in a reach of the Yampa River in Dinosaur National Monument (Moffat County). Humpback chubs appear to have a more restricted distribution, reaching their greatest abundance in the Black Rocks area of the Colorado River. -Six humpbacks collected in 1981 in the Green-Yampa system in Dinosaur National Monument and one collected in Cross Mountain Canyon in 1980 suggests the presence of a small population in this area. Although evidently ripe humpback adults have been observed, particularly at Black Rocks, evidence of successful reproduction, via the collection of larval forms, has not been documented since adaquate features for the differentiation of humpback chubs from the more common roundtail (G. robusta) have not been developed. Additionally, considerable genetic variation appears to exist in the genus Gila in the Upper Colorado River as a consequence of sympatry between the humpback, roundtail, and the apparently extinct bonytail (G. elegans). Although the "pure" adult forms may be readily identified, "intergrades" and/or "hybrids" are frequently encountered which cannot be readily assigned to a specific taxon. The problem is compounded relative to the identification of young, since adequate differentiation between the "pure" forms has not been accomplished, nor has intergradation or hybridization been addressed. The analysis of larval/juvenile squawf ish and humpback chubs, therefore, is an essential aspect of the overall research project. This progress report includes a description of overall field/laboratory methods and a preliminary summary of data collected during the period January 1, 1981- June 30, 1982.