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Page 23 humpback chub (Gila cypha) and bonytail (G. elegans) in Desolation and Gray Canyons of the Green River has been postulated by many observers (Douglas et al. 1998, Kaeding et al. 1990, Valdez and Clemmer 1982). Whether biologists and agencies recognize two species, two species ~ and a hybrid form, three species, or some other combination has implications for how the fish are managed. Because roundtail chub are congeners with humpback chub and bonytail, the potential for hybridization between the species exists, though it has not been as well documented as humpback chub/bonytail hybrids. Valdez and Clemmer (1982) have suggested that hybridization is a result of dramatic environmental changes, while Dowling and DeMarais (1993) suggest that ~ hybridization among these species has occurred continually over geologic time, providing additional genetic variability. Barriers to hybridization among some Gila species may illustrate that it is a paraphyletic genus (Coburn and Lavender 1992 and references therein). Roundtail chub in the Gila River drainage of New Mexico and Arizona was recently divided into three species, G. robusta, G. intermedia, and G. nigra through genetic analysis (Minckley and ~ DeMarais 1990). Additional investigation of these relationships and resulting offspring is needed and may affect future conservation and management actions for roundtail chub and other Gila species. The Virgin chub (G. seminuda) found in the Virgin River has been historically treated as a ~ subspecies of roundtail chub (Maddux et al. 1995) and is thought to have originated through hybridization between the bonytail and the Colorado roundtail chub (Maddux et al. 1995, Sigler and Sigler 1996 and references therein). In 1993, taxonomic revisions were accepted, and the Virgin chub was asserted species- status as G. seminuda (Maddux et al. 1995). It is currently listed as endangered under the federal Endangered Species Act. ~ Roundtail chub presently exist in the United States only in the Gila River Basin, the Little Colorado River Basin, the Bill Williams River Basin, and the Upper Colorado River Basin, including the Green River Basin. Lee et al. (1980) also recorded occurrences in northern Mexico, which was anecdotally confirmed by personal communications in 2001 with S. Contreras- Balderas (Bioconservacion A.C., Monterrey, Nuevo Leon) and A. Varela-Romero (Universidad ~ de Sonora, Hermasillo). In Utah, roundtail chub occur in the Green and Colorado rivers and major tributaries of the two. Historically, roundtail chub were found in all of the state's major drainages, though abundance information was not recorded (see Figure 2-6) (Utah Division of Wildlife Resources 2001). r Roundtail Chub Status Review General Historical literature suggests that roundtail chub were common to all parts of the Colorado River ~ Basin up to the 1960's (Jordan and Evermann 1902, Minckley 1973, Sigler and Miller 1963). They are believed to have occurred in most faster flowing rivers and streams below 2,300 meters elevation (Bezzerides and Bestgen 2002). While they continue to occupy a number of rivers and streams in the upper basin, declines in numbers and relative abundance have been observed in many of these locations (Bezzerides and Bestgen 2002, Brunson and Christopherson 2003, ~ Platania 1990).