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chub represent the only universally recognized pure population of bonytail. During the duration of this study no chub thought to closely re- semble bonytail were captured from the main Colorado River or its trib- utaries. In the Green, the taxonomic picture was very confused with a few relatively typical representatives of each species being collected along with a sizeable number of atypical intergrades. There was a relatively prominent concentration of Gila spp. located at the lower end of Coal Creek Rapid that initially was thought to be composed of a significant number of G. elegaris. Extensive examination of 19 specimens collected from this population has provided only one individual fish that conformed with all criteria established by Smith et al. (1979) for bonytail chub. Our studies did not devulge any significant numbers or populations of bonytail chub in the Upper Colorado River Basin. Migration and Movement Very little information on any life stage of the bonytail chub is available in the literature or from this study. Because of the ex- tremely precarious status of the bonytail chub in the wild, this species is considered to be on the edge of extinction. The only bonytail chub recaptured in this study was one of two chub recaptures in Gray Canyon. The recaptured fish was at the same site it had been captured 45 days previously. This individual fish was sedentary during this interval, but little can be said from this one observation concerning migration and movement. We do know that, based on captures in Lake Mohave over the past few years, W.L. Minckley and others have caught adult spawning bonytail chub at one fairly specific location of the reservoir (Hamman, 1981). Habitat Selection Collections of more specimens in the wild will be needed before habitat selection can be determined for the bonytail. The few fish captured during this study occurred in the deep swift canyon areas in association with both humpback and roundtail chubs. Although a few large adult bonytail chub still occur in Lakes Mohave and Havasu, these areas are not considered typical habitat for this species. Limiting Factors _Temperature - The bonytail requires and prefers certain temperatures. The temperature required for spawning of bonytail chub has been reported to be approximatelq 18°C (Vanicek and Kramer, 1969). Ten bonytail chub taken in Lake Powell in 1965 selected water temperatures that ranged from 16.6°C at 70 ft to 25°C at one foot of depth. The weighted mean