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<br /> <br />INTRODUCTION <br />The Colorado River Basin has the highest percentage (87%) of <br />endemic primary riverine fishes of any North American river basin <br />(Miller 1959). A total of 55 forms has been reported from the <br />Upper Colorado River Basin, of which 13 are native and eight are <br />endemic (Tyus et al. 1982). Among these native forms, four are <br />federally listed as endangered (Colorado squawfish, Ptychocheilus <br />ucius, humpback chub, Gila cypha, bonytail, Gila elegans, and <br />Kendall Warm Springs dace, Rhinichthys osculus thermalis) and two <br />are federal Notice of Review (roundtail chub, Gila robusta and <br />razorback sucker, Xyrauchen texanus) as candidates for listing. <br />The species currently receiving the most study are the Colorado <br />squawfish, species in the genus Gila (bonytail, humpback chub, <br />and roundtail chub) and the razorback sucker. These five taxa <br />comprise the target species, as defined in this report. <br />In the initial (1987) phase of the present survey, we were <br />able to document the occurrence of Colorado squawfish in the San <br />Juan River of New Mexico for the first time since 1961, and <br />roundtail chub for the first time since 1977. Additionally, we <br />found young-of-year (YOY) of both species, thereby confirming <br />their successful reproduction in the San Juan River in New <br />Mexico. To date, we have not collected or observed razorback <br />sucker, bonytail, or humpback chub in the New Mexico portion of <br />the San Juan River.