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reproduction in the lower Green River includes the collection in 1991 of two juveniles (36.6 and 39.3 mm TL) from a backwater area (RK 89.5) downstream of the San Rafael River confluence in Middle Stillwater Canyon (Gutermuth et al.-1994). Fifteen larvae (13-16 mm TL) were captured at the Colorado River inflow to Lake Powell in 1993 (Muth and Wick 1997) which were most likely produced in the lower Green River. Thus, the occurrence of razorback sucker larvae and juveniles suggest that reproduction and limited recruitment is occurring in the lower Green River and suggests the presence of an adult spawning aggregation. In the Colorado River, razorback sucker populations are now nearly extirpated (Burdick 1992; Holden et al. 1981; Nesler 1999). A single razorback sucker was collected in the Colorado River during ISMP activities in 1988 (McAda et al. 1994a). It was the only razorback sucker collected from the Colorado River between 1988 and 1997 during ISMP activities. Three razorback suckers were collected near RK 211 in 1993 (D. Osmundson, Fish and Wildlife Service, unpublished data). Nesler (1999) has developed a stocking plan for razorback sucker in the portion of the Colorado River that lies within the state of Colorado. Factors Limiting Natural Reproduction Poor survival of early life stages and limited recruitment into the adult population has resulted in the precarious existence of razorback suckers in the Green River (Muth et al. 1998). Although there is evidence of reproduction in the middle and lower Green River populations, natural survival offish beyond the larval stage is low and wild stocks are composed of senescent fish that continue to decline in abundance (Muth et al. 1998). Limited access to floodplain habitat due to loss and modification and predation from nonnative fishes are the principle causes of early life stage mortalities (Hamilton 1998, Hawkins and Nesler 1991, Lentsch et al. 1996b, Maddox et al. 1993, Tyus and Saunders 1996, USFWS 1997). The Recovery Implementation Program (RIP) for Endangered Fish Species in the Upper Colorado River Basin has begun major efforts in restoring natural habitats and controlling nonnative fish. However, with the limited number of adults in the population, augmentation is necessary to take advantage of these management actions. Habitat enhancement and reducing nonnatives allow for the expansion of razorback sucker. By stocking razorback suckers, the opportunity for naturally produced larvae and stocked juveniles to utilize these open floodplain habitats is possible. The RIP currently conducts an Interagency Standardized Monitoring Program (ISMP) (USFWS 1987). In 1986 the ISMP began monitoring young-of--year, subadult, and adult Colorado pikeminnow (Ptychocheilus Lucius), and adult humpback chub (Gila cypha) in river reaches important to the endangered fishes (McAda et al. 1994a). Information on other rare or introduced species was also collected when they were encountered. The number of razorback suckers encountered has decreased each year since the beginning of monitoring in 1986 (Table 1). According to ISMP data (McAda et al. 1994a, 1994b, 1995, 1996, 1997) and Utah Division of Wildlife reports (Day and Crosby 1996; Brunson et al. 1997; Chart et al, 1998), razorback sucker populations appear to be declining in the Green River and are rare in the other rivers based on the decreasing numbers of adults encountered and apparent lack of recruitment. In 1995, a razorback sucker augmentation stocking program was initiated (Wydoski 1996). The plan called for stocking 1,000 fish per year for three years. The objective was to increase the number of adults from approximately 500 to 1,000 individuals by the year 2001. The program met stocking goals in 1995 and 1996. However, fish were not stocked in 1997 due to a lack of equal size lots to stock and timing of the event. 3