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returned to within 0.5 km of the original capture location (Valdez and Carothers 1998). The results of this study showed little movement for both species, but less for roundtail than humpback chub. Humpback chubs persisted in the system longer averaging 575 days between captures; roundtails averaged 447 days between captures. A limitation of the present mark-recapture study was that all the effort was confined to Westwater Canyon, which obviously biased results toward sedentary individuals. Other Recovery Program efforts (Back Rocks sampling 16 km upstream of Westwater and Interagency Standardized Monitoring spring electrofishing 32 km downstream) have recaptured chubs tagged in Westwater Canyon on a very infrequent basis. As mentioned earlier, immediately below the rapids of Westwater Canyon, chubs become very scarce, i.e., we defined the lower terminus of the Westwater chub populations. From the recapture information it is clear some adult chubs, roundtail and humpback, persist in Westwater canyon for at least five years. However, it is our feeling that the low recapture rates experienced in this study could be explained by either a very large population or a dynamic population as opposed to a mobile one. The humpback and roundtail chubs that were recaptured multiple times displayed no movement including a female roundtail (7F7BIIOB29) collected on five occasions (at the Hades Bar site) over the course of 1099 days. As alluded to earlier, strong densities of juvenile chubs were found three out of four years and yet the long term monitoring data suggests the density of adult chubs in the canyon remains relatively constant. There is likely significant replacement of adults, particularly roundtail chubs, occurring in Westwater Canyon on an annual basis. Since this study, three more incidences of chub moving from Westwater Canyon upstream to Black Rocks have been reported bringing the total to four. In 1997, Colorado Division of Wildlife crews recaptured 2 humpback chubs (one originally tagged at RK 198.6 in 1995 and one tagged at RK 194.4 in 1993) and a roundtail (originally tagged at RK 192 in 1993). All of these fish were <_ 230 mm TL at the time of initial capture, what we would consider young adults. There may be more communication between these two populations than originally suspected; this aspect of chub behavior will be further monitored as the number of tagged individuals in the system increases. A series of tighter population estimates would provide valuable information as to population dynamics in Westwater Canyon. To be effective, we would need to increase the tagging effort and compress the time between sampling passes. The approach the USFWS took estimating Colorado pikeminnow population size on the Colorado River (Osmundson and Burnham 1996) would be the preferred sampling protocol. In addition, radio telemetry would likely shed light on the movement issue as well as the differential catch rates of native chubs reported between the summer and fall. CONCLUSIONS Yoy ^ Chubs spawned each year of the study as evidenced by the collection of YOY in each study subreach. ^ In three of four years of analysis it appears roundtail chubs spawned earlier than humpback based on a comparison of back calculated hatch dates above the canyon vs within - in part describes reproductive isolation of native Gila spp. ^ Earliest chub hatching date (Julian) (as estimated through back calculation) was positively correlated (RZ = .988; p<0.05) with pre-peak flows in excess of 6000 cfs and negatively correlated (RZ = .98; p=0.087) with pre-peak degree days > 10°C. Chubs spawned on the 27