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from yeaz to yeaz with varying flow scenarios, although cross-channel sampling was conducted only in 1992 during that study. We believe that the larger volume of water present in the Colorado River than the Yampa River may affect distribution of larvae in the water column. The Colorado River at the Cisco gage carved approximately 5 times the volume of water the Yampa carved in 1992 (based on average July flow), and from 8 to 26 times as much for the other 4 years of the study. If the assumption of even distribution throughout the water column is in error, the estimated catch rate in # fish/hour corrected for river volume could be vastly over or under estimated since the percent of total river volume sampled is quite small, from 0.0002% to 0.002%. Based on Yampa River results, dawn, near-shore sampling is sufficient to determine relative abundances and peaks in drifting pikeminnow larvae, but perhaps not to estimate the total numbers of pikeminnow larvae produced. Nevertheless, we have used this method in this report to make our data comparable to the concurrent Green River larval drift results (Bestgen et al. 1998). The post-hatch ages of the pikeminnow were calculated from total lengths, using formulae developed by Haynes et al. (1985) and Muth (1990) (Appendix A2), which result in slightly different ages. However, the Haynes et al (1985) formula was used for analysis. Spawning dates were estimated by adding six days to the post-hatch ages (Bestgen et al. 1998, Bestgen and Williams 1994). Water temperatures were taken by the crews each morning at the drift sites. Daily water temperatures are also recorded by the USGS at each gage. Temperatures were thought to affect spawning behavior more than drift behavior. The USGS gage data might more accurately characterize the main channel temperature, which affects spawning behavior, than near-shore temperatures at dawn. Therefore the degree day accumulations and the date the river reached 18°C each year used in analyses were calculated from the USGS data. Degree day accumulations were estimated from January 1 through each month, and to the estimated onset of spawning. The strength of association between the variables of flow (magnitude of peak, and average monthly flows), temperature (degree day accumulation and date the water temperature reached 18°C), and collections of Colorado pikeminnow and non-native cyprinids (catch rates and total transport abundance) were tested using Peazson's correlation coefficients. The correlations between temperature, length of growing season, total length of Colorado pikeminnow in the fall, and overwinter survival were tested, also using Peazson's correlation coefficients. The nature of the data did not lend itself to more rigorous analysis. RESULTS Species composition and relative abundance Five native and ten non-native fish species or taxa commonly found in the Colorado River in this azea were collected in the drift net samples (Appendix B). Native species collected include the endangered Colorado pikeminnow, as well as bluehead sucker (Catostomus discobolus), flannelmouth sucker (Catostomus latipinnis), and speckled dace (Rhinichthys osculus). The three species of the native Gila taxon (presumably mostly roundtail chub G. robusta) were not differentiated as larvae, and were counted as one. The most abundant non- native species were the three common cyprinids: red shiner (Cyprinella lutrensis), sand shiner 3