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I I I I I I I I I I I I I I I I I I I indicate how much of the observed differences in fish populations are explained by physical habitat availability. COLORADO RIVER Total fish density was estimated at 3,962 per km at Corn Lake in 1999 and 3,417/km in 2000 (Table 6). Total fish density was significantly different at the Com Lake station between 2000 and 1999 (Table 7). The estimates for both bluehead and flannel mouth sucker were significantly less in 2000 (1182 and 999 per km) compared to 1999 (1573 and 1550 per km). Density estimate for roundtail chub were higher in 2000 (357/km) than in 1999 at 192/km and is significant at the 0.05 level (Table 7). Also the estimate for carp and catfish increased in the lower flow year of2000. The only estimate not significantly different between the two years was for white sucker. As was suggested for the Yampa River, the differences in density estimates between years at Corn Lake could be due to the different flow conditions between years. Mean flow in August 1999 was 1800 cfs and in August 2000 it was 800 cfs (Figure 6). Estimates for bluehead and flannel mouth, species that utilize run and rime habitats, were less, but species that primarily use pool habitats (chub, carp and catfish) were higher in the years with low flows. This shift in species abundance is consistent with a shift in habitat conditions that result from lower flows observed in 2000. More detail will be given to this issue in the final report when the habitat analysis is completed. Also fish data collected in 2001 will help confirm if the decrease in bluehead and flannel mouth densities in 2000 reflects a drop in carrying capacity of the river as opposed to fish relocating to other reaches as was observed on the Yampa River. However it is believed the stations may be long enough to contain local movements, a total of6.8 km shocked in 2000 for both stations. 37