WSP07697 - Laserfiche WebLink

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SUMMARY Electrofishing results in 2000 for species composition and size structure offish over 15 em were similar and consistent with earlier years at all stations. But total fish density was somewhat lower than in earlier years (1998 and 1999) on the Yampa River and also lower at the Com Lake station on the Colorado River. It was suggested that the lower fish abundance in 2000 could be an effect of the lower base flows experienced that year. A third station was added to the Yampa River in 2000 at Lily Park. This site had grossly different fishery characteristics compared to Sevens and Duffy stations. The observed differences in species composition, density, and sizes between Yampa sites appear to be more related to differences in meso-habitat availability (gradient, substrate particle size, rime/run ratios) than to differences in predatory pressure, temperature or water quality. Large differences were observed between the Yampa and Colorado River fisheries. The Colorado River has a different species composition, size structure and much higher total fish and native fish densities. Large predator fish were rare in the 15-Mile Reach and all size and age-groups were present. In contrast predator fish are common in the Yampa and obviously impacts that community. On the Yampa there is a lack offish under 30 cm, and higher mean lengths for virtually all species at Duffy and Sevens. Even at Lily Park where flannel mouth sucker were abundant, none were sampled under 28 cm. Habitat analysis completed on the Duffy and Com Lake sites found very large difference in habitat composition between these two locations. Stream width and therefore total wetted area (habitat potential) at most flows of interest were higher at Duffy than at Com Lake. Habitat diversity peaked at 1400 cfs at Com Lake and 180 cfs at Duffy. This is a function of greatly differing channel morphology between the sites. Most of the differences in 46 I I I I I I I I I I I I I I