WSP07697

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 7/1/2001
• Author: CDOW
• Title: Riverine Fish Flow Investigations 2001
• Water Supply Pro - Doc Type: Publication

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Yampa River, but lacked small fish. In Sevens and Duffy the size distribution would probably

be more similar to the Colorado River if non-native predators and suckers were not present.

Small white sucker were present at Sevens (Figure A19) and Duffy (Figure AZO)

indicating this species is better adapted to avoid predation than native suckers. Most of the

white sucker on the Colorado River (Figures AZI and AZ2) were taken from slow backwater

habitats and also since they are uncommon, this species is probably not a significant

competitor for resources with native suckers. The white-flannel mouth cross size structure on

the Yampa is comprised oflarge individuals (Figures AZ3 and AZ4), another indication that

small fish have poor survival due to predation in the upper Yampa. Both the white-

flannel mouth and the white-bluehead sucker crosses (Figures A 27 and AZ8) on the Yampa

attain larger sizes than the pure flannelmouth and bluehead sucker, which could mean the

hybrid suckers have an advantage in regard to competition and avoiding predation.

The size structure for carp mimics the generalized pattern described for other species

in the Yampa River. Carp were few and very large (62 to 78 em) at Duffy (Figure A32), more

common and smaner at Sevens (45 to 68 em) (Figure A31) and even more common and

smaller stin at Lily Park (33 to 52 cm) (Figure A33). Except for one YOY, carp in the

Dolores River were between 49 and 62 em. Most of the small carp (less than 30 em) in the

Colorado River were taken from backwater habitats, but large carp were very common in the

main channel. This suggests more and better carp habitat is found in the Colorado River than

is found on the Yampa and Dolores Rivers. In fact many carp in the Colorado River were

sampled near outlets of sewage treatment ponds. The accumulated deposits at one such spot

seemed very attractive as carp completely filled a small backwater. Also many carp in the

Colorado River were found in shoreline habitat with overhanging trees that provided dense

cover. Both conditions (enrichment and dense cover) were rare in the Yampa and Dolores

Rivers.

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