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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the added situation of intense competition with a larger population of white sucker and white

sucker X bluehead sucker crosses.

The length frequency histograms were very similar for flannel mouth sucker between

the three years at Duffy and Sevens on the Yampa River. Flannelmouth are rare below 43 cm

at Sevens (Figure A 7) and absent at Duffy (Figure A8). In contrast flannel mouth length

frequency approximates a normal distribution at Lily Park (Figure A9), with over half the fish

below 43 cm (mean = 41.5 em). On the Dolores River the majority offish are small, under

28 cm, and large adult fish are uncommon (Figure AIO). Flannelmouth from the Colorado

River at Com Lake (Figure All) and Clifton (Figure A12) have an size groups represented

and large adults range in size from 37 em to 55 em.

The environmental factors that appear to effect bluehead sucker size distribution also

apply to flannel mouth, since both species exhibit the same pattern between rivers. The

Colorado River appears to represent a flannel mouth sucker population with abundant habitat

and a lack of predation and competition. Their size distribution in the Colorado River ranges

from 7 to 55 em with modes representative of all age groups. It is believed that in the

Colorado River both flannel mouth and bluehead sucker are at 'carrying capacity' of the

physical habitat. On the Dolores River the few numbers of flannetmouth adults relative to

juveniles is apparently a result of pool habitat availability and/or very low productivity (forage

potential). A predator line at Sevens and Duffy is apparent in all three years of sampling

those sites and few flannel mouth are present below 43 cm. However, at Lily Park

flannel mouth become rare below 28 em. This could suggest that pike large enough to prey on

fish over 30 em are less common at Lily Park, or that flannel mouth recruitment of juveniles is

much higher at this site. Duffy has a very large population of white-flannel mouth sucker

hybrids, strongly indicative of intense competition between native suckers and white sucker

hybrids. The size structure of flannel mouth sucker in the Yampa River at Sevens and Duffy is

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