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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numbers ofYOY small mouth bass were collected in each year at Duffy with similar counts

between years with higher and lower runoff flows. Hawkins et al (1997) reported the

occurrence of nonnative fish were fairly rare in the Little Snake River and attributed this to

highly variable physical factors such as flows, temperature and turbidity. Hawkins felt the

extreme low flows he observed could be beneficial to the native fish population because

nonnative fish were not common in his study sites. His conclusions for the Little Snake are

not consistent with results of this study. In the Yampa River species composition was similar

in the years with low base flow compared to the other years indicating non-native fish survival

is comparable to native fish under flows experience between 1998 and 2000. The data do not

indicate that peak or minimum flows have hampered or repressed abundance of most

nonnative fish species in the Yampa River.

The Duffy station, because of its low composition of native fish, does not appear to be

a suitable site for making inferences about habitat use by native fIsh. When the Duffy study

site was selected it was believed to be representative of the Yampa between Juniper and Craig

for both fish and habitat composition. However it appears that competition and predation are

influencing population structure at this site (and river reach) independent of habitat

composition. Because of this it was necessary to add a new site on the Yampa River, one with

a higher native fish composition. So in 2000 a site was added at Lily Park.

Species composition was more variable between years for fish under 15 em for the

1998 to 2000 period (Table AZ). Sand shiners were the most common small fish at Sevens in

all three years, but small mouth bass was most common at Duffy. In the year 2000, there was

noticeably fewer native species in the sample, only 3% at Sevens and 6% at Duffy. Very few

speckled dace and mottled sculpin, both species generally associated with rime habitats, were

observed or collected at both stations in 2000 compared to 1998 and 1998. This indicates

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