WSP12249

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 6/1/2004
• Author: CDOW
• Title: Riverine Fish Flow Investigations 2004
• Water Supply Pro - Doc Type: Publication

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COLORADO RIVER

/ 5-,vlile Reach (Corn Lake and CIi(Ion)

Two adjacent study sites were used in the IS-Mile Reach for the instream flow study
based on prior research (Anderson and Stewart 2003). Clifton is the upstream site and Com
Lake the downstream site. Fishery and habitat features (geomorphic differences) of these
two sites were both compared, The objective of this study was to compare fish abundance
between years of different base flows. Combining data from both sites was more useful for
this study, since a single long station (4.2 kIn) and larger sample size was believed to
improve statistical sensitivity to changes in the fish population between years.

The baseline years for the IS-Mile Reach were 2000 and 2001 when Summer and
early Fall flows were near 900 cfs, Flows in 2002 were less than 300 cfs for 90 days and less
than 100 cfs for 40 days. Flows were above 1,000 cfs during sampling in September 2003.
Subtle changes were observed in species composition for fish over 15 cm in 2003 compared
to pre-drought years, Several of the changes were consistent with those observed during the
first year of the Yampa River's dry cycle,

For tish over IS cm, native fish were 75% of the catch in 2000, 77% of the catch in
2001, and 76% of the catch at Com Lake in 1999 (Table 16), In 2003 native fish comprised
66% of the catch for fish over 15 cm (Table 16).

During the baseline years, the two most common species were flannel mouth sucker
averaging 36% and bluehead sucker averaging 35%. In 2003 flannelmouth composition was
33% and bluehead was 28%, Bluehead sucker was the species with the largest negative
change in 2003 at minus 20%. Flannelmouth was minus II %. Roundtail chub comprised
about 5% of the catch for 2000,2001 and 2003 (Table 16). Endangered fish were less than
1 % of the catch in all years.

Carp composition in 2003 was very similar to all years sampled at 12% (Table 16),
Channel catfish composition in 2003 was 8%, an increase of 52% from baseline years (5%).
The composition of white sucker and its hybrids was 9%, which was about double the
baseline figure (Table 16), The largest increase in composition (175%) was for centrarchids,
Centrarchid composition in 1999,2000 and 2001 was about I %, These fish were mostly
collected in backwaters and were less than 15 cm in length. Smallmouth bass were very rare
in the baseline years with only zero to two individuals per year, In 2003 the number of
small mouth bass> IS cm increased to 45, The increased presence of smallmouth bass over
15 cm accounted for centrarchids increasing to 3% of the population in 2003.

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