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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1986, This suggested that roundtail chub had adjusted to long term low base flows by
maintaining small body size,

The fact that native fish maintained a remnant population given habitat conditions
that occur during long-term low-base flows indicated this population could respond
positively if flow conditions improved, The Dolores River data suggested low flows would
be much less problematic on the Yampa River if nonnative fish were not present in the
system. Also, the situation on the Yampa River suggested that the native fish population of
the Dolores River was susceptible to replacement by nonnative species such as green sunfish
and small mouth bass,

SUMMARY

Five years of fish composition, density, biomass and size structure data were
summarized at Sevens and DulTy on the Yampa River. The first two years, 1998 and 1999,
were identified as baseline population data, since these years had normal Summer and Fall
t10w conditions. The years 2000 and 2001 were the first two years of reduced base flows on
the Yampa River. Very low flows occurred during 2002. Native fish density and biomass
were reduced at all sites in 2003 compared to baseline years. Small mouth bass and white
sucker composition were increased in 2003 at both sites compared to the baseline years,
Speckled dace, mottled sculpin and bluehead sucker were eliminated or much reduced.
Flannelmouth sucker were noticeably reduced in 2003 compared to the baseline years.

Three years of fish population data were presented for the Lily Park site on the
'{ampa River. This site was unique in that channel catfish was the second most common
species, Evidence was presented of a large migrating channel catfish population that
occupied this section of the Yampa River. Channel catfish recruitment was apparently
improved by the 2002 flow conditions, Density and biomass of blue head sucker was much
reduced in 2003 compared to 2000. There was a noticeable shift in size structure in 2003,
with a much reduced incidence of the adult flannelmouth sucker and bluehead sucker larger
than 35 cm compared to 2000,

Four years of composition, density, biomass and size-structure data were given on the
Colorado River, with the baseline data from 1999,2000 and 2001. Only subtle changes were
found in the native fish population in 2003, which indicated that one year of low flows was
not highly problematic for native fish in the IS-Mile Reach.

One year of composition, relative abundance and size data was given for three sites
on the Gunnison River. The Gunnison River had the highest relative base flow conditions of
the study rivers and also apparently had the largest population of the native bluehead sucker,
flannelmouth sucker and roundtail chub, Surveys by the Fish and Wildlife Service also
found higher catch rates of native species on the Gunnison River than in the Colorado River.
It was concluded that the Gunnison River likely had better habitat availability for these native
species than the larger Colorado and Yampa Rivers, It was also concluded that reduced peak
flows in the Gunnison River were not problematic for bluehead sucker, flannelmouth sucker
and roundtail chub, In spite of reduced peak flows Burdick (1995) found a small population
of Colorado pikeminnow had reproduced successfully in recent years.

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