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

The Gunnison River had a very large native fish population in contrast to a very low
native fish population in the Yampa River. The two most obvious factors explaining this
difference were: I) high base flows with abundant habitat availability versus low base flows
that provide poor habitat availability and 2) no nonnative predators versus a high predator
population,

The Gunnison River had the highest composition and population size of roundtail
chub and was also the river without a channel catfish population, It was observed that the
site (Lily Park) with a large channel catfish population had no roundtail chub and the sites in
the] 5-Mile Reach that had an intermediate channel catfish population had an intermediate
round tail chub population, This trend suggested a cause and effect relationship.

Peak flows on the Gunnison River have been severely downsized. Burdick (1995)
identified an apparent Colorado pikeminnow spawning location in the Gunnison River in
spite of a poor spring hydrograph for this river. Anderson (1997) found similar numbers of
larval Colorado pikeminnow in the Gunnison River and the 15-Mile Reach, The persistent
population of Colorado pikeminnow upstream of the Redland Diversion dam may have been
related to the absence of green sunfish and bass in the community. The presence of predators
in the Colorado River likely explained the poor survival oflarval pikeminnow (Bestgen
1997),

DOLORES RIVER

Anderson (2002) reported fish sampling data for the Dolores River in the Big
Gypsum Valley, about 35 miles upstream from Bedrock, In 2000, 54% of the total catch
(1,078) was less than 15 cm in length compared to 77% (2,795) in 2001. For fish <15 cm
87% were native species in 2000 dropping to 58% in 2001. Roundtail chub and speckled
dace were the most common native fish reported on the Dolores River by Anderson (2002),
Valdez (1992) reported native fish composition collected by electrofishing was 86% near
Bedrock and 77% near Slickrock from samples made in 1990 and 1991,

The CDOW collected data on the Dolores River about 25 miles upstream of the
Anderson site, Biologist Mike Japhet collected this data from a 1,000 ft reach of the river
below the Dove Creek power plant. From 1986 to 1991, the percent of fish less than 15 cm
was 81 %,91 %,75%,86% and 88%. From 1992 to 2003 nearly all fish collected were less
than 15 cm (97% to 100%), Native fish ranged from 97% to 100% of the catch (excluding
stocked brown and rainbow trout) for fish < 15cm from 1986 to 2000. In 2002 and 2003,
native fish composition dropped to 79% and 76% respectively. These data suggested
nonnative species composition increased in recent years and fish> 15 cm were very rare,

The Dolores River had a high composition of native fish, but very low biomass due to
the lack of large fish in the population (Anderson 2002). Small body-sized speckled dace
and mottled sculpin were common at the Dove Creek site (M, Japhet, personal comm.),
Roundtail chub were also very common, but were small, rarely exceeding 15 em, Most of
the flannelmouth sucker and bluehead sucker were also small (< 20 cm), Small.sized fish
appeared to have been the trend in the Dolores River at Dove Creek since sampling started in

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