8025

• UCREFRP Catalog Number: 8025
• Author: Valdez, R., et al.
• Title: Colorado River Fishery Project, Tributary Report ‎(Gunnison and Dolores River)‎ Final Report.
• USFW Year: 1982.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

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The total CPE was 75.0 fish/10 hr using hour gear (Table 7). This
seemingly high value is deceptive, because it is based on a small amount
of effort (1.2 hr). No fishes were collected 1n stratum W using
area-based gear.

Flows in the Dolores River were more dramatically reduced by
withdrawals than those in the Gunnison River. In 1981 (except for the
runoff period--April to mid-July) the Dolores River usually flowed at
less than 500 cfs (Figure 4). CPE values viewed over months in which
sampling occurred illustrated some significant changes in fish abundance
with corresponding changes in flow (Table 8 and 9). A similar movement
of juvenile and adult native and endemic fishes was seen from May to
August (Figure 7). Bluehead sucker, flannelmouth sucker and roundtail
chub increased in abundance from early May to mid-May, corresponding with
runoff. TIlese species then gradually decreased in abundance from mid-May
to August, when few natives or endemics were found in the Dolores River
at low flow. TIle Dolores River had little surface water flow after late
August 1981, and a few remaining pools harbored large numbers of
non-native fishes and few natives.

Species Composition by Habitat

Gunnison River

Backwaters. Backwaters, although few in number, appeared to be an
important habitat in the Gunnison River. TIlirteen species (nine
non-native, two endemic and two native) were collected from Gunnison
River backwaters. Backwaters were more attractive for non-native species
than any of the other habitat types. Over half (51.3%) of the total
catch in backwaters was composed of non-native fishes. Sand shiner
(21.2%), fathead minnow (20.8%) and bluehead sucker (15.3%) were the most
abundant species in backwaters.

CPE values (area and hour-based gears) for each species in each
habitat are shown in Tables 10 and 11. CPE comparisons suggest that
backwaters were less important for larger fishes, as indicated by
_relatively small catch values for hour-based gears. TIle total hour CPE
was 3.24 fish/lO hr, less than all other habitats sampled. Backwaters
were apparently more important areas for smaller fishes, as total area
CPE was 15.24 fish/10m2. Only side channels and eddies had higher
total area CPE values.

Eddies. Nine species (five non-native, two endemic, and two native)
were found in eddies in the Gunnison River. Endemics comprised 87.1% of
the total catch. Roundtail chub were the most abundant species caught in
eddies (76.7%), followed by flannelmouth sucker (10.4%) and bluehead
sucker (9.0%). Fathead minnow and sand shiner were the most common
non-native species, accounting for 2.5% and 1.37., respectively.

Based on relatively high CPE values for area-based gears, it appears
that eddies were important for small fishes in the Gunnison River. Total
area CPE was 30.42 fish/10m2, highest for all habitat types sampled