7848

• UCREFRP Catalog Number: 7848
• Author: Burdick, B. D.
• Title: Minimum Flow Recommendation For Passage Of Colorado Squawfish And Razorback Sucker In The 2.3-Mile Reach Of The Lower Gunnison River
• USFW Year: 1997.
• USFW - Doc Type: Redlands Diversion Dam To The Colorado River Confluence.
• Copyright Material: NO

in 1993 by FWS that collected 21 species of fishes: 7 native, 14 nonnative, and
three catostomid hybrids (Burdick 1995). The 2.3-mile reach corresponds to Reach
1 of that study and former FWS studies (Valdez et al . 1982b) and extends from the
Redlands Diversion Dam downstream to the confluence with the Colorado River.
Former capture and radiotelemetry data indicate adult Colorado squawfish utilize
the Lower Gunnison River and plunge pool from April to September.
Larval Colorado squawfish have been collected up- and downstream of the
Redlands Diversion Dam. One larval Colorado squawfish was collected immediately
downstream of the Redlands Diversion Dam in 1986 (28 August; Osmundson and
Kaeding 1989). Two other larval Colorado squawfish were collected in this reach
in 1992 (2 and 10 July: Anderson 1994). Six larval Colorado squawfish were
collected in 1995 and eight in 1996 (Personal communication, Richard Anderson).
In 1995, five were captured upstream of Redlands, two at RM 5.2 (16 August) and
three at RM 29.3 (16, 17, and 18 August). The one downstream specimen was
collected at RM 2.6. In 1996, one was captured at RM 29.3, four at RM 5.2, and
three at RM 2.6. The capture of larval fish in 1995 and 1996 indicates spawning
of Colorado squawfish is occurring in the Gunnison River upstream of Redlands
Diversion Dam, possibly as far as Bridgeport (RM 29.3). Of the large-sized
fishes, four other native and nine nonnative fishes occupy the reach with
Colorado squawfish. The most common of these large fish include the native
bluehead sucker, flannelmouth sucker, and roundtail chub.
Compared to adjacent areas in the 15- and 18-mile reaches of the Upper
Colorado River that have been generally classified as a heterogenous habitat
(Osmundson et al. 1995), the 2.3-mile reach could be classified as a homogeneous
habitat, comprised primarily of long, laminar runs. The average gradient is 7.0
ft/mi compared to 9.0 ft/mi in the 15-mile reach. The reach has only two side
channels, one at RM 2.9, the other at RM 1.3. The plunge pool and site of the
former "Black Bridge" are the only areas where deep pools are found, even during
periods when the reach has been dewatered. Slow run and riffle habitats become
noticeable only during flows less than 600 cfs. Stream braiding is non-existent.
The Clymer's ditch returns a small irrigation flow to the Gunnison at RM 1.3.
Tamarisk and Russian olive are the predominant vegetation type whereas willow
occurs infrequently.
METHODOLOGY
Biological
Electrofishing
El ectrof i shi ng was used to collect sub - adult and adult fish. Sampling was
conducted from an outboard-powered, aluminum electrofishing jon boat, equipped
with a 5-kilowatt generator and a Coffelt VVP-15 voltage pulsator to adjust the
voltage and amperage transmitted to the water. The electrofishing boat used two
spherical anodes (about 9-inch diameter) suspended from fiberglass booms in front
and two 7-ft cathodes (0.25-inch diameter twisted cable) suspended from each side
of the boat. The boat was also used as a cathode in conjunction with the
droppers. Both the anode and cathode were stainless steel. Investigators used
direct current and tried not to exceed 300 volts or 12 amps to minimize injury