8233

• UCREFRP Catalog Number: 8233
• Author: Chart, T. E., D. P. Svendson and L. Lentsch.
• Title: Investigation of Potential Razorback Sucker ‎(Xyrauchen texanus)‎ and Colorado Pikeminnow ‎(Ptychocheilus lucius
• USFW Year: 1999.
• USFW - Doc Type: Spawning in the Lower Green River, 1994 and 1995.
• Copyright Material: NO

Colorado pikeminnow
Colorado pikeminnow is the largest North American cyprinid and is endemic to the
UCRB. The most stable population of Colorado pikeminnow persists in the middle Green River
and its tributaries, the Yampa and White rivers. Known Green River spawning sites are found in
Yampa Canyon and in Desolation Canyon. Tyus et al. (1987) suspected a Colorado pikeminnow
spawning site in the lower Green River and Valdez (1990) collected protolarvae downstream of
Millard Canyon (RK 53.9, RM 33.5). Based on comparisons of habitat characterizations with
other Colorado pikeminnow spawning sites and the Valdez collection of larvae, the debris fan at
the mouth of Millazd Canyon was selected as the primary azea of interest for Colorado
pikeminnow observations.
OBJECTIVES
The objectives of this study were to: 1) determine the presence / absence of "possible"
razorback suckers in past collections of Age 0 fish from the lower Green River (coordinate with
LFL), 2) determine presence /absence of spawning razorback sucker in the lower Green River
(RK 192 - 153), 3) determine presence /absence of larval and Age 0 razorback suckers from RK
192 - 0.0, 4) examine historic collections /data from the lower Green River to determine if a
downward shift in size distribution is evident in fish from the lower stretches; suggesting local
spawning, 5) determine if Colorado pikeminnow spawn neaz the mouth of Millard Canyon, 6)
determine presence /absence of larval pikeminnow in the lower 50 km of the Green River.
STUDY AREA
The study area for these investigations was the lower Green River from RK 209.3-40.7
(RM 130.0-25.3) (Figure 1). Sampling occurred at intervals throughout this 168 km reach but
species and lifestage specific sampling was conducted in azeas of particulaz interest. Specific
areas of interest included: razorback sucker adults-habitats from Swayze Rapid (RK 209.3, RM
130.0) to Ruby Ranch (RK 156.2, RM 97.0) (two reaches); Colorado pikeminnow adults-debris
fan at the mouth of Millazd Canyon (RK 53.9, RM 33.5) downstream to RK 40.7 (RM 25.3);
razorback sucker larvae-habitats including and directly below the Green-San Rafael river
confluence (RK 156.2-151.3); and Colorado pikeminnow larvae-habitats below the suspected
spawning area at the mouth of Millard Canyon downstream to RK 40.7.
The two years sampled (1994 and 1995), comprised two extremely different flow regimes
(Figure 2.). In 1994, Green River flow, as measured by the U.S. Geological Survey (iJSGS)
gage #09315000 (Green River at Green River, Utah) peaked at 331.34 m3/sec (11,700 cfs) on 22
May. Comparatively, the same gage in 1995 recorded a peak of 829.78 m3/s (29,300 cfs) on 18
June. The impact of these different hydrologic regimes will be discussed later.
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