8178

• UCREFRP Catalog Number: 8178
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 1999.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

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Table 1. Sevens species composition (fish over 150 mm) for total catch and
estimated numbers in the Representative Reach (RR) and the Surveyed
Site (SS), September 1998.

SEVENS REPRESENTATIVE REPRESENTATIVE SURVEYED
REACH REACH SITE
Species N % EST. % EST. %
Total fish 2219 6117 862
Flannehnouth Sucker 964 43.4% 2257 36.9% 241 28.0%
Bluehead Sucker 484 21.8% 1650 27.0% 121 14.0%
White Sucker* 377 17.0% 1016 16.6% 244 28.3%
(WSW}{)
Roundtail Chub 135 6.1% 409 6.7% 81 9.4%
Channel Catfish 133 6.0% 403 6.6% 75 8.7%
Carp 69 3.1% 209 3.4% 57 6.6%
Northern Pike 31 1.4% 94 1.5% 18 2.1%
Smallmouth Bass 23 1.0% 70 1.1% 21 2.4%
Crappie 7 0.3% ne. ne.
Colorado Pikeminnow* 3 0.1% 9 0.1% 3 0.3%
Native species 1586 71.5% 4325.203 70.7% 445.9903 51. 7%
Nonnative species 640 28.8% 1791.797 29.3% 416.0097 48.3%

The percent of native fish in the catch at Sevens was 71% (Table 1) and 14% at
Duffy (Table 2). The biggest difference between the two areas was flannel mouth
suckers, which were 43% of the catch at Sevens but 6% at Duffy. Bluehead sucker and
roundtail chub were 22% and 6%, respectively at Sevens compared to 4% and 3%,
respectively at Duffy. Together small mouth bass and northern pike Esox lucius
comprised 2% of the fish catch at Sevens compared to 12% at Duffy. Channel catfish
Ictalurus punctatus composition was higher at Sevens, while Colorado pikeminnow
Ptychocheilus lucius were more abundant at Duffy.

Results of electrofishing surveys by the Colorado River Recovery Program
(ISMP) indicate the percent composition of native fish decreases in an upstream
direction from Lily Park to Duffy Tunnel (Figure Al.l). ISMP collections 10 miles
downstream of Sevens at Lily Park (RM 52) had native fish at 91% of the total catch.
Flannelmouth sucker was 68% of the catch at Lily Park. Flannelmouth sucker
composition decreased in: an upstream direction and was 43% at Sevens (RM 62), 18%
at Maybell (RM 76), 8% at Juniper (RM 99) and just 4% at Morgan Gulch (RM 104)
and Duffy Tunnel (RM 110). White sucker and white sucker hybrids increased in an
upstream direction and the ISMP collections near Juniper (RM 99) had native fish at
18% (Figure A1.2). Nonnative predators (smallmouth bass and northern pike) and
Colorado pikeminnow tended to increase in an upstream direction (Figure A1.3).