8158

• UCREFRP Catalog Number: 8158
• Author: Osmundson, D. B.
• Title: Longitudinal Variation in Fish Community Structure and Water Temperature in the Upper Colorado River; Final Report.
• USFW Year: 1999.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

The bulk of fish caught in upstream strata consisted of native species, primarily bluehead and
flannelmouth sucker. Catch rates of bluehead sucker were generally higher in upstream strata
than in downstream strata. The exception to this was in Stratum 10 where the catch rate was
not significantly different from catch rates in downstream strata 2-6 nor from upstream
Stratum 7 (Appendix Table 4). Catch rates of bluehead suckers were significantly lower in
Stratum 10 than in other upstream strata (strata 8-9 and 11-12).
Catch rates of flannelmouth sucker were generally higher in upstream strata than in
downstream strata and catch rates among upstream strata 7, 8, 9, 11 and 12 were similar
(Figure 2). Again, the Stratum 10 catch rate was not significantly different from catch rates in
downstream strata 2-6 (Appendix Table 5). Roundtail chub catch rates in all upstream strata
were significantly higher than in all downstream strata and were similar among downstream
strata 1-6 and were similar among upstream strata 7-12 (Appendix Table 6). The catch rate
of speckled dace Rhinichthys osculus was significantly higher in Stratum 9 than in all other
strata (Appendix Table 7). For common carp (Cyprinus carpio), no longitudinal pattern was
evident, though catch rates in upstream strata 10 and 11 were some of the lowest and the
catch rate in Stratum 2 was significantly higher than in most other strata (Appendix Table 8).
The most upstream Colorado River stratum (Stratum 11) had significantly higher catch rates
of white suckers Catostomus commersoni (and hybrids with native suckers) and salmonids
(primarily mountain whitefish Prosopium williamsoni) than any other stratum (Appendix
Tables 9 and 10). In downstream strata 1-6, nonnative common carp and channel catfish were
a larger proportion of the total catch than in upstream strata; nevertheless, more than half of
the catch in strata 2-6 consisted of native suckers.
Prey-size fish --Catch rates of fishes that might serve as forage for Colorado pikeminnow
(soft-rayed fish, 100-300 mm TL) were generally highest in strata upstream of Westwater
Canyon (Figure 3). Very few such fish were found in Stratum 1. Strata 7, 8, 9, 11 and 12
had statistically similar catch rates and these catch rates were all significantly higher than those
in downstream strata 1-6. The Stratum 10 catch rate was significantly higher than catch rates
in strata 1 and 2 and was significantly lower than the Stratum 12 catch rate; otherwise, the
catch rate there was not significantly different from those in strata 3-11 (Appendix Table 3).
In strata 2-6, the bulk of fish vulnerable to Colorado pikeminnow predation were bluehead
suckers. In strata 7-9, bluehead and flannelmouth suckers made up nearly equal proportions
of the catch and together made up most of the forage-sized fish. Catch rates of forage-size
flannelmouth sucker were significantly higher in Strata 7-9 than in downstream strata 1-6
(Appendix Table 5). Also, the catch rate of forage-size bluehead sucker in the Gunnison
River stratum was significantly higher than in any Colorado River stratum (Appendix Table 4).
Roundtail chub and white sucker (and associated hybrids) were the only other species with
relatively abundant numbers of forage-size individuals. Although catch rates of bluehead and
flannelmouth sucker (100-300 mm TL) apparently decreased upstream of Stratum 9,
abundance of young roundtail chub and salmonids (primarily mountain whitefish) increased.
The abundance of forage-size salmonids in Stratum 11 was significantly higher than in any
other stratum (Appendix Table 10).
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