8170

• UCREFRP Catalog Number: 8170
• Author: Trammell, M. A., K. D. Christopherson, C. L. Rakowski, J. C. Schmidt, K. S. Day, C. Crosby and T. E. Chart.
• Title: Flaming Gorge Studies
• USFW Year: 1999.
• USFW - Doc Type: Assessment of Colorado Pikeminnow Nursery Habitat in the Green River.
• Copyright Material: NO

1

- At Oura backwaters used b Colorado ike '
y, y p minnow had mean length 1.8 times that of
unused backwaters. Likewise, mean width was 1.7 times greater and mean volume 2.2
times greater.

- Secondary (scour) channel backwaters had mean surface azea, mean depth, cover, and
aspect values closest to those of the "avera
e" backwater
d b
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use
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pikeminnow.
- Secondary (scour) channel habitats made up the majority of available habitat and were
chazacterized by lazge size, depth, and stability. These tend to be perennial habitats
that change primarily as a result of river levels, but aze available every yeaz. Because of
their wide mouths and positioning in the river system, they accumulate more fine
substrate and may also more readily capture drifting larvae and food items. They
'~, generally do not have the extreme temperature fluctuation seen in smaller backwaters.
- Temperature appeazed to play a role in habitat selection by Colorado pikeminnow in
this study during spring and summer. In summer samples, backwaters containing
Colorado pikeminnow were significantly warmer than others, but the difference was
only 1.0°C. Similar results were seen in spring backwater samples, but significance
was atp<0.10. Backwaters used in the spring were actually closer (+2°C) to main
channel temperature than unused backwaters (+3.1 °C).
- Turbidity has also been noted as a distinguishing characteristic for Colorado
pikeminnow use. Backwaters with Colorado pikeminnow were more likely to have
higher turbidity ratings than unused backwaters. Colorado pikeminnow were found
more often in backwaters opening in a downstream direction.
- The inability to develop an easily applicable model for discriminating between suitable
and unsuitable backwaters is problematic, but not entirely unexpected. Extreme
variability in backwater formation and availability, river conditions, and Colorado
pikeminnow cohort strength between years precluded developing this simple model.
However, the models produced are promising for eliminating backwaters from
consideration.
-
At Mineral Bottom, nonnative cypruuds selected for secondary (scour) channel habitats.
Although they were present in almost all habitats, catch rates were higher in scour
channel habitats.
- At Ouray, fall catch rates of nonnative cyprinids were positively associated with high
spring flows. At Mineral Bottom, they were negatively associated.
- This study found a high degree of variability in the correlation of CPLTE for the various
fish species. Both native and nonnative fish had examples where positive and negative
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