9524

• UCREFRP Catalog Number: 9524
• Author: Kitcheyan, C. D. and e. al.
• Title: Evaluation of the Effects of Stage Fluctuations on Overwinter Survival and Movement of Young Colorado Pikeminnow in the Green River, Utah, 1999-2002.
• USFW Year: 2004.
• USFW - Doc Type: Denver.
• Copyright Material: NO

SYNTHESIS
This study was unable to show that fluctuating winter flows due to releases from Flaming Gorge
Dam to meet hydropower needs added additional stressors to overwintering young Colorado pikeminnow.
Several investigators have hypothesized that winter operations of Flaming Gorge Dam influence age-0
fish survival (Carlson and Muth 1989; U. S. Fish and Wildlife Service 1992; Valdez and Cowdell 1996;
Haines et al. 1999). A 24-hr hydropower release from Flaming Gorge Dam during this study fluctuated
about 600 to 800 cfs, producing stage changes at the Jensen gage <0.1 m (93 miles downstream of
Flaming Gorge) and about <0.01 m at the Ouray bridge. These stage changes had only minimal affect on
backwater habitats and were limited to the upper end of the nursery area. These flow fluctuations did not
alter the physical morphology of backwaters studied in the Ouray Backwater Complex. The formation of
ice jams, however, had a far greater affect on the backwater nursery habitats, increasing stage by 0.75-
1.50 m, resulting in the transformation of many backwater habitats into flow-through areas. The role of
fluctuating winter flows from Flaming Gorge Dam in the creation of ice jams is unclear. Valdez and
Cowdell (1999) speculated that fluctuating winter flows may dismantle ice cover which acts an insulator,
allow the creation of frazil, and may result in ice jams that increase river stage several meters and
inundate many backwaters. Hayse et al. (2000), however, found that fluctuating winter flows from
Flaming Gorge Dam did not dismantle ice cover thereby promoting formation of frazil ice and ice jams.
Whatever the cause, it is likely that ice jams form at several locations on the middle Green River nursery
area in most years (Valdez and Masslich 1989; Valdez and Cowdell 1999; Hayse et al. 2000).
As a result, stage changes due to ice jams and frazil ice formation may force young fish to
redistribute and seek alternate low-velocity channel-margin habitats (Muth et al. 2000). Young Colorado
pikeminnow prefer low velocity backwater habitats (Tyus and Haines 1991); when these habitats are
inundated, the fish abandon them and move to other low velocity habitats, sometimes to other backwaters
several miles away and sometimes to low-velocity micro-habitats within close proximity of the inundated
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