9413

• UCREFRP Catalog Number: 9413
• Author: Osmundson, D. B.
• Title: Flow Regimes for Restoration and Maintenance of Sufficient Habitat to Recover Endangered Razorback Sucker and Colorado Pikeminnow in the Upper Colorado River.
• USFW Year: 2001.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

May or June only). Selection of runs changed toward the end of spring when use of higher
velocity sites increased: slow runs declined in use from 32% (April) to 27% (May) to 13%
(June); during the same period, fast runs increased in use from 0-3% to 19%.
Summer
During summer, flows decline in magnitude from relatively high levels in July to the
yearly low in September and water temperatures are at an annual high during July and
August. Use of fast runs peaked in July at 26% and then tapered off to 7% in September.
Conversely, use of slow runs increased during this period: after reaching an annual low in
late spring (13%) use steadily increased through summer (26-55%) and peaked during the
transitional month of October (61%). Together the two run types accounted for 49-52% of
habitats selected during summer. Backwaters were little used during this time (3-7%) and
flooded gravel pits were largely unavailable. Shorelines and rapids each accounted for only
04% use. Annual use of riffles was highest during the summer months but use was
relatively low compared to other habitat types (3-10%). Colorado pikeminnow use of
eddies also reached a yearly high during summer (9-16%). Pools were also used (13-16%),
but as in spring, summer use of pools was low compared to the remainder of the year.
Eddies, pools and backwaters were the preferred habitat types of adult pikeminnow in the
15-mile reach during summers with moderate base flows (Fig. 2). During summers of low
flow, slow runs and fast runs were preferred.
Transitional periods
Flows and temperatures are low during October and March and changes in fish
habitat use indicated these were transitional months that marked the beginning and end of
winter. Water temperature during October is somewhat higher than during March. Pools
and slow runs were primarily selected during these months: pool use accounted for 32% in
March and 26% in October; slow runs, 43% in March and 61% in October. Large
backwaters were used 14% of the time in March and 9% in October. Other habitat types
were used little or not at all: eddies were used 4-7%; fast runs 04%; riffles, rapids,
shorelines were not used and flooded gravel pits were unavailable.
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