7752

• UCREFRP Catalog Number: 7752
• Author: Stanford, J. A.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin
• USFW Year: 1993.
• USFW - Doc Type: Review and Synthesis of Ecological Information, Issues, Methods and Rationale.
• Copyright Material: NO

unregulated snow-melt river in Montana, were consistently less than 5% per day during the
baseflow period.
Repeated flushing of the varial zone prevents establishment of food webs and resting areas
for small fish that are required to support riverine fisheries. Weisberg et al. (1990) 4~monstrated
that standing crops of zoobenthos increased 100 fold in one year in a regulated river after
eliminating peaking operations at the dam and thereby reducing the devastating ecological effects of
unnatural, short-term flushing of the varial zone. Repeated flushing also removes plant growth
nutrients and alters the natural thennal insolation of shallow backwaters that are especially
important for bioproduction of low velocity food webs in general, and for growth of squawfish and
razorback sucker specifically.
In spite of the laudable reregulation effort by operators of Flaming Gorge Dam to stay
within flow windows (Figure 14) determined to maximize areas of backwater habitats in the alluvial
nursery areas of the Green River during summer and fall, 1992, peaking operations still caused
considerable diel fluctuation of river stage (e.g., Figures 12-14). I infer that backwaters thought to
be protected by these flow windows were in fact flushed or, at least, dramatically fluctuated
repeatedly during the late summer, 1992. Data presented by Graboski and Heibert (1989) suggest
that the food webs in the backwater environments of the Green River are not very productive. As
noted above, these backwaters should contain rooted aquatic plants and a biodiverse, productive
invertebrate and fish food web. I realize that the fluctuations shown in Figures 12-14 are
considerably reduced from operations in the past. Nonetheless, development of stable, productive
food webs in the backwaters probably have not occurred as a consequence of reregulation of the
Flaming Gorge releases. Moreover, they will not likely ever be very productive, unless flow
fluctuations can be eliminated. Empirical information with which to fmnly judge the productivity of
backwater food webs as influenced by regulated baseflow regimes throughout the Upper Colorado
River Basin is sorely needed and should be approached in the dynamic time and space context
described above.

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