6032

• UCREFRP Catalog Number: 6032
• Author: Maddux, H., et al.
• Title: Effects of Varied Flow Regimes on Aquatic Resources of Glen and Grand Canyons
• USFW Year: 1987.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

,:. effects of fluctuating flows on Cladophora life history; 4)
determine the effects of fluctuating flows on phytoplankton and
zooplankton life stages and the utilization and importance of
these plankton to the fish species at various life stages
throughout the study area; and 5) determine the importance of
natural reproduction versus artificial propagation to the
maintenance of the trout fishery in the Glen Canyon tailwater.
In addition to these objectives, we were to include, an analysis
of potential alternative operating criteria consistent with
Colorado River Storage Project (CRSP) requirements and to propose
feasible alternatives.
The first objective was to collect baseline data on fish
species composition and distribution in the Colorado River. This
information allowed the more important second objective of
comparing use of mainchannel and tributaries for spawning and
nursery areas for larval fishes and rearing of older fish.
Objective three was addressed through a combination of field and
laboratory studies by researchers at Northern Arizona
University. Because larval life stages of fishes may be
dependent on zooplankton, objective four was included. A
combination of plankton samples and larval fish gut analysis was
incorporated to address this objective., The fifth objective was
to establish whether rainbow trout in the Glen Canyon tailwater
were naturally reproducing and, if so, how much they contributed
to the creel. Other aspects of the ecosystem not covered in
these objectives but considered important were also addressed.
The five discharge scenarios are based on the minimum
release (8..3 million acre feet [maf]) established by law that
must be released annually through Glen Canyon Dam. A release
pattern based on 8.3 maf could have almost any combination of
steady and fluctuating flows. A major factor that affected
collection and analysis of data was the amount of runoff during
the study period. Annual releases from the dam ranged from 16.6-
21.1 maf during our study. Because of these high releases BOR
was not able to provide the various flow patterns necessary to
address all the questions raised in the study objectives. Most
data collection occurred during periods of high steady
releases. Only brief periods of fluctuations were provided
during the study, and these generally came during autumn and
winter.
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