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

these stocked trout.
sampled fish in Reach
collected downriver.
Lee's Ferry area for a
dyed,. Rainbow trout
individuals checked in
FISH FOOD RESOURCES
Dye marked trout represent 61% of the
10, but very few marked individuals were
Natural reproduction is occurring in the
11 sampled fish 100 mm or smaller were not
that were not dyed constituted 27.5% of
the creel.
Food resource utilization of fishes was examined by analysis
of gut contents. Gut analyses were accomplished for fry of three
species; rainbow trout, bluehead sucker, and flannelmouth
sucker. Only adult rainbow trout guts were examined.
Immature chironomids were numerically predominant in fry
guts of all three species. Zooplankton, primarily copepods and
cladocerans, was of second highest proportion in flannelmouth
sucker and mainstream rainbow trout fry, but other immature
insects held this position in bluehead sucker fry. Proportion of
zooplankton declined dramatically in rainbow trout fry collected
below Reach 10.
Adult rainbow trout guts had high volumetric proportions of
the filamentous green alga, Cladophora glomerata, immature
insects (mainly chironomids and simuliids), or the amphipod,
Gammarus lacustris, depending on the stream reach considered.
Proportions of these major food groups also varied on a seasonal
basis. Gammarus proportion increased dramatically during a
period when dam releases were dropped deliberately. This
suggests that the amphipod's susceptibility to trout predation
can be affected by operations of Glen Canyon Dam.
AGE AND GROWTH
Length frequency distributions were used to estimate growth
of fish because it was not possible to age fish by conventional
scale and otolith methods. Growth rate of rainbow trout was
highest in upper reaches of the Colorado River and decreased
below the confluence of the Little Colorado River. Condition
factors for rainbow trout also decreased with distance downstream
from Glen Canyon Dam.
First year growth of humpback chub was estimated to be 70 mm
based on length frequencies. Growth of adults (>250 mm) was
estimated to be approximately 10 mm/yr. First year growth of
bluehead and flannelmouth sucker was estimated to be
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