8138

• UCREFRP Catalog Number: 8138
• Author: Utah Division of Wildlife Resources, Arizona Game and Fish Department and The National Park Service.
• Title: Glen Canyon National Recreation Area Utah/Arizona\
• USFW Year: 1996.
• Copyright Material: NO

` inflow may be found near Neskahi Canyon and at that level habitat critical to
the survival of endangered fish may extend to Neskahi Canyon.
While nonnative fish dominate the biomass of fish in the inflow areas, recent
investigations have revealed the presence of Colorado squawfish and razorback
suckers in lake inflow reaches. Young-of-year squawfish frequent the Colorado
River inflow in most years, however, they are more numerous in the spring and
appear to successfully overwinter or continually migrate downstream through
the winter. Pre-runoff surveys conducted by BIO/WEST, Inc. in April 1993,
found 101 squawfish in the Colorado River inflow reach of Glen Canyon NRA, but
in the fall post runoff survey in August, only 3 squawfish were encountered.
Fry, spawned in the river in mid-summer, drift with the current until they
settle out in backwaters or the inflow area. Less squawfish at the inflow in
the fall suggest young fish either moved back upstream when the current
lessened or were heavily cropped by predation in the inflow area. In the
Colorado River inflow, it appears that squawfish may be able to overwinter,
but no overwinter survival has yet been documented in the San Juan Arm of Lake
Powell. In 1994 UDWR found two squawfish that survived over winter below
Grand Gulch.
A tagged adult squawfish captured in the San Juan inflow and released at point
of capture was recaptured 1 months later in the San Juan River near Bluff,
Utah. This has been the only documented case of squawfish movement between
Lake Powell and the San Juan River. Another documented case of squawfish
movement from Lake Powell to the Grand Junction area occurred in 1981-82 by
USFWS. The number of squawfish frequenting the Colorado inflow greatly
exceeds those found at the San Juan inflow.
When the lake first filled, sediment was deposited in the braided channel of
the San Juan river near Paiute Farms Mash. As lake elevation receded from
full pool, the San Juan River cut a new course through the sediment and over a
rock ledge which became a waterfall of about 25 feet in height near Paiute
Farms. The waterfall created a temporary barrier to fish passage upstream
from Lake Powell into the San Juan River in the late 1980's and early 1990's.
While the waterfall hindered upstream invasion of nonnative fish into the
flowing San Juan River (a benefit to natives in the river), it also precluded
upstream migration of YOY, or adult native fish (a liability to recruitment of
natives). The waterfall also acted as a dam by reducing the river gradient.
The waterfall was inundated by the filling lake in 1995 and the migration
barrier was eliminated. Recent surveys suggest that there may have been an
influx of nonnatives moving above the recently covered waterfall. The
waterfall may reappear as lake levels decline in the future.
The number of razorback suckers found in the Glen Canyon NRA in recent years
has declined dramatically. A few adult razorback suckers were removed from
the inflow reach of the San Juan River in the late 1980's and early 1990's.
These fish are being held in hatcheries as broodstock. Recent surveys for
adult razorback suckers have been unsuccessful, with the exception of one
experimentally stocked, radio-tagged razorback sucker that was captured by
NBS/BOR/NPS point survey efforts (March '95) in the San Juan inflow. Numbers
of razorback suckers in Lake Powell, the inflows, and the San Juan River
appear to be at all time lows.
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