9319

• UCREFRP Catalog Number: 9319
• Author: Mueller, G., M. Horn, Q. Bradwisch and L. Boobar.
• Title: Examination of Native Recruitment and Description of the Fish Communities Found in the San Jan and Colorado River Interface Zones of Lake Powell, Utah.
• USFW Year: 2001.
• USFW - Doc Type: 01-159,
• Copyright Material: NO

scoured off the bar during August as declining flows resulted in increased slope
and velocity in the spawning channel.
Bed material analysis of sand deposition at the spawning channel
indicates that sand between 0.5 - 1.0 mm in diameter predominates. Sediment
transport samples collected in 1996 indicate that this size material moves mostly
as bedload as flows approach 425 m's-'. Scour chain analysis in an overflow
channel immediately above the spawning area indicates that sand sized material
is supplied to the spawning channel on the rising limb as flows exceed
325 m's'.
From an evolutionary perspective, based on large percentage of ripe
adult fish using the site, age structure of the adult population, and recruitment
success patterns since closure of Flaming Gorge, it is not logical that the
primary spawning bar at river kilometer 500 would be a consistently poor
producer of larvae during high flow years. Historical recruitment success
appears tied to years when high flow conditions provided river connectivity to
floodplain habitat. Physical process and biological response data collected
during this study showed that spawning conditions remain suitable and numbers
of razorback larvae are higher at reference collection sites below the spawning
bar when Green River discharges at Jensen remain below present effective
discharge of 325 m's-'. Sedimentation begins to impact the site as flows exceed
325 m3s'' and numbers of razorback larvae caught at reference collection sites
are considerable lower than in years when flows do not exceed this level.
Razorback adults must spawn and resultant larvae hatch and emerge from cobble
substrates prior to deposition of sand which can bury and/or suffocate the larvae.
It is hypothesized that reductions in peak discharges on the Green River
below Flaming Gorge Dam have resulted in sediment being stored at low
elevations in the channel bed and river margins due to a lower range of peak
flows. This has led to conditions where available sediment is now transported at
a narrower range of lower peak flow levels. Effective discharge levels on the
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