9315

• UCREFRP Catalog Number: 9315
• Author: Harvey, M. D. and R. A. Mussetter.
• Title: Evaluation of the Required Frequency of Bar Forming Events and 2-Dimensional Hydrodynamic Modeling at Colorado Squawfish Spawning Sites in the Lower Yampa Canyon, Colorado.
• USFW Year: 1996.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

V.
Lower Yampa River (just upstream of the Yampa-Green River confluerice, Echo
Park, Dinosaur National Monument), Colorado, and lower Green River
(possibly near the town of Green River), Utah.
Study Methods/Approach:
Passive drift-net sampling is an effective and proven method for capturing
Colorado squawfish larvae. In properly conducted, results can provide a
reasonable estimate of annual reproductive output from spawning agrees
without over-sampling larvae.
Drift-net sampling in the Yampa and Green rivers, as part of FGFRI, was
started in 1990 and will be conducted again in 1991. In 1991, two drift-
net stations were established, i.e., lower Yampa River at Echo Park and
Green River just below the Split Mountain boat ramp. At each station,
three flow-metered plankton nets were set near the shore, daily at dawn
for 1-2 h, from end of June through early August. The objectives of this
sampling were to document timing and duration of spawning by Colorado
squawfish in the lower Yampa River, determine peaks in abundance of
transported Colorado squawfish larvae transported from the lower Yampa
River spawning area into nursery habitats in the Jensen-Ouray area;
nursery-habitat sampling conducted by Utah DWR (SDCR Task 2) in fall 1990
was intended to subsequently determine abundance of young Colorado
squawfish in backwater habitats. Results of the 1990 drift-net sampling
were provided in an annual progress report submitted to the U.S. Bureau of
Reclamation. After discussions with the cooperative FGFRI team in
December 1990, the drift-net sampling scheme used in 1990 was changed in
favor of the design proposed here (this new study design will be employed
in 1991).
Reproductive output will be measured by daily captures of drifting
Colorado squawfish larvae at two sites, one at mouth of the Yampa River
and one below Grey and Desolation canyons in the lower Green River. Both
of these sites are below known spawning grounds, and data from sampling at
these sites will provide estimates of relative abundance of Colorado
squawfish larvae being transported from spawning areas and into potential
nursery habitats.
Colorado squawfish in the Yampa River spawn on the descending limb of the
hydrograph, often associated with abrupt increases (flow spikes) in base
flow (Nesler et al. 1988; Tyus and Karp 1989). Sampling for Colorado
squawfish larvae will be initiated based on those data and stream-flow
conditions prior to sampling (probably start in mid-late June). Duration
of the sampling period will depend on number of larvae collected in late-
season samples, past data, and stream-flow conditions probably end early-
mid August).
Colorado squawfish larvae are most abundant in drift-net samples at dawn
and nearshore and midstream nets capture roughly equivalent numbers of
fish/unit volume of water sampled (Haynes et al. 1984; Nesler 1986). This
was supported by results of out nearshore sampling during summer 1990;
catch rates of three nearshore drift nets were similar (one-way ANOVA).
Results of the 1990 sampling showed that about 60% of drifting Colorado
'period on only four sampling days; we determined that daily sampling over
a 6-8-week period was necessary to detect and measure peaks in larval
abundance and bracket the period of larval transport.
At each station, three 4-m-long conical plankton nets (560 micron mesh)
will be set daily at dawn. Nets will be attached to rectangular steel
frames (0.15 mZ) and staked into the stream substrate adjacent to the shore
in water 0.5-1.0 m deep. A removable collection bucket for trapping
filtered material and fishes will be attached to the cod end of each net.
C3