7056

• UCREFRP Catalog Number: 7056
• Author: Archer, D. L. and H. M. Tyus.
• Title: Yampa River Colorado Squawfish Spawning Study.
• USFW Year: 1984.
• USFW - Doc Type: Salt Lake City, Utah.
• Copyright Material: NO

Our data and those of Wick, et al. (1983), indicate that Colorado
squawfish spawning activity in the Yampa River is keyed into a reach
extending from Warm Springs rapid RK 7 (RM 4.1), upstream approximately
to the vicinity of Harding Hole RK 32 (RM 20). It further appears,
through repeated captures of ripe fish, that spawning activity (i.e.,
the actual deposition and fertilization of eggs) is concentrated in a
unique reach between RK 24 (RM 15) and 30 (18.8). This portion of the
Yampa River is dramatically different from any other throughout its
course. It meanders, becomes braided with islands, cobble and sand bars
and slows considerably. Large deep pools intermingled with riffles and
runs, and imbricated cobble substrate predominate in this reach.

Based on the time of year in 1981, 1982 and 1983, whenColorado
squawfish migrated into and out of the spawning reach (Figures 2 and 3)
(Wick et al. 1983), the time frame for spawning activity on the Yampa
River varies from year to year. Whether this time is a function of
photoperiod, flow, water temperature, sexual maturation or a combination
of one or more factors, is unknown. But, to maintain' the cobble substrate
in optimal condition for spawning, it appears that a minimum flow is
needed between the peak flow and the onset of spawning in July and
August. This minimum flow would remove sand from the cobble substrate
prior to spawning. In this respect, while it has been well documented
that Colorado squawfish enter the lower Yampa during their spawning
period, little was known about hydraulic parameters utilized by the fish
during spawning activities.

Through application of the Incremental Stream Flow Methodology
(ISFM), developed by the Instream Flow and Aquatic Systems Group, (FWS),
habitat availability for Colorado squawfish spawning in the lower Yampa
River at a variety of flow levels was quantified in 1983. CRFP fish
data was combined with physical habitat data for use with the ISFM (i.e.
depth, velocity and substrate information). The Ecological Services
(ES) Division of FWS (Rose 1984) carried out the ISFM procedures on the
Yampa River during the 1983 field season at two sites.

The "spawning bar" site at RK 26.4 (RM 16.5) was selected because
reproductive behavior had been observed there in the previous two years
(Figure 10). The second, or "replicate site" at RK 29.6 (RM 18.5) was
selected because sexually mature fish had been collected and radio-
tagged fish monitored there in 1981, it exhibited similar characteristics
to the site at RK 26.4, and was within the unique reach between RK 24
and 30 (Figure 11).

Physical data collected at the two sites, and Colorado squawfish
spawning utilization curves (Rose 1984) developed from CRFP observation
data were combined with physical habitat simulation (PHABSIM) computer
models to determine habitat availability at the two sites for two
phases- of spawning activity (staging/resting and deposition/fertilization).
Habitat utilization curves for spawning Colorado squawfish, were developed
for both phases by partitioning the physical data accordingly:

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