7145

• UCREFRP Catalog Number: 7145
• Author: Inslee, T. D.
• Title: Spawning of Razorback Suckers
• USFW Year: 1981.
• Copyright Material: NO

to dislodge tamarisk seedlings that had become established during the
previous two low-water years or flush large backwaters of accumulated
sediments (Osmundson, personal observation). Establishment of tamarisk is
viewed as a threat to habitat complexity because of its stabilizing effect
on banks, which in turn leads to further channelization of the bed and
narrowing of the stream channel (Graf 1978, Valdez 1990, U.S. Fish and
Wildlife Service 1990). Flushing flows of some magnitude higher than
11,000 cfs, or perhaps of a longer duration, are evidently needed. At
present, we do not know the precise magnitude or duration of flushing
flows necessary that will prevent channelization and promote habitat
heterogeneity. Such studies are needed. However, it is clear that in the
upper Colorado River where sediment loads are high, flushing flows of
adequate magnitude and duration are needed to occur at a greater frequency
than that observed during recent years.
Spring Flow Effects on Young Fishes
Background
High spring flows also appear to be important in enhancing reproductive
success and/or survival of young of some native species, including Colora-
do squawfish. Haynes et al. (1984) sampled larval Colorado squawfish in
the upper Colorado River (Loma to the Colorado/Utah State line) during
1979-1981 and in the Yampa River during 1980-1981. In the Colorado River,
catch rates of larval Colorado squawfish were highest in 1979 and 1980,
years in which State-line peak flows were approximately 35,000 and 30,000
cfs, respectively. In both rivers, catch rates were lowest in 1981, a year
of low spring flows.. In the Colorado River, only one larvae was collected
in 1981 despite the highest sampling effort of the three years. Discharge
on the highest flow day of 1981 averaged 11,200 cfs at the Colorado/Utah
10