7145

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

ships. Other important variables, such as magnitude of summer flows and
temperature regimes are correlated with peak flows, and these in turn
could have a direct effect on larval production of some species or possi-
bly retainment of larvae within the study area (high summer flows might
facilitate long-distance transport of young). Thus, peak flows may be more
of an index to the type of water year rather than the controlling factor
itself. One possible direct-effect scenario for Colorado squawfish is that
some magnitude and duration of high flow may be necessary to prepare the
spawning substrate (Haynes et al. 1984). Though spawning may occur every
year, hatching success could vary depending on the degree to which the
cobble substrate is flushed of sediments. Results of studies on other
systems have demonstrated inverse relationships between accumulation of
fine sediment in fish spawning and rearing habitats versus fish survival
and abundance (Reiser et al. 1989). Studies are needed to determine the
importance of this variable for Colorado squawfish in the upper Colorado
River. Another possibility is that as numbers of non-natives increase in
years of low flow, predation-related mortality on squawfish might increase
(Valdez 7.990).
One might expect that numbers of larval Colorado squawfish transported out
of the reach via river currents would be higher in years of relatively
high summer flows, thus resulting in fewer YOY squawfish found in the
Grand Valley during fall of such years. Though flow effect on percent
larvae transported out of the reach is unknown, it is of interest to note
that total numbers of larvae and YOY were highest in 1986 despite,rela-
tively high summer flows that year (mean flow during August 1986 in the
18-mile reach downstream of the mouth of the Redlands power return, canal
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