9406

• UCREFRP Catalog Number: 9406
• Author: Osmundson, D. B.
• Title: Importance of the '15-Mile Reach' to Colorado River Populations of Endangered Colorado Pikeminnow and Razorback Sucker.
• USFW Year: 2000.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

tively large populations occupying quality
habitat) are believed critical for persistence
of metapopulations (Schoener 1991, Harri-
son 1991, 1994, Stanford et al. 1996). In
rivers, large alluvial reaches often support
core populations of fishes (Lichatowich and
Mobrand 1995). The current distribution of
Colorado pikeminnow and the historic
distribution of razorback sucker in the
upper Colorado River appears to fit this
model, with core populations centered in
the alluvial Grand Valley.
To understand the habitat needs of
Colorado pikeminnow and razorback suck-
er, an ecological perspective is required that
takes into account all phases of their life
cycles and recognizes that population dyna-
mics occur at a scale encompassing hun-
dreds of miles of river. Thus, the relative
importance of a particular area, such as the
15-mile reach, cannot be viewed in isola-
tion, but must be viewed in the context of
how it fits into the larger life history picture.
A river without good adult habitat cannot
support a viable population, just as a river
without good spawning or nursery habitat
cannot. The reach downstream of Moab,
Utah is critically important in a similar way,
because it contains the best nursery habitat
in the Colorado River. Failure to consider
these facts can lead to the false conclusion
that because the 15-mile reach constitutes
only 8% of the 185 occupied miles of the
Colorado River (above the Green River
confluence), it plays only a small role in
maintaining populations of Colorado pike-
minnow and razorback sucker. To the con-
trary, the data suggest that prime adult
habitat is restricted to the upper 60 miles of
this 185-mile-long Colorado River reach,
with the best habitat and greatest concentra-
tions of adults located in the 33-mile-long
Grand Valley. With this perspective, the
importance of the 15-mile reach becomes
apparent.
The Recovery Implementation Program
for Endangered Fish Species in the Upper
Colorado River Basin has plans to provide
fish passage at diversion structures up-
stream of the 15-mile reach to allow Colo-
rado pikeminnow and razorback sucker
access to upstream portions of their histori-
cal range. The 15-mile reach, and the short
3-mile reach just upstream, currently consti-
tute the upstream limit of the Colorado
pikeminnow's range in the mainstem Colo-
rado River. The Price-Stubb Dam has
blocked upstream movements offishes since
its construction in 1911. Razorback sucker
have been found upstream of these diver-
sions relatively recently; one was captured
in 1991 near Rifle, Colorado, some 55 miles
upstream of Palisade (Burdick 1992).
However, no similar upstream capture
records, either recent or historic, exist for
Colorado pikeminnow despite intensive
sampling from Price Stubb Dam to Rifle
during the past three decades (Kidd 1977,
1979; Valdez et al. 1982; Anderson 1997;
Osmundson 1999a). Numbers of pikemin-
now in this reach likely diminished over
time as a result of the long-term effects of
the diversion dams preventing return migra-
tion after larvae or adults moved down-
stream. Providing passage to this area
should prove beneficial to the Colorado
River population by increasing the amount
of adult habitat. Because adult habitat is in
short supply, the extent to which this up-
stream reach will provide suitable habitat
has a bearing on the relative importance of
the 15-mile reach.
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