7758

• UCREFRP Catalog Number: 7758
• Author: Stanford, J. A. and P. C. Nelson.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin.
• USFW Year: 1994.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

6 BIOLOGICAL REPORT 24
of nonnative fishes that may migrate upstream,
thereby influencing the native fishes living in the
Upper Colorado River Basin. However, I viewed
Lake Powell as the downstream boundary of the
river ecosystem examined in this report (Fig. 1).
A vital characteristic of river ecosystems is that
their biophysical processes are inherently vari-
able. The essence of ecology is understanding the
complex processes that control observed variabil-
ity in the distribution and abundance of biota.
Quantification of the structure and function of
complex systems, like the Upper Colorado River
Basin ecosystem, in time and space must be based
on long-term (> 5 years) measurements to detect
patterns or trends that in shorter time frames are
overwhelmed by variability. Hence, an ecosystem
approach strives to determine how and why the
river changes in time and space, not simply to
describe current conditions.
Like most scientists, I view model building and
logistic descriptions of dynamic events in ecology
as mechanistic tools for formalizing a better under-
standing of what is known about a system; such
tools should not be used to predict the future.
Predicting the consequences of environmental
change is the ultimate challenge of contemporary
ecology. This must be resolved through strong in-
ferences based on properly scaled measurements
of biophysical variables that integrate the myriad
system-specific ecological processes that are spa-
tially and temporally dynamic (Magnuson 1990;
Stanford and Ward 1992a). The problem of in-
stream flow provision must be resolved from
strong inferences derived from long-term trends in
ecological processes and responses of the river
ecosystem in which the endangered fishes live.
River Ecology and Effects of
Regulation on the Endangered
Fishes of the Upper Colorado
River Basin
Ecology of the Endangered Fishes
Information about the endangered fishes is very
detailed, given that they are relatively rare fishes;
several reviews of the scientific information have
been published (e.g., Stanford and Ward 1986b;
Minckley et al. 1991; Tyus 1991a). Therefore, I
repeat here only salient points of particular impor-
tance to my review of the flow recommendations
made by the U.S. Fish and Wildlife Service.
As noted above, the historical range of the four
species included the potamon and transitional
reaches of the Green and Colorado river systems,
including most of the larger tributaries, in particu-
lar the Yampa, White, Dolores, and Gunnison riv-
ers. Today, ranges of these fish are fragmented by
dams and diversions, and populations have de-
clined significantly in relation to distributions at
the turn of the century (Quartarone 1993).
Bonytail chub are close to extirpation, but they
have been successfully cultured, along with hump-
back chub, squawfish, and razorback sucker, at the
Dexter National Fish Hatchery, Dexter, New Mex-
ico (Johnson and Jensen 1991), and brood stocks
currently are being held in several locations. Be-
cause of their comparative rarity in the wild, eco-
logical information on the historical range of
bonytail chub is more fragmentary than for the
other species. A few specimens of bonytail chub
were collected in the 1970's in the Green and
Yampa rivers (Kaeding et al. 1986), but their phe-
nology (life history) and exact cause of disappear-
ance in the Upper Colorado River Basin system are
unknown.
Humpback chub are found only in whitewater
canyon segments (Fig. 1). Migrations are limited,
and humpback chub may have always been re-
stricted to specific canyon segments, at least as
adults. Spawning in the Upper Colorado River Ba-
sin occurs on the declining limb of the spring runoff
event in association with the 20° C isotherm
(Kaeding and Zimmerman 1983). Humpback chub
interact behaviorally (and probably hybridize) with
congeneric, endemic roundtail chub (Gila robusta),
which are more abundant throughout the Upper
Colorado River Basin (Kaeding et al. 1990; Karp
and Tyus 1990). Much of what is known about the
life cycle of humpback chub is based on unpublished
studies in the Grand Canyon, where they migrate
from the regulated Colorado River into the unregu-
lated Little Colorado River to spawn. Similar mi-
gratory behavior has not been documented in the
Upper Colorado River Basin, and exact locations of
spawning sites are unknown (Richard Valdez,
BioWest Inc., Logan, Utah, personal communica-
tion; Larry Crist, U.S. Bureau of Reclamation, Salt
Lake City, Utah, personal communication).
Lanigan and Tyus (1989) estimated that only
978 ± 232 adult razorback sucker remained in the
Green River above Desolation Canyon during
1981-86, which very likely is only a small fraction
of the historic population. Some researchers be-
lieve that significant declines have occurred since