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• UCREFRP Catalog Number: 7300
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes, Yampa River, Colorado.
• USFW Year: 1989.
• USFW - Doc Type: Biological Report 89‎(14)‎,
• Copyright Material: NO

500
.~, 400 1975
E
w 300
zoo
U 100
0
0
APRIL MAY JUNF JIAY AUB
.. 260
~ 200 1981
E
~, 150
i 100
U
0 50
0
APRIL MAY JUNE JULY AU6
e 400
19BB
E 300
200
U 100
v
0
APRLL MAY JUNF JULY AV6
180
H 1989
E 146
100
N 60
0
APRA. MAY JUNE JULY AV6
Fig. 14. Relation between discharge and spawning period for
razorback sucker, Yampa River, 1975, 1981, 1988, and
1989 (discharge data incomplete for 1989). Venical burs
delineate spawning period. (One collection of ripe fish in
1988.)
and the absence of juvenile and subadult life history
stages (McCarthy and Minckley 1987; Tyus 1987). The
apparent decline of the razorback sucker toward
extinction throughout the Colorado River basin
emphasizes the need for more immediate measures
toward recovery of this species.
Limiting Factors
An evaluation of limiting factors is difficult because
of complex relations between environmental and
biological variables that limit the distribution and
abundance of organisms. A limiting factor is simply one
component of a multidimensional system. Thus, single
factor studies (e.g., determination of temperature
threshold for successful reproduction) should be
evaluated from a holistic perspective for application in
natural systems and not in isolation. We stress the need
for system-level cognizance and interpretation in
evaluating factors that are potentially limiting to species
in decline.
Studies of factors limiting the distribution and
abundance of rare fishes in the Yampa River are
complicated by the variability of the environment (e.g.,
seasonal fluctuations in discharge, temperature, food
base, and species abundance) and by logistical problems
associated with studying fishes in large, turbid rivers.
The determination of limiting factors for rare fishes is
further complicated becatise of limited life history
information. Habitat use by the rare fishes may only
reflect temporary, seasonal, or marginal habitat
availability. Thus, caution must be exercised when
determining habitat needs and limiting factors for fishes
in decline, and professional biological judgment must be
recognized as critical in data interpretation.
Some factors that may be limiting the distribution and
abundance of rare fishes in the Yampa River are
summarized in Table 6. This information is presented
for consideration in future updates of the Sensitive
Areas report (Upper Colorado River Basin
Coordinating Committee 1984) and for aiding the
Recovery Implementation Program (U.S. Fish and
Wildlife Service 19$7) for the Yampa River. Each
species is discussed separately in the following sections.
Although more information is available regarding
habitat needs and limiting factors for the Colorado
squawfish, we do not suggest that protection of a single
species or a single life history stake will adequately
protect all-we emphasize that each species is unique
and has different requirements for survival.
Colorado Squawfish
An evaluation of factors limiting the distribution and
abundance of Colorado squawfish in the Green River
system is complex because of the wide range of habitat
and Flow conditions required by the different life history
stages. High spring flows, in addition to increasing
water temperatures, are necessary for the initiation of
the spawning migration (Figs. 7 and 8). Decreasing
flows and warming river temperatures in early and
mid-summer are necessary for successful spawn and
downstream transport of drifting larvae (Tyus et al.
1987; Fig. 11). Low flows in late summer and fall are
correlated with availability of nursery habitat and young
fish abundance and growth (Tyus et al. 1987; M.
Pucherelli and R. Clark, written communication). A
stable winter base-flow is necessary for maintenance of
winter habitats (Wick and Hawkins 1989).
Adult
The potamodromous migrations and homing
behavior of Colorado squawfish (Wick et al. 1983; Tyus
and McAda 1984; Tyus 1985) from downstream Green
River and upstream Yampa River to Yampa Canyon
mandates protection of known migration routes, since
feasibility of fish passage facilities for this species has yet
to be demonstrated. We presume that blockage of these
river sections by dams or water diversions will directly
result in the local extinction of Colorado squawfish
(Tyus 1984), as evidenced by the recent loss of 80 km of
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