7163

• UCREFRP Catalog Number: 7163
• Author: Haynes, C. M. and J. R. Bennett.
• Title: Relationship between the Preservation of Wilderness Values and Endangered Species
• USFW Year: 1985.
• USFW - Doc Type: A Case-Study from the Upper Colorado River Basin, U.S.A.
• Copyright Material: YES

SYNTHESIS: MANAGEMENT IMPLICATIONS

The Colorado squawfish is a top-level carnivore
which requires a diversity of habitat variables
and a large range to fulfill its life requisites.
While feeding and overwintering may be accom-
plished in several areas, reproduction appears to
require specific conditions that are available in
only a few selected reaches. Migrations in the
upper Green and Yampa Rivers coincide with warm-
ing conditions during spring runoff and spawning
appears limited to a relatively short reach of
the lower Yampa River in Dinosaur National
Monument. Peak spawning activity apparently
occurs at water temperatures of approximately
22-25 C, although limited spawning occurs both
above and below this range. Following spawning
in the Yampa, primarily at RM 16-20, adults
appear to return to their premigratory locations,
often >100 mi away--some moving upstream, others
moving downstream. Eggs hatch in 3.75-6.0 days
(Hamman 1981) and protolarvae of 0.24-0.29 in.
(total length) spend 22-96 hrs in the cobble
prior to swim-up, at which time they may be swept
into the currents to be transported down the
Yampa River. An unknown proportion of squawfish
larvae deposited in quiet shoreline embayments by
countercurrents are subjected to predation, com-
petition, heating, desiccation, and in winter,
freezing. Hypothetically. it is to the advantage
of squawfish larvae to be rapidly transported out
of Yampa Canyon to more permanent, structurally
diverse backwaters in Utah's upper Green River
(Haynes and Muth, in prep.).

Based upon complementary CRFP-DOW studies, larval
production in the lower Yampa River may indeed
drive the entire upper Green River system above
Gray Canyon, Utah. A second spawning site in the
lower Green River appears to support an inde-
pendent spawning sub-population (fig. 4).
Similar studies on the mainstem Colorado River
have not yielded similar results, although larvae
have been collected (Haynes and others 1984;
Haynes and Muth 1985), and adult migrations do
not appear to be as pronounced there. It is
possible that the perturbed mainstem and its
other tributaries no longer offer the necessary
combination of habitat variables found in the
relatively unaltered lower Yampa. This is
clearly a case for continued radiotelemetry
studies.

Unquestionably, the relatively unaltered lower
Yampa River in Dinosaur National Monument still
retains the natural features essential to
Colorado squawfish production for a major portion
of the upper Colorado River basin and the protec-
tion of this vital area appears critical to the
long-term survival of the endangered Colorado
squawfish. Any river development above or below
this short reach must consider the maintenance of
migrational corridors, sufficient spring flows to
flush spawning areas of sands and silts accumu-
lated during previous base flow periods, and the
water temperatures which are conducive to spawn-
ing, egg maturation and hatching. Furthermore,
because spawners originate both upstream and
downstream from the area, migrational routes must
be maintained in both directions; otherwise

WYOMING

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Figure 4.--Confirmed spawning (black) and nursery
(shaded) locations for the Colorado squawfish in
the upper Colorado River basin. As is the case
for lower Yampa Canyon, the Gray Canyon spawning
area retains much of its wilderness character
(after Tyus 1984b).

spawning could be limited to individuals from a
single area, thereby adversely affecting the
future genetic vitality of the species.

A major bottleneck to the well-being of the upper
Green River squawfish may exist at the mouth of
the Yampa River. At the confluence with the dam-
regulated Green River, drifting squawfish larvae
are confronted with water temperatures that can,
for short periods, be as much as 10 C colder than
the natal Yampa. The potential impact on minute
squawfish proto larvae requires evaluation.
Further, during the wet year of 1983 when larval
production appeared relatively high, observations
at upper Green River nursery areas in Utah
suggest that larvae perhaps did not reach these
areas in numbers as high as in 1981-82 (H. Tyus,
pers. comm.). If this perceived high mortality
of the 1983 year-class is ultimately linked to
reduced water temperatures in the Green during
downstream transport or to some other combination
of factors resulting from high releases from
Flaming Gorge Dam, the management plan for the
reservoir should be modified to reduce or
eliminate these impacts.

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