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

Figure l.--Mature Colorado Squawfish captured in
the mainstem Colorado River, Moffat County,
Colorado. Specimen was approximately 3 ft
(total length) and 18 lb.

~. lucius would be an adaptive evolutionary
response to a widely fluctuating riverine envir-
onment which might select for a species that
would grow larger and live longer to produce a
large number of offspring during desirable wet
years. Such a strategy would confer more posi-
tive adaptations than one of smaller size and
early reproduction, particularly in a large-river
ecosystem such as the Colorado drainage.

Historically, Colorado squawfish were distributed
throughout the Colorado River drainage from the
Green River in Wyoming to the Gulf of California
(Sea of Cortez). The species apparently began to
suffer declines in the mid-1930's where, hereto-
fore, it had been abundant enough to support
local indigenous and commercial fisheries
(Minckley 1973). ~. lucius, an obligate riverine
species, was apparently unable to adapt to the
massive habitat alteration that accompanied the
construction of several mainstem dams in the
lower basin, beginning with the completion of
Hoover Dam in 1935 and was functionally extir-
pated from the lower Colorado River mainstem and
its Gila and Salt River tributaries by the early
to mid-1960's (Holden 1979). It now persists
largely in relatively undeveloped areas of the
upper Colorado River basin above Lee's Ferry,
Arizona, and it is presently listed as
"endangered" by the United States Department of
the Interior throughout its historic range and
by the State of Colorado.

As is the case with so many "nonresource" species
(adopting the relevant terminology of Ehrenfeld
1976), little specific life-history or population
information was known prior to the initiation of
the studies which are the subject of this paper.
Squawfish are the top native carnivore in the
Colorado River system (they now receive compe-
tition from a number of introduced exotic
predators) and are believed to be exclusively
pisciverous above approximately 8 in. in length
(Vanicek and Kramer 1969). Studies by Vanicek

and Kramer (1969), 1101 den (197)), and Seethaler
(1978), among the 1II0re notable, documented that
mature Colorado squawfish were widespread but
nowhere abundant in the Green and Yampa River
system of northeast Utah and adjacent northwest
Colorado and were typically associated with deep
pools and a variety of substrates. Juveniles
were captured in shallow shoreline embayments
over silt substrate. Reproduction, based upon
the capture of ripe adults was assumed to coin-
cide with decreasing flows and rising summer
water temperatures that are characteristic of
snowmelt-driven southwestern rivers.

Unquestionably, these researchers were observing
the long-term impacts of one of the gravest
misjudgments ever made in recent western
fisheries management, i.e., the Green River
rotenone program carried out in 1962 in conjunc-
tion with the closure of Flaming Gorge Dam in
northeastern Utah. Large numbers of Colorado
squawfish, in addition to several other native
species, were eliminated from over 250 mi of the
mainstem Green River to create a non self-
sustaining salmonid fishery (Minckley and Deacon
1968). A similar program was conducted on the
San Juan River with the closure of Navajo Dam in
New Mexico. Although the long-term meaningful-
ness of such poisoning losses is arguable, the
loss of habitat to cold reservoir tailwaters and
long lacustrine reservoir reaches unquestionably
contributed to the continued decline of the
Colorado squawfish in the upper basin (Colorado
River Fishes Recovery Team 1978).

In addition to the unfavorable riverine and
reservoir habitats created during the 1960's
period of dam building in the upper basin, the
dams themselves served as enormous barriers to a
species that, due to its reported migration
habits, was sometimes referred to as the "white
salmon of the Colorado" (Holden 1979; Tyus
1984b). At the same time, flows of the upper
basin have been continuously diverted to eastern
Colorado by more than 40 transmountain diversions
and substantial quantities of water have been
lost to evaporation in reservoirs and via irri-
gation. Such regulatory and consumptive prac-
tices have resulted in an upper basin ecosystem
that is altered both in terms of water quantity
and out of phase relative to historical seasonal
cycles (Bishop and Porcella 1976). Clearly, the
Colorado squawfish is faced with an ecosystem
that is at variance in several major respects
from that in which it evolved and at present, the
species appears to be restricted to about 25% of
its former range (fig. 2)(Tyus 1984b).

LOWER YAMPA RIVER RESEARCH: 1980-PRESENT

It is relevant to have an understanding of the
state of knowledge relative of the ecology of
the Colorado squawfish in the upper basin prior
to the initiation of lower Yampa River studies in
1980. The distribution of the species in the
upper basin was fairly well understood as a
result of studies in the mid-1960's through the
late 1970's by Banks (1964), Vanicek (1967),

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