7065

• UCREFRP Catalog Number: 7065
• Author: Behnke, R. J. and D. E. Benson.
• Title: Endangered and Threatened Fishes of the Upper Colorado River Basin.
• USFW Year: 1983.
• USFW - Doc Type: Bulletin 503A,
• Copyright Material: NO

it grows, fish become more important in itA diet.
After it reaches a length of about 8 inches, fish
become the predominant food.
The maximum age of squawfish collected in recent
years is about 10 to 12 years. The fish mature and
spawn at an age of 6 or 7 years and a length of 18 to
20 inches. Because no one has observed the spawning
of squawfish, the precise type of habitat selected
for spawning is not known. The finding of young
squawfish in quiet backwater areas suggests that
spawning takes place in river sections near the back-
water nursery habitat. Spawning occurs in early or
midsummer, when water temperatures reach about 700F.
It generally is believed that squawfish made major
spawning migrations before they were blocked by dams,
and that this behavior was the reason for their being
called "salmon." Adult squawfish favor deep areas of
large river channels from which they can move out to
adjacent reaches and feed on other fishes. Squawfish
and razorback suckers were the fish most highly valued
as food by the early settlers and miners in the Colo-
rado River basin. They were caught and marketed by
local commercial fishermen. When they were abundant,
squawfish were frequently caught on bait or lures by
anglers.
The nearest living relatives of the Colorado
River squawfish are three other species of squawfish
native to the Columbia River, Sacramento River, and
Oregon coastal rivers. None of the other species
reach a size comparable to that of the Colorado River
squawfish. The other species are not such strict
predators (feeding more readily on invertebrate ani-
mals), and occupy a wider variety of habitats. In
contrast to the Colorado River squawfish, the related
species are flourishing to such an extent that they
are considered a nuisance because they compete with
game fishes. When reservoirs are constructed in the
Columbia River basin, the Columbia squawfish often
becomes the dominant species, despite efforts to con-
trol its numbers. It responds in a most positive
manner to man's alteration of the environment and to
the presence of non-native fishes. Although the
general appeareance of all four species of squawfish
is similar, there obviously must be large differences
in life history and ecology between the Colorado River
squawfish and its relatives that have caused the Colo-
rado River squawfish to fare so poorly when subjected
to environmental change and non-native fishes.
Past and Present Distribution
Originally, the squawfish was found throughout
the Colorado River basin, in the mainstream channels
of the Colorado and Green rivers and the large tribu-
taries such as the Gila, San Juan, Gunnison, and Yampa.
Historically, the distribution of squawfish would
begin in the larger, warmer waters at lower eleva-
tion, at the lower limits of distribution of trout
and whitefish. The habitat of the squawfish was
originally shared with the bonytail chub, the flannel-
mouth sucker, and the razorback sucker. Negative
environmental changes causing the decline in squaw-
fish distribution and abundance can be grouped into
two categories: dramatic and catastrophic changes,
such as the creation of a large impoundment; and
gradual, cumulative changes from land and water use
practices influencing habitat through changing flow
regimes.
The advent of large mainstream dams, initiated
by Hoover Dam in 1930 and proceeding to the completion
of Glen Canyon and Flaming Gorge dams in 1963, caused a
rapid decline in squawfish abundance and distribu-
tion. Only one squawfish has been found in the entire
lower Colorado Colorado River basin since 1968. After
the closure of Flaming Gorge Dam and the subsequent
releases of cold water, squawfish were eliminated from
the upper Green River downstream to a point below the
confluence with the Yampa River. This section of the
Green River, from the Yampa River to the confluence
with the Colorado, is about 200 miles long and is
now the greatest stronghold of the squawfish. This is
the only area where successful reproduction
(as indicated by the collection of young fish 1 or 2
years old) has been consistently found in the past
few years. From 1975 through 1979 several adult
squawfish were found in the Yampa River, upstream to
a point above Juniper Canyon. In the White River,
adults were frequently found in the lower reaches in
Utah, and two were captured just above Piceance
Creek in Colorado. In the Gunnison River, a few
adult squawfish still occur in the lower reaches
near the town of Whitewater. A remnant population
may occur in the San Juan River between Lake Powell
and Navajo Reservoir in Utah and New Mexico. Squaw-
fish are found sporadically in the Colorado River up
to Plateau Creek, about 15 miles above Grand Junction.
In recent years many captures along the Colorado River
have been from gravel excavation ponds connected to
the main river.
Except in the Green River below Jensen, Utah, and
the Colorado River below Westwater Canyon, Utah,
there has been little evidence of successful
12