9420

• UCREFRP Catalog Number: 9420
• Author: Maddux, H. R., J. A. Mizzi, S. J. Werdon and L. A. Fitzpatrick.
• Title: Overview of the Proposed Critical Habitat for the Endangered and Threatened fishes of the Virgin River Basin.
• USFW Year: 1995.
• USFW - Doc Type: Salt Lake City.
• Copyright Material: NO

PART I -GENERAL OVERVIEW
Background
The three listed fishes aze endemic to the Virgin River Basin. The Virgin River flows
generally along the Hurricane Fault, which forms the boundary between the Colorado Plateau
and the Great Basin. These two geologic features are quite dissimilar. The Colorado
Plateau is characterized by horizontal-lying strata eroded into canyons, plateaus, and mesas.
Long, isolated mountain ranges sepazated by broad alluvial valleys typify the Great Basin
province. The Virgin River flows southwest through southwestern Utah, northwestern
Arizona, and southeastern Nevada for approximately 320 kilometers (km} [200 miles (mi)]
before flowing into Lake Mead. Prior to the completion of Boulder (Hoover) Dam in 1935,
the Muddy (=Moapa} River, in southeastern Nevada, joined the Virgin River before the
latter flowed into the Colorado River. These two rivers now flow sepazately into the
Overton Arm of Lake Mead.
The Virgin River listed fishes populations have declined due to the cumulative affects of
environmental impacts that have resulted in habitat loss including: dewatering from
numerous diversions; proliferation of nonnative fishes; and alterations to natural flow,
temperature, and sediment regimes.
There is considerable overlap in critical habitat proposed for the three species, and the
proposed designation of a total of 330.8 km (206.8 mi) for the Virgin River listed fishes
includes portions of Utah, Arizona, and Nevada. The Service proposed 151.7 km (94.8 mi)
of critical habitat for the woundfm (approximately 13.5 percent of its historical range); 151.7
km (94.8 mi) for the Virgin River chub (70.8 percent of its historical range); and 201.9.km
(126.2 mi) for the Virgin spinedace (87.3 percent of its historical range).
Woundfm
On the basis of early records, the original range of woundfm extended from near the
confluence of the Salt and Verde Rivers at Tempe, Arizona, to the mouth of the Gila River
at Yuma, Arizona (Gilbert and Scofield 1898) (Figure 1). Woundfm were also likely found
in the mainstem Colorado River from Yuma (Jordan and Evermann 1896, Meek 1904,
Follett 1961) upstream to the Virgin River in Nevada, Arizona, and Utah, and into La
Verkin Creek, a tributary to the Virgin River in Utah (Gilbert and Scofield 1898, Snyder
1915, Miller and Hubbs 1960, Cross 1975). However, from biological considerations alone,
there is reason to believe that woundfm occurred further upstream on the Verde, Salt, and
Gila Rivers in Arizona.
Woundfm are believed to be extirpated from most of their historical range except the
mainstem Virgin River. Woundfm presently range from Pah Tempe Springs (also called La
Verkin Springs) on the mainstem of the Virgin River and the lower portion of La Verkin
Creek in Utah, downstream to Lake Mead. A single specimen was taken from the middle
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