Vegas - Virgin



ID

129

Author(s)

Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA. Additional text provided by Jennifer Hales.


Countries

United States

Major Habitat Type

Xeric freshwaters and endorheic (closed) basins

Drainages flowing into

The Virgin River naturally flows into the Colorado, but today flows into Lake Mead, as does the Moapa River (Williams et al. 1985).


Main rivers to other water bodies

The main watersheds are those of the White River, Moapa River, Meadow Valley Wash, and the Virgin River. The White River was a tributary to the Colorado River during pluvial times but is now dry for much of its length.



Description

Boundaries

This ecoregion is centered in southeastern Nevada, and also occupies the extreme northwestern corner of Arizona and the southwestern corner of Utah. Though nestled in between ecoregions of the Great Basin, this ecoregion is part of the Colorado complex, as its waters historically drained into the Colorado River.

Topography

This ecoregion is rugged, with high mountains surrounding broad alluvial valleys. Elevations range from 400 to 3000 m.

Freshwater habitats

Many of the streams are ephemeral, and the more permanent habitats are associated with springs. Three spring-fed habitats stand out in this ecoregion for their biotic distinctiveness and diverse habitats. The upper White River basin is largely desiccated, but a short stream is fed by a series of springs and outflow creeks, each with their own characteristic physiochemistry and temperature. Pahranagat Valley, located further south along the intermittent White River, is distinguished by Hiko, Crystal, and Ash Springs and their outflow creeks. The 40-km long Moapa River flows from more than 20 warm springs, traverses through blackbrush and creosote communities, and supports important riparian zone biota (Williams et al. 1985).

Terrestrial habitats

The ecoregion lies in the south-central part of the Great Basin shrub steppe, the Colorado Plateau shrublands and the northeastern edge of the Mojave Desert terrestrial ecoregions. It is characterized by woodland vegetation, shrub-grass and desert-shrub, with some dominant species including sagebrush (Artemisia) and saltbrush (Atriplex) (Ceratoides lanata) (Turner 1994).

Description of endemic fishes

Endemic fish historically present in the ecoregion’s freshwater habitats are the White River spinedace (Lepidomeda albivallis) of the upper White River; the Virgin River spinedace (L. mollispinis mollispinis) of the Virgin River; the Big Spring spinedace (L. mollispinis pratensis) of Big Spring in Meadow Valley Wash; the Moapa speckled dace (Moapa coriacea) in the Moapa River headwaters; and the Virgin chub (Gila seminude).

Other noteworthy fishes

Other noteworthy fishes include the extinct Las Vegas dace (Rhinichthys deaconi) in springs and outflows along Las Vegas Creek; Moorman springfish (Crenichthys baileyi thermophilus) in the warm springs of the White River and Moapa River basins; Preston springfish (C. b. albivallis); White River springfish (C. b. baileyi); Hiko springfish (C. b. grandis); and Moapa springfish (C. b. moapae). Endemic subspecies of roundtail chub (Gila robusta seminuda), speckled dace (Rhinichthys osculus velifer), and desert sucker (Catostomus clarki intermedius) are recognized as well (Williams et al. 1985; Page & Burr 1991; Sigler & Sigler 1994).

Ecological phenomena

 

Justification for delineation

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).


References

  • Abell, R.,Olson, D.,Dinerstein, E.,Hurley, P. T.,Diggs, J. T.,Eichbaum, W.,Walters, S.,Wettengel, W.,Allnutt, T.,Loucks, C. J.;Hedao, P. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.
  • Minckley, W. L., Hendrickson, D. A. and Bond, C. E. (1986). "Geography of western North American freshwater fishes: Description and relationships to intracontinental tectonism" C. H. Hocutt and E. O. Wiley (Ed.) The zoogeography of North American freshwater fishes New York: John Wiley.
  • Williams, J. E., Bowman, D. B., Brooks, J. E., et al. (1985). "Endangered aquatic ecosystems in North American deserts with a list of vanishing fishes of the region" Journal of the Arizona-Nevada Academy of Sciences 20 pp. 1-62.
  • Sigler, J. W. and Sigler, W. F. (1994). "Fishes of the Great Basin and Colorado Plateau: Past and present forms" K. T. Harper, L. L. St. Clair, K. H. Thornes and W. M. Hess (Ed.) Natural history of the Colorado Plateau and Great Basin Niwot: University of Colorado Press.
  • Maxwell, J. R., Edwards, C. J., Jensen, M. E., et al. (1995) \A hierarchical framework of aquatic ecological units in North America (Nearctic Zone)\ St. Paul, MN. North Central Forest Experiment Station, USDA Forest Service.
  • Bailey, R. G. (1995) \Description of the ecoregions of the United States\ (Washington DC)
  • Page, L. M., and B. M. Burr (1991). "A field guide to freshwater fishes: North America north of Mexico" New York, NY: Houghton Mifflin Co..
  • Turner, J. T. (1994). "Great Basin Desertscrub" D. E. Brown (Ed.) Biotic communities in southwestern United States and northwestern Mexico ( pp. 145-155 ) Salt Lake City, UT: Univerisity of Utah Press.