My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
7601
CWCB
>
UCREFRP
>
Public
>
7601
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
7/14/2009 5:02:30 PM
Creation date
5/20/2009 3:10:36 PM
Metadata
Fields
Template:
UCREFRP
UCREFRP Catalog Number
7601
Author
Minckley, W. L.
Title
Native Fishes of Arid Lands
USFW Year
1991.
USFW - Doc Type
A Dwindling Resource of the Desert Southwest.
Copyright Material
NO
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
52
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
Show annotations
View images
View plain text
<br />Native Fishes ln Arid Lands: <br />A Dwindling Resource of the Desert Southwest <br /> <br />Photographs by John N. Rinne <br /> <br />INTRODUCTION <br /> <br />The American Southwest is usually defined to <br />include all or part of 12 States in western United <br />States and Mexico (Fig. 1), much of which is <br />lowland desert interrupted and diversified by isolated <br />mountains and plateaus. Evaporation exceeds <br />precipitation so greatly that surface water should the- <br />oretically not exist. Nonetheless, major rivers such as <br />the Colorado and Yaqui formerly collected sufficient <br />water to flow all the way through the arid lowlands <br />to the sea. <br />Just a few decades ago, western streams swarmed <br />with fishes that had survived millennia of remarkable <br />geologic and climatic changes. They had adapted to <br />survive the special conditions in canyon-bound rivers <br />that varied from raging torrents in flood to isolated <br />pools in drought. Some had specialized to withstand <br />high summer temperatures and salts concentrated by <br />evaporation in desert lakes and marshes. However, <br />when technological humans moved in droves to the <br />warm, arid region, native fishes began to disappear. <br />Bumans need lots of water too, and typically far <br />more than required to support native fishes. <br />Early diversions for mineral and cattle production <br />and irrigated agriculture were followed by giant <br />mainstream dams that not only stored and controlled <br />runoff, but produced electricity as well. This abun- <br />dant source of power led to expansion of industry, <br />and to retirement communities, recreation, and more <br />urbanization-the "Sun Belt" enterprises of today. <br />All these demand water for drinking, watering lawns <br />and golf courses, and other uses-as well as for <br />more and more electrical power. <br />As a result, native fishes are being exterminated. <br />Destruction of aquatic habitats, changes from natural <br />to artificial conditions, and predation and competi- <br />tion by alien species enhanced by artificial condi- <br />tions, all combine to destroy them. Many are nearing <br />extinction, some are already gone, and neither legis- <br />lation, nor determined attempts at conservation by <br />agency, academic, and other managers has succeeded <br />in reversing the trend. The only chance seems to lie <br />in an emergence of public opinion that recognizes <br />native fishes as valuable resources and demands their <br />conservatlOn. <br /> <br />Text by W. 1. Minckley <br /> <br />THE SETTING <br /> <br />Elevations in the region vary from sea level to <br />more than 3600 m. Precipitation is equally variable, <br />averaging less than 5.0 cm per year in the most <br />severe desert, to more than 128 cm at the higher <br />elevations. Most of the vegetation zones of North <br />America are represented, from patches of tundra on <br />the highest peaks, downhill through extensive conifer <br />forests then woodlands and grasslands, to end with <br />desertscrub on the basin floors. <br />The region is also hydrologically complex. Most <br />major drainage basins are composites of once- <br />independent systems brought together by crustal <br />movements or volcanic activity. Most of the Sonoran <br />Desert region, emphasized here, is characterized by <br />through-flowing rivers passing from mountains to the <br />sea. Closed basins (Fig. 2), from which water escapes <br />only through evaporation or seepage, are common in <br />the Mohave, Great Basin, and Chihuahuan deserts. <br />Coverage is restricted to watersheds west of the <br />Continental Divide, which ultimately drain to the <br />Pacific Ocean through the Colorado River, Rio <br />Yaqui, and lesser streams between those two major <br />basins (Fig. 1). <br /> <br />Origins of the Desertlands <br /> <br />Desert conditions are new, in geologic time, to <br />much of this area. Studies of fossil plants and <br />animals have convincingly demonstrated that only a <br />few thousand years ago woodlands and prairies <br />flourished where desert now exists. Because trees and <br />grasses require more water than cacti and shrubs, <br />available precipitation and runoff were either greater <br />in amount, far different in distribution throughout <br />the year, or both. Cycles of drying alternating with <br />periods of substantial moisture have progressed <br />toward more and more frequent and severe drought. <br />The region is now more arid than ever before. <br />Over a longer time scale, complex geologic activity <br />shaped the land surface to help set the stage for <br />development of southwestern deserts. The coastlines <br />of Mexico and California slid northwest along the <br />San Andreas and related faults in response to <br /> <br />1 <br />
The URL can be used to link to this page
Your browser does not support the video tag.