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WSPC04553
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Last modified
1/26/2010 11:40:00 AM
Creation date
10/9/2006 4:40:35 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8240.200.10.H
Description
Colorado River Threatened-Endangered - UCRBRIP - Program Organization-Mission - Stocking
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
4/29/1996
Author
Tyus and Saunders
Title
Non-Native Fishes in Natural Ecosystems and a Strategic Plan for Control of Non-Natives in the Upper Colorado River Basin - 04-29-96
Water Supply Pro - Doc Type
Report/Study
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<br />UJ2476 <br /> <br />Bluehead sucker (Catostomus discobo/us) populations also may be declining, They <br />are uncommon to rare in many mainstream habitats in the upper basin (Tyus et al. <br />1982), and may once have been more widely distributed. More species may be <br />experiencing decline, but thorough study has been constrained by a lack of institutional <br />interest and, therefore, funding. <br /> <br />The decline of native fishes in the lower basin has been extensive and the <br />endemic fauna of the main channel is almost gone. It has been replaced by a new <br />fauna consisting of about 44 forms (Minckley 1982), many of which were introduced <br />from more mesic environments and apparently better suited (i.e. "preadapted"; Taylor <br />et al. 1984) to the new conditions in the Colorado River basin. Many of the successful <br />introduced species had certain attributes that enabled rapid colonization and <br />population growth in these novel environments (Taylor et al. 1984). About 20 of these <br />species are abundant locally or regionally. In the upper basin, more natural conditions <br />support most of the native fishes, but 42 introduced fish species or subspecies occur <br />and 10 of these are considered abundant (Tyus et al. 1982). <br /> <br />Habitat of the native Colorado River fish fauna has been greatly changed during <br />the last 100 years by physical habitat alterations and the introduction of nonnative <br />species. Alterations to the physical environment have been described elsewhere and <br />resulted from construction of water development projects that began in the early 1900s <br />(Fradkin 1984, Carlson and Muth 1989). By the 1960s, much of the mainstream river <br />had been converted into a system of dams and diversions (Figure 2). As a result, <br />extensive flow regulation substantially altered the timing, duration, and magnitude of <br />annual flood flows. The large floods that were once normal in the Colorado River are <br />now controlled by more than 50 mainstream dams and major diversions. These <br />structures have caused changes in water temperature, sediment load, nutrient <br />transport, and other facets of water quality (Carlson and Muth 1989), For example, silt <br />load in some reaches has been reduced 90% (Fradkin 1984). Thus, most existing <br />mainstream habitats are now different than the historic habitats in which the native <br />fishes evolved. <br /> <br />Physical changes in the riverine habitat were accompanied by the introduction <br />and proliferation of nonnative species, and concomitant declines in native species. <br />Some introduced fishes have become very successful under the environmental <br />conditions that now prevail in the Colorado River system. These fishes may compete <br />with native species for food and space in some habitats. Although the native fishes <br />were well adapted to their natural environment, conditions may have been tilted in favor <br />of the introduced species by major environmental changes. For example, introduced <br />visual predators may have benefited from the reduction in turbidity that is the result of <br />new impoundments. The big river fishes evolved in turbid conditions and lack <br />evolutionary "experience" with the introduced predators. <br /> <br />6 <br />
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