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Last modified
7/14/2009 5:02:33 PM
Creation date
5/24/2009 7:10:41 AM
Metadata
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UCREFRP
UCREFRP Catalog Number
8204
Author
Tyus, H. M.
Title
Razorback Sucker (Xyrauchen texanus) Recovery Plan.
USFW Year
1998.
USFW - Doc Type
Boulder, Colorado.
Copyright Material
NO
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contaminants. In addition, there were significant differences in the endocrine systems <br />of both female and male fish attributed to exposure to compounds that alter the function <br />of the endocrine system associated with reproduction and recruitment. Due to a lack <br />of mixing in Las Vegas Wash within Lake Mead (LaBounty and Horn 1997), there is <br />concern that these contaminants are also being transported downstream into the <br />mainstream Lower Colorado River. The discovery of perchlorates, likely originating <br />from Lake Mead, as far downstream as Lake Havasu (R.D. Williams, personal <br />communication, 1998), suggests that contaminant problems in Lake Mead may pose a <br />threat to razorback sucker recovery downstream. <br />Changes in the Biological Environment <br />In many areas, nonnative fishes are the most significant threat to survival of the <br />razorback sucker. Nearly 70 nonnative fish species have been introduced actively or <br />passively into the Colorado River system during the last 100 years (Minckley 1982, <br />Tyus et al. 1982, Carlson and Muth 1989, Minckley and Deacon 1991, Maddux et al. <br />1993). As demonstrated by Moyle and Light (1996) biotic resistance to invasions by <br />native fishes appears to play only a small part in limiting the success of invading <br />species. More important appears to be the suitability of the hydrologic regime and <br />perhaps other physicochemical factors. In natural systems, rapid extinctions of native <br />fishes seldom occur. However, some invading species may be "preadapted" to <br />changed conditions, and native fish populations can be extirpated from waters that <br />have been greatly modified by humans. Such extirpations can be anticipated where <br />native populations have been "depleted, disrupted or stressed" (Moyle and Light 1996). <br />Creation of the US Fish Commission in 1872 is thought to be the beginning of <br />organized stocking initiatives for the Colorado River basin (Miller 1961). The original <br />motivation for fish stocking included, among other justifications, an attempt to "benefit" <br />the relatively "depauperate" Colorado River fauna (e.g., Jordan 1891). Several species <br />including common carp, channel catfish, and largemouth bass were introduced prior to <br />1900 (e.g., Wiltzius 1985). In the two decades prior to 1950, at least 36 fish species, <br />mostly game fishes from the eastern US, were introduced in the basin (Miller 1961). By <br />1980, more than 50 nonnative species had been actively introduced into rivers and <br />reservoirs of the Colorado River basin (Minckley 1982, Tyus et al. 1982, Carlson and <br />Muth 1989). <br />The primary reason for most intentional introductions was the desire to expand or <br />enhance sport fishing opportunities. Other reasons for fish introductions include <br />providing forage fish for game species, biological control of unwanted pests, and <br />aesthetic or ornamental purposes (reviewed by Taylor et al. 1984). Even though most <br />stocking in the river channels has been curtailed, nonnative fishes continue to enter the <br />river channel through escapement from adjacent water bodies or by recruitment from <br />the mainstream populations (Tyus and Saunders 1996). <br />20 <br />
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