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118 Status of Razorback Sucker
<br />Pimm (1986) stated that, outside of island environ-
<br />ments, nonnative vertebrate introductions have rarely
<br />eliminated native species and that elimination in a com-
<br />munity is more likely a result of predation rather than
<br />competition. It is possible, however, that the razorback
<br />sucker population could be limited by nonnative preda-
<br />tion on early life stages (Johnson et al. 1993) in the
<br />Green River because historically important floodplain
<br />habitats have been eliminated. High discharge may pro-
<br />vide habitat necessary for recruitment and may offset
<br />predation by nonnative fishes. High flows also inundate
<br />floodplains seasonally, thereby increasing production
<br />and food availability for the early life stages of fish (Junk
<br />et al. 1989; Welcomme 1989). In addition, evidence sug-
<br />gests that high spring flows in the upper Colorado River
<br />Basin appear to reduce nonnative cyprinids (Valdez
<br />1990; Osmundson & Kaeding 1991) that may prey on
<br />larval razorback suckers. A few months of enhanced
<br />food supply may greatly reduce the vulnerability to pre-
<br />dation of razorback suckers because their body size in-
<br />creases faster than that of most sympatric fish species
<br />(Hinckley et al. 1991). Without sufficient flows to recon-
<br />nect floodplain habitats to the main channel, it is un-
<br />likely that razorback sucker recruitment will continue.
<br />Restoration efforts should focus on defining the relation-
<br />ships of flooded bottomlands to razorback sucker
<br />growth and survival and how these areas can be man-
<br />aged to maximize productivity and reduce the effects of
<br />nonnative species.
<br />Acknowledgments
<br />The U.S. Fish and Wildlife Service, Recovery Implemen-
<br />tation Program for the Recovery of Endangered Fishes in
<br />the upper Colorado River Basin, and the National Park
<br />Service provided financial support for the collection and
<br />analysis of data. Wendell L. Hinckley, Harold M. Tyus,
<br />Peter B. Bayley, and G. Bruce Haines reviewed earlier
<br />drafts of this manuscript and provided helpful criticism.
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<br />Conservation Biology
<br />Volume 1Q No. 1, February 1996
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