|
<br />J.DOZ 5LL..;~ e--(\
<br />
<br />0"
<br />
<br />i
<br />.
<br />
<br />Western North American Naturalist 68(1), @ 2008, pp, 15-20
<br />
<br />EFFECTS OF WATER TEMPERATURE ON GROWTH OF
<br />RAZORBACK SUCKER LARVAE
<br />
<br />Kevin R. Bestgen1
<br />
<br />ABSTRAC1:-1 conducted laboratory expeliments and fit a response surface regression model to evaluate growth of
<br />endangered razorback sucker (Xyrauclwn texanus) up to 37 days post-hatch, Fish growth at ad libitum ration was posi-
<br />tively related to water temperature, and Imvae reared at 25,50C grew about l:\vice as fast in length and 4 times as fast in
<br />weight as those at 16.50C, Growth was intermediate at 19.5"C and 22.50C, Time required for razorback sucker larvae to
<br />exceed 25 mm total length (TL), a potentially important threshold ie" reduced predation, was 30 days (post-hatch) at
<br />25SC, 33 days at 22,5"C, 36 days at 19,50C, and 41 days at 16,5"C. Time to exceed 25 mm TL increased to 52 days
<br />under a low growth rate of 0.29 mm . d-1 Faster growth rates could reduce the time that razorback sucker larvae are
<br />vulnerable to predation by abundant and co-occurring small-bodied fish and invertebrate predators in nursery areas,
<br />Growth of razorback sucker larvae could be enhanced if flow re-regulation at Flaming Gorge Dam and downstreanl
<br />levee removal restored connections bel:\veen the Green River and its floodplain and increased availability of warm and
<br />productive wetlands,
<br />
<br />Key words: razorback sucker, temperature, growth, survival, regulated river, predation, wetland, endangered species,
<br />
<br />Rivers regulated by dams often exhibit
<br />altered flow and temperature regimes and en-
<br />hanced populations of nonnative fishes, which
<br />collectively result in reductions of native kinds
<br />(Carlson and Muth 1989, Poff et aI. 1997). Pre-
<br />scription of more natural regimes, including
<br />increased frequency of high flows that overtop
<br />the main channel, may restore portions of the
<br />native fish community that use the seasonally
<br />inundated floodplain (Stanford et al. 1996, Poff
<br />et aI. 1997, Muth et at. 2000). Early life stages
<br />of endangered razorback sucker (Xyrauchen
<br />texanus), an endemic of streams in the highly
<br />regulated Colorado River Basin in the Amed-
<br />can Southwest, use floodplain wetlands in the
<br />Green River Basin, Utah, for readng (Minck-
<br />ley et al. 1991, Modde 1996, Modde et al.
<br />1996, 2001). Survival and recruitment of
<br />razorback sucker larvae produced in the rnain-
<br />stem Green lliver-the only remaining river-
<br />ine population of razorback sucker that con-
<br />sistently produces substantial numbers of
<br />young-may be linked to availability of down-
<br />stream low-velocity floodplain areas, where
<br />relatively warm and food-dch conditions may
<br />promote faster growth and higher survival of
<br />larvae (Bestgen 1990, Tyus and Karp 1990,
<br />Modde 1996, Clarkson and Childs 20(Xl, Modde
<br />et al. 2001, Bestgen et al. 2002). Floodplain
<br />
<br />access is thought to be important because
<br />razorback suckers in the Green River spa"vn
<br />during spring high-flow periods in the main
<br />channel, where low water temperatures of 120_
<br />160C and low food availability may limit growth
<br />in the few in-channel low-velocity reming areas
<br />(Tyus and Karp 1989, 1990, Bestgen 1990,
<br />Mabey 1993, Muth et aI. 20(0). Access to high
<br />growth environments is sometimes limited be-
<br />cause levees restrict river-floodplain commu-
<br />nication and spring peak flmvs are reduced
<br />because of storage in Flaming Gorge Reser-
<br />voir (Muth et al. 2000, Modde et aI. 2001).
<br />An additional factor that may limit survival
<br />of razorback sucker is syrnpatric nonnative
<br />fishes that prey upon or compete with early life
<br />stages of razorback sucker. Over 60 fishes have
<br />been introduced into lotic and lentic habitat in
<br />the Colorado River Basin, and even rnacroin-
<br />vertebrates and small-bodied fishes such as
<br />fathead minnow (Pi:mephales promelas) ~md red
<br />shiner (Cyprinella lutrensis; maximum total
<br />length about 75 mm), "vhich are abundant in
<br />low-velocity nursery areas, are capable of
<br />preying upon razorback sucker larvae (Carlson
<br />and Muth 1989, Ruppert et al. 1993, Horn et
<br />aI. 1994, Valdez and Muth 2005, Olden et aI.
<br />2006, Markle and Dunsmoor 2007). Fast
<br />growth of early life stages of razorback sucker
<br />
<br />lLarval Fish Laboratory, Department of .Fisll, 'Wildlife, and Conservation Biology, Colorado State University, Fbrt Collins, CO 80523. E-maiL kbestgen
<br />@,,"'amercnr.colostate.edu
<br />
<br />15
<br />
<br />4 5lo)
<br />
|