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166
<br />R ?1)1
<br />sucker larvae have failed to produce quantitative
<br />data, and thus could only speculate on importance
<br />of predation as a cause of mortality, A major prob-
<br />lem has been detection of prey items in stomachs of
<br />fishes that masticate or otherwise render foods vi-
<br />?y? 'sually unrecognizable, or after digestion has pro-
<br />ceeded for periods of more than a few hours (un-
<br />publ. data). These difficulties must be resolved if
<br />the role of predation is to be determined. The
<br />former may be overcome by use of serological tech-
<br />niques (Boreham & Ohiagu 1978, Engvall & Perl-
<br />mann 1972, Heusser et al. 1981, Monroe 1985), but
<br />even these methods may be time-limited by rapid
<br />prey digestion (Theilacker et al. 1986) and thus
<br />require close-order sampling.
<br />Investigations to confirm fate of larval razorback
<br />sucker in Lake Mohave have yet to be conducted,
<br />but may be critical to management and recovery of
<br />the species. If, for example, it were determined
<br />that a significant reduction in predation pressure
<br />on wild or reintroduced stocks would allow
<br />establishment of self-perpetuating populations of
<br />the native, then management activities might be
<br />directed toward reduction of established popula-
<br />tions of known predators. Ichthyocide reclamation
<br />to remove catfishes from selected Arizona streams
<br />and subsequent stocking of razorback suckers is an
<br />example of how this management might be imple-
<br />mented. Such an experiment may be necessary to
<br />resolve the elusive question of why stocked juve-
<br />nile razorback suckers have apparently realized
<br />limited survival (Marsh 1987, unpubl. data) and, at
<br />least circumstantially, would contribute toward ex-
<br />plaining lack of recruitment in Lake Mohave and
<br />elsewhere
<br />The alternative of planting razorback suckers at
<br />a stzeL e'EativeIy unmune to 'redation may succeed
<br />in reestabhs ing it stocks, but still fail to msure
<br />self peipeiuation if predation on larvae` prevents'
<br />recruitment. nfortu -ately, reclamation is proba-
<br />bly infeasible other than in local areas of reservoirs
<br />and remaining mainstream habitat of the Colorado
<br />River that comprise much of the original range of
<br />the species. Eventual recovery of razorback sucker
<br />and other imperiled big-river fishes of the South-
<br />west may best be achieved in backwaters, oxbows,
<br />and smaller tributary habitats amenable to substan-
<br />tial, perhaps repeated, removal of non-native
<br />fishes.
<br />Acknowledgements
<br />This work was funded in part by contracts to Ari-
<br />zona State University from U.S. Fish and Wildlife
<br />Service Region II, Office of Endangered Species,
<br />Albuquerque, New Mexico; U.S. Bureau of Recla-
<br />mation, Lower Colorado Regional Office, Boulder
<br />City, Nevada; and Arizona Game and Fish Depart-
<br />ment (AZGFD), Phoenix. Permits were issued by
<br />U.S. National Park Service, Nevada Department
<br />of Wildlife, and AZGFD. J. Brooks, T. Burke,
<br />and W.L. Minckley participated in various aspects
<br />of the studv; they and W.R. Courtenay, D.L.
<br />Galat, and D. Papoulias reviewed the manuscript.
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<br />Mohave. Biol. Bull. No. 7, Nevada Department of Wildlife,
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