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<br />126
<br />
<br />mtDNA Diversity in Razorback Sucker
<br />
<br />straining adults to spawn naturally in protected, isolated
<br />bays where larvae can survive and grow to suitable size
<br />in a predator-free environment (Marsh & Langhorst
<br />1988; Minckley et aI. 1991); the other involves capture
<br />and transfer of reservoir-spawned larvae into protected
<br />bays (Marsh, unpublished data). Although natural spawn-
<br />ing of adults in protected backwaters will yield fewer
<br />fish per year than hatchery production, continuation of
<br />such a program for several years using different adults
<br />each year would allow for maintenance of higher levels
<br />of genetic variability. Even fewer total progeny per year
<br />are available by collecting wild-spawned larvae and rear-
<br />ing them in protected sites, yet this method will almost
<br />certainly preserve the most variability.
<br />We strongly recommend the last option be empha-
<br />sized and advise that such a program, already initiated,
<br />be pursued in earnest. We fear, however, that hesitation
<br />or intransigence may preclude the direct capture and
<br />husbandry of wild larvae in numbers that can assure
<br />maintenance of genetic variation. When the old, wild in-
<br />dividuals begin to die, which will be soon, it may be too
<br />late; there is strong evidence that the population is al-
<br />ready in precipitous decline (Marsh 1994). We advise
<br />even more strongly to resist the temptation to use
<br />known and established methods, such as hatchery cul-
<br />ture, to quickly produce large quantities of individuals to
<br />replace the existing Lake Mohave stock. Population size
<br />can clearly be maintained through stocking hatchery-cul-
<br />tured fish but at a substantial cost to innate genetic vari-
<br />ability and with unknown future results.
<br />On the other hand, we do not advocate an end to the
<br />hatchery program because it is imperative that a large,
<br />diverse broodstock be maintained in case other efforts
<br />fail. The present broodstock at DNFH should be re-
<br />placed with wild-caught individuals, however, and pro-
<br />duction should be designed to maintain documented ge-
<br />netic variability in offspring. produced for any future
<br />purpose. Progeny of the current broodstock should not
<br />be released to replace the existing Lake Mohave popula-
<br />tion. The bay-culture program should also be continued
<br />and expanded, if for no other reason than to provide ad-
<br />ditional habitat where both bay-culture and wild-caught
<br />larvae can grow. Rearing should be geographically as
<br />near Lake Mohave as possible to minimize expense and
<br />fish losses through handling. The safest course would be
<br />to keep all three options open, if economics allow and if
<br />dedication and mandate are sufficient incentives, so that
<br />if one method fails the others may be attempted.
<br />
<br />Acknowledgments
<br />
<br />We thank M. E. Douglas, B. L. Jensen, S. Johnson, D. D.
<br />Oakey, B. Williams, J. H. Williamson, and innumerable
<br />other colleagues and students for assistance in collecting
<br />or providing specimens; B. L. Jensen for hatchery records;
<br />
<br />Conservation Biology
<br />Volume 10, No.1, February 1996
<br />
<br />DoU'li ng et aI.
<br />
<br />M. E. Douglas and D. D. Oakey for technical assistance;
<br />B. D. DeMarais, A. A. Echelle, and P. W. Hedrick for dis-
<br />cussion and critical review of the manuscript. Federally
<br />and state-listed species were obtained under appropriate
<br />permits, those from Arizona under Federal Endangered
<br />Species subpermit number PRT-676811. This work Was
<br />supported by Cooperative Agreement O-FC-40-09530
<br />(to T. E. Dowling and W. L. Minckley) from the U. S. Bu-
<br />reau of Reclamation and the U. S. Fish and Wildlife Ser-
<br />vice (to P. C. Marsh and W. L. Hinckley).
<br />
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