7831

• UCREFRP Catalog Number: 7831
• Author: Dowling, T. E., et al.
• Title: Mitochondrial DNA Variability in the Endangered Razorback Sucker ‎(
• USFW Year: 1996
• Copyright Material: YES

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f)oWling et aI.

mtDNA Diversity in Razorback Sucker

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dellago reintroducd6n con, una vez que las mismas alcancen una talla con alta superoivenda. La ultima
'Ppci6n es la preferlble y deberia ser puesta en efecto como la opd6n mas efidente para preseroar la diver-
'stdaiJ genetica en Xyrauchen texanus.
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Introduction
I

Many freshwater fishes native to the North American
West are threatened with extinction, largely because of
'human influences (Minckley & Deacon 1991). Water-
imanagement practices have reduced and extensively
'modified aquatic habitats and their surrounding land-
.f
, scapes, and nonnative species, mostly introduced as sport
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\ or baitfish, have seriously affected indigenous species
; through competition, predation, and hybridization. More
than 20 native taxa have become extinct in the past cen-
t tory (Minckley & Douglas 1991).
I The plight of the razorback sucker (Xyrauchen texa-
.~ nus) typifies that of many western big-river fishes
1 (Minckley et al. 1991). Historically, this large catostomid
; was widespread and abundant throughout major rivers
! of the Colorado River basin, to which it is endemic. Ra-
I zorback sucker populations seemingly exploded in size
! in newly constructed reservoirs in the lower Colorado
~ River basin, but recruitment was short-lived. In three in-
I stances strong initial year class(es) failed to reproduce
t successfully, and populations persisted ::t 40 years, then
! essentially disappeared (Minckley 1983). Various human
. impacts have combined to extirpate the species, and re-
. cruitment failure now seems prevalent in streams and
reservoirs throughout the species' range (Lanigan &
Tyus 1989; Minckley et al. 1991; u.s. Fish & Wildlife Ser-
vice [USFWS] 1991).
The largest remaining populations are in the upper
Green River, Colorado-Utah (estimated by Lanigan &
Tyus [1989] at fewer than 1000 adults), and Lake Mo-
have, Arizona-Nevada (fewer than 23,300 adults in 1993
[Marsh 1994]). Natural populations comprised of scat-
tered individuals elsewhere are too small to obtain reli-
able size estimates (McAda & Wydoski 1980; Minckley
1983; Lanigan & Tyus 1989; Marsh & Minckley 1989).
Despite more than a decade of active management (re-
viewed in Minckley et al. 1991), its status remained pre-
Carious, and the razorback sucker was listed federally in
1991 as endangered (USFWS 1991).
Although razorback suckers continue to spawn and
produce larvae in both large rivers and reservoirs (Marsh
& Langhorst 1988; Marsh & Minckley 1989; Marsh & Pa-
poulias 1989); all populations are otherwise comprised
only of adults thought to average 25 to more than 40
years of age. Juveniles are virtually unknown, and re-
Cruitment to spawning stocks is undetected. In response
to lack of successful natural recruitment in razorback
suckers and other western fishes, existing hatcheries

were pressed into service to assist in their conservation
(Rinne et al. 1986; Johnson & Jensen 1991).
Concerns for threatened and endangered fishes con-
trast sharply with those for fishes under more traditional
propagation. Sport and commercial fishes are in high de-
mand; therefore, many hatchery stocks of common but
highly-prized species have existed for some time. Rapid
growth, high survivorship, and ease of culture were se-
lected to maximize production, as were other enhance-
ments of the product's desirability, such as body size,
"fighting" qualities, beauty (color), and even palatability.
Propagation programs were designed to meet quotas
that satisified demand in cost-effective ways, with little
regard for anything other than the health of broodstock
or progeny to ensure consistent production. In contrast,
the goal of captive breeding programs for imperiled taxa
is to maintain genetic diversity without adaptation to
captivity. Consideration of genetic features (such as
population structure' and effective population size) is
therefore critical if reintroduced fish are to retain their
ability to respond to changing environments in the wild
(Templeton 1990; Echelle 1991; Hedrick & Miller 1992).
Thus, the institutional goals of hatcheries assigned to
handle endangered taxa were abruptly changed. Instead
of efficient production of large quantities of fish, hatch-
ery managers became custodians of an irreplacable re-
source temporarily removed from nature. We collected
mitochondrial DNA (mtDNA) restriction-site data from
the razorback sucker, the analysis of which revealed an
example of some problems arising from mixing a pro-
duction philosophy for fishes destined for harvest with
the conservation philosophy essential for management
of endangered species.
Mitochondrial DNA has been a useful marker for stud-
ies of population structure (Avise et al. 1987; Avise 1992)
and estimates of genetic diversity (Avise et al. 1988;
1989). It is maternally inherited (Dawid & Blackler 1972;
Avise & Lansman 1983; but for exceptions see Satta et al.
1988; Kondo et al. 1990; Hoeh et al. 1991; Gyllensten et
al. 1991) and evolves rapidly in many vertebrates (Moritz
et al. 1987; see Avise et al. 1992), making it a highly
polymorphic character for tracing maternal lineages.
Razorback suckers have been cultured since 1981 at
Dexter National Fish Hatchery and Technology Center
(DNFH; Johnson 1985; Johnson & Jensen 1991). We
contrast mtDNA diversity in hatchery-produced stocks
with those of the source population in Lake Mohave to
evaluate success in maintaining genetic variability. Re-
duction in the mtDNA diversity of a hatchery stock rela-

Conservation Biology
Volume 10. No. I, February 1996

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