Bay drainages. No differences inmtDNAhaplo- tweenpopulations ofA. transmontanusfrom the
types weredetected insturgeonfromdifferentloca- Fraser andColumbiarivers (Brown et al.1992,
tions in the St.Lawrence River; however, haplotyp- 1993). In themostrecentglacialadvance, the lower
ic frequenciesdifferedfromthose in theWaswanipi ColumbiaRiver wasbelieved t oremain an ice-free
River in the James Baybasin. The lowermtDNA refugium, whereas theFraserRiver was completely
heterogeneity infishfrom the St. LawrenceRiver glaciated.Sequencevariation of thecontrolregion
was interpreted toreflectgreater anthropogenic in- was consistentwith thehypothesisthat theColum-
fluences onpopulationabundance. bia River was thefoundersource for theFraser Riv-
Ferguson et al. (1993, 1997 thisvolume) used population(Brown et al.1993).However,levels
RFLPanalysis ofmtDNA anddirect sequencing of of overallmtDNAdiversityweresignificantly high-
the controlregion ofmtDNA toinvestigatestock eramongfishfrom theFraser River than the Co-
structure ofA. fulevscensfrom Canadiansystems, lumbiaRiver,despite thegreaterrecency of the
with anemphasis on theMoose Riverbasin in On- FraserRiver population (Brown et al.1992). It was
tario. Little differentiation ofmtDNAhaplotypes hypothesizedthatlowergeneticdiversity in the Co-
was found among majortributaries of theMoose lumbiaRiver population resulted fromreduced ac-
River basin, suggesting an absence of discrete cess tohistoricspawningareas due to theconstruc-
stocks.However,sturgeonfrom theMoose River tion ofdams.Brown et al.(1992)also found signif-
basin exhibited significantly higher levels of icantdifferences inmtDNAhaplotype frequencies
mtDNAdiversity andweregeneticallydifferentiat- betweensamples from theFraserRiver andColum-
ed fromfishfrom theGreatLakes-St. Lawrence biaRiver,indicatingthatthese tworiverssupport
drainage andotherHudson Bay-James Baypopula- genetically distinctpopulations ofsturgeon. Be-
tions.Theseworkers hypothesizedthatmtDNA cause haplotypedifferences were notfixedbetween
differentiation insturgeon from Canadianwaters the two populations, theauthorssuggestedthat low
resultedfrompost-Pleistocene colonization from levels ofgeneflowbetweensystems may beoccur-
separaterefugia in theMississippi and St.Lawrence ring. Alternatively, wesuggestthatgiven thebrief
River drainages.Furtherinvestigation ofmtDNA timesincedivergence of these populations, the ac-
diversity inextantstocks ofA. fulvescensin eastern cumulation ofsignificantdifferences ingenotype
and western U.S. drainages should resolve this frequencies indicateseffectivereproductiveisola-
question. tion ofthesesystems.
Acipenserstellatusis an abundantsturgeon spe- Populations ofA.oxyrinchusoccur in drainages
cies in theCaspianSea.Stockstructure ofthis spe- of the Gulf of Mexico andalong theAtlanticcoast
cies in thesouthern portion of theCaspian Sea was ofNorth America.Acipenseroxyrinchusdesotoi
investigated byrestrictionenzyme digestion of the (Gulfsturgeon) areconsideredthreatened by the
PCR amplifiedND5/ND6region ofmtDNA. Al- U.S.Fish andWildlifeService. Historically,A. o.
though polymorphic haplotypes were identified, no desotoiwere found inmajorriversystems extend-
significant differences in haplotype frequencies ingfromcentralFlorida to theMississippiRiver;
were detectedamongfish fromfourregions.which many ofthese drainagesstillhostdepleted popula-
led to the conclusionthatA. stellatusin the southern tions(USFWS and GSMFC^6 ). Efforts arebeing
Caspian Seaprobably represent asingle stock (M. considered to restore depressed populations
Pourkazemipersonalcommunication). through hatchery supplementation. However,
Acipensertransmontanusoccurs fromCalifornia knowledge of thestockcomposition ofA. o. desotoi
to Alaskawithviablefisheriescurrentlycentered in wasfederallymandatedprior to the initiation of re-
the ColumbiaRiver,Washington and theFraser storative efforts, sothatnative g e mpools are pre-
River,BritishColumbia. Both sequencing of the
rapidly evolving control region ofmtDNA and (^6) U.S. Fish and Wildlife Service and Gulf States Marine Fisheries
Commission.1995.Gulfsturgeonrecoveryplan.Atlanta, Geor-
gia. 170 pp.
RFLP analyses of the entire mtDNA molecule were
used to examine theextent ofdifferentiation be-