Table Of ContentGu^ResearchReports,VoL8.No.4.387-394,1991 MuuiscriptleceivedMarch12,1991;acceptedApril8,1991.
LONG-TERMADULTPOPULATION FLUCTUATIONS
AND DISTRIBUTION OFTHE SPOT, LEIOSTOMUSXANTHURVS,
IN MISSISSIPPI
BRUND.LEBLANC*^,DEBORAHL.MURPHY’,
ROBINM.OVERSTREET’,ANDMICHAELJ.MACEINA’
^Presentaddress: LouisianaStateUrtiversUyAgriculturalCenter!LouisianaCooperative
ExtensionService,8201 W.JudgePerezDrive,Chalmette,Louisiana 70043
CoastResearchLaboratory,P,0.Box7000,OceanSprings,Mississippi 39564
^DepartmentofFisheriesandAlliedAquaculture,AuburnUniversity,Alabama 36849
ABSTRACT AdultspecimensofthespoULeiostomusxanthurus,werecollectedfrombayou.MississippiSound,andbarrier
islandlocationaelon^theGulfCoastofMississippifromNovember 1982toJuly 1989. Themeantotallengthofallspot
sampledincomparablegillnetsetswas219mm(±14standarddeviation,n=4,338). Ninety-livepercentofthespotwere
collectedintheislandandsoundareas,wherethesalinitywashigherthaninthebayous. Catchperuniteffortwashighat
islandandsoundatatioosinspringandautumn,withrelativelyfewRshcaughtduringthewinterspawningseasonandsummer.
Therelativelyhighfrequencyofspotobservedattheislandstationsintheautumnwasprobablyinfluencedbyspawning
migrations,andthehighspringvaluesmayrepresentacombinationoftwoabundantyearclasses. Thetwogreatestyearly
collections, in1983and1986,mayhavebeeninfluencedbysamplingconditionsorbyenvironmentalconditionsfavorable
tosurvivaleitherduringthoseyearsorearlierwhenthosefxshwerepostlarvac. Thesmallestyearlycatchoccurredin1985
andmayhavereflectedthehanhweatherconditionsthatyear.
iNTRODUenON waterdepth of0.5 to 3,0-m onehourbefore sunsetand
retrievedfourhourslater.
Thespot,Leiosiomusxanthurus, isacommon fish in Spotwerereturnedtothelaboratorywheretotallength
estuaries along the Gulf Coastof Mississippi. Several (TL)andstandardlength(SL)weremeasuredtothenearest
studieson thelifehistoryofthis specieshavebeencon- millimeter. Representative samples were examined to
ducted(e.g.,Pearson1929;HildebTandandSchroder1928; determine the state of sexual maturity using methods
HildebrandandCable 1930;Dawson 1958;Parker 1971). similartothoseestablishedbyOverstreet(1983).Thedate,
Limitedinformationisavailableonlong-termpopulation watertemperature,salinity,turbidity,cloudcover,andsea
fluctuations. KobylinskiandSheridan (1979) examined conditionswererecordedpriortoeachnetset. Watertem-
thelong-termseasonaldistributionandabundanceofspot peraturewasmeasuredtothenearestPCwithahand-held
inApalachicola Bay,Florida, andJoseph(1972) studied ihennomeler. Salinitywasmeasuredtothenearest 1 ppt
populalion trends along the mid-Atlantic Coast Long- withalemperamre-compensatedrefractometerorconduc-
termmonitoringofadultspotmayindicatefluctuationsin tivitymeter,andturbiditywasmeasuredwithasecchidisk
populationsinfluencedbynaturalchangesintheenviron- tothenearestcm. Mostwatertemperaturesandsalinities
ment. The objectivesofthis study were toexaminethe weretakenwithin 10cmofthesurface.
seasonalandannualvariationincatchralesoflargerspotat Threehabitattypes,representedbyatotalofsixloca-
island,sound,andbayouhabitatsinMississippiinrelation tions,weresampledfromthestudyarea(Figure1). Bayou
totemperature,salinity,andreproductiveinfluences. stations were located adjacent to Biloxi Bay near Fort
Bayou and Popps Ferry bridges. Sound stations were
MaterialsanpMethods locatedoffthenorthcentralportionofDeerIslandandthe
northwest portionofRoundIsland. Islandstationswere
Spot samples and hydrological data were collected locatedonthenorthcentralareasofHornandShipIslands.
monthly from November 1982 throughJuly 1989 ai six A one-way analysis-of-variance test (ANOVA) was
stationsalongtheMississippiGulfCoast(Figure1). Speci- usedtodetectsignificantdifferencesbetweenmeanvalues.
mens were collected with 183-m long by 2.4-m deep In cases where differences were detected, means were
monofilamentgillnets* Thenetswerecomprisedoffour comparedusingTukey’smultiplerangetest(Tukey1953).
45J-mpanelswith7.0,9.5,152,and20.3-cmstretchmesh Mean catch values in Figures 2 and 3 are presented as
that were anached together. The net was set on the arithmeticmeans. Thevariancewasproportionaltomean
substratum perpendicular to the shore with the smallest values,henceIog,Qirajisformationsofdatawereperformed
meshpanelabuttedtoorneartheshoreline. Itwassetina priortousingtheANOVAandmultiplerangetests.
387
1
388 LeB1j\NCetal.
Linearregressionwasperfonned tocomparetherela- Dbcxission
tionshipbetweenTLandSLinnonhemGulfofMexico
spot to thatcalculated by Dawson in 1958 using South Townsend(1956)examinedtheage-lengthrelationship
Carolinaspot. Spotmeasuredbythesamebioiechnician ofspotinFloridausingscalesandlength-frequencies,and
werecompiledfromalargerdatabaseconsistingofspotwe he^terminedthatspot between 150-185 mm SL (TL=
collectedinthesamegeograj^calareaasthedatausedfor 187-230mmusing theequation TL=1.233[SL] +2from
other statistical analyses perfoamed in this study. The Dawson[1958])werepriiWilyage-2fish, Parker(1971)
regressionequationwascalculatedusingthemeanTI.for determinedthatspott^enfromtheGulfofMexicogrew
a given SL to compare to Dawson's (1958) equation approximately11mmpermonthduringtheirfirstyearand
calculatedfrommeansof5mmclassintervals. 5,5mmpermonthduringtheirsecondyear.Consequently,
these dka would suggest that 220 mm TL fish were
approximately2.5yearsold. Ourdataindicated79%ofthe
Results spotcapturedwerebetween190and229mmTLandwere
probably2yearsold. Althoughourdatarepresentlength-
Gill nets selected larger spot; 96% ofthespecimens frequencydistributionskewedtowardlargerspot(190-33
caughtweregreaterthan200mmTL(Table1).Meshsizes mmTL),pre.sumablyinthe2-and3-yearageclasses,we
of7.0,9.5, 15.2,and20.3cmcaptured95.3,4.4,0.2,and rarely observedindividual spotlarger than250mm TL.
0.1% ofthe spot, respectively, from the combination of Only66outof4,330(1.5%)spotcaughtbygillnetwere
bayou, sound, and island stations. Mean size of spot largerthan255mm. Gunter(1950)similarlynotedonly
captured did not vary significantly among the bayou, 2%of1,246spotlongerthan255mmTLc^turcdbytrawl
sound,andislandstations: 219mm±16 (n=224),221mm along the Gulf Coast. Southeast Area Monitoring and
±16(n=l,382),and219mm± 12(n=2,732),respectively. AssessmentProgram(SEAMAP)datafrom1982-1989on
The linearregressionbetweenTLandSL calculatedfor spot captured from stations in Gulf ofMexico offshore
specimens from the northern Gulfof Mexico spot was watersboundedby29°10'to30'*10’Nlatitudeand87°30'to
TL=1.135[SL]+ 14,2,r2=0.994. 89°00*W longitude indicated only 1% ofthe 1395 spot
Monthlymeancatchratesofadultspotvaried among measuredwerelargerthan255mm(personalcommunica-
bayou, sound, and island stations (Figure 2). A high tion,KennethSavastano,NationalMarineFisheriesServ-
percentage(63%)ofthetotalcatchoccurredinthehigh-to- ice, NSTL. MS 39529 SEAMAP 1991). In addition,
moderate salinities of the island stations, whereas 32% Dawson(1958)summarizedcatchdataofspotcollectedby
occurred inthemoderate-salinities ofthe soundand 5% trawlersofftheAtlanticCoast(HildebrandandSchroder
ocemredinthelower-salinitiesofthebayou. Temperature 1928; Hildebrand and Cable 1930) and reported 10 of
andsalinityvariedamonglocationsandseasons(Table2), 27,227(0.04%)^255mmTL. OurdatafromUieMissis-
and correlationanalysis indicateda weakbutsignificant sippigillnetstudyandthoseby othersmentionedabove
relationshipbetweensalinityandthenumberofspotcaught demonstratetheinfrequencyoflargespotinbothestuarine
(p= 0.20, Table 3). A bimodal frequency ofcatch was andoffshoreareas,suggestinglowsurvivalofspotbeyond
evidentbecauserelativelylargenumbersofadultspotwere 3 yearsofage.
collected ai theislandandsoundstatiemsinMarch-April OurHVSLregression equation wasnotusedbecause
andinOctober(Figure2). Numbersofspotcapturedfrom wedidnothaveagedatacorrespondingtothatofDawson
thebayousiadonswererelativelylowduringeachmonth (1958), OurregressionequationsandthoseofDawsonare
throughoutthestudyperiod. Althoughmeancatchvalues more similar for smaller spot than larger ones and are
among years were not significantly (p > 0.05) different probablynotsignificantlydifferentfromeachotherinthe
withineachstation,thetotalcatchvaluesfromislandand 150-185mm SL range. However, the lengths differby
sound stations exhibited considerable annual variation, morethan 10mmforfishgreaterthan220mmSL.
withespeciallylargecatchesoccurringin 1983and 1986 Monthlyvariationincatchcouldhavebeeninfluenced
(Figure3). bymigration,byshort-termandlong-termenvironmental
Examinationofspotgonadstakenhrorabayou,sound, variations,byspawningperiods,andbysampling.Dawson
andislandstationsdemonstratedthatgravidfemalesand (1958) noted the number of spot ^ 150 mm TL in his
ripemalesoccurredinallthreehabitats(Figure4).Mostof samplesfromSouthCarolinawasgreaterinMarchthanin
theseindividualswereobservedfromtheislandandsound latespring. Thoserelatively small catchesinlate spring
stationsinOctoberandNovember. Alownumberofripe persisteduntil the startofautumn when the numberin-
malesandgravidfemales,however,werecollectedfrom creased(Dawson1958). Asimilartrendwasalsoobserved
thebayoufromOctobertoDecember. inourstudy foradultssampledfromtheislandandsound
PopulationFluctuationsandDettubutionofAdultSpot 389
Figure1.LocationsofthesixsamplingareasinMississippi: PoppsFerr FortBayou,l>eerIsland,RoundIsland,ShipIsland,
andHornIsland.
stationsinMississippi HildebrandandCable(1930)noted months in 1983, 1984, and 1986. C!olIections made in
acomparabletrendforjuvenilespotfromnearBeaufort, Marchof1983 and 1986accountedfor67%ofthe total
NorthCarolina.Thelargenumberofadultswecollectedin seven-yearcatchforMarch,and57%ofthetotalnumber
October(Figure2)mayhaveresultedinpartfiromamigra- forAprilwascaughtin1983and1984, Areviewofsalinity
tionofthefishfrominshoreandcoastalhabitatstooffshore andtemperaturedatawecollectedeachweekduringanda
spawning areas. Several studieshavereportedspawning fewmonthsprecedingthepeakcollectionperiodsrevealed
migrationsOfspotduringautumnbasedonlargecatchesof novariationsinconditionsthatwouldreadilyexplainwhy
adultsfromoffshorespawninggroundsrelativetosimulta- theaboveperiodsweremoreproductivethanintermediate
neous smallcatchesfrom inshoreareas (Hildebrand and periods. Samples ofanon-dispersed population during
Schroder1928;Pearson 1929;Gunter1938,1945;Dawson differentconditionsofwaterandairprobablycontributed
1958). Wecorroboratethatconclusionwithsimilarobser- tosomeofthevariation. Pertiapsfavorableenvironmental
vations(Figure2). conditionsexistedwhenthesefishwerelarvaeandposUar-
Large numbers ofmigrating spot collected from the vae,contributingtothedevelopmentofstrongyearclasses.
sound and island stations during late autumn had fully IfdataforthemonthsofMarch1983and 1986andApril
developedgonads. AsexpectedfromearUerreports(Gunter 1983and1984wweremovedfiromthetotaldata,thetotal
1938,1945;Dawson1958),fewspotwerecollectedduring numberofoccurrencesforthemonthsofMarchandApril
Dccember-February. Largermeancatchesofspotfromthe wouldnotbesignificantlydifferent(p>0.05)fromthoseof
islandstationsinMarch(mean=75)andApril(mean=75) May-September, Thedataindicatelong-termstabilityof
may have been influenced by the spent (spawned) or thespotpopulationfromMarchtoSeptemberduringthe
developingadultsmovingintoandoutofthearea. These years 1983to 1988.
movementsmayhavebeentriggeredbygradualincreases Annualvariationinthespotpopulationis typicalofa
inwatertemperatureinconjunctionwithconsistentmoder- fishwitharelativelyshortlifecycle(Joseph1972). Joseph
ate-to-highsalinities thatoccurred during thosemonths. alsostatedthatpopulationfluctuationscouldbeinfluenced
Therelativelyhighnumberofspotobservedfortheseven- bysurvivalofearlystages,possiblyresultingfromenviron-
yearperiodattheislandstationsduringMarchandApril mentalconditionsthatprevailedonthespawninggrounds.
were influenced by especially high catch rates in those However,detrimental conditions inthenurserygrounds.
390 LeBlancetal.
TABLE
1
mm
Totallength-frequencydistributionin10 incrementsofallspecimensofLeiostomusxanihurusmeasured
fh)mMississippi waters on a monthly basis from November 1982 to July 1989
TL (mm) Jan Feb Mar Apr May Jun Jul Aug Sep . Oct Nov Dec Totals
120-129 2 2
130-139 1 1 2
140-149 1 1 2
150-159 1 1 2
160-169 1 1 1 3
170-179 1 2 1 1 5
180-189 1 3 2 3 2 2 2 15
190-199 1 2 5 29 9 19 25 16 15 22 9 5 157
200-209 9 15 42 160 65 51 61 60 53 129 35 9 689
210-219 25 12 160 270 104 100 97 105 87 281 85 37 1,363
220-229 23 35 264 230 64 71 55 65 37 251 97 23 1,215
230-239 20 23 147 120 25 24 12 10 18 100 70 7 576
240-249 8 6 58 28 6 7 1 1 3 48 30 3 199
250-259 1 1 14 3 2 1 1 7 29 1 60
260-269 3 1 1 3 18 26
270-279 1 1 5 7
280-289 3 1 4
290-299
1 1
300-309
310-319
320-329
1 1
330-339
1 1
>
PopulationFluctuattonsandDisTWBunoNofAdultSpot 391
CCS
1989 s 2 cn C s c
'w'
+1 +1 +1 Tl +t +1 Vi +1 +1 +1 +l
July <s s a
cs ?}
to
19S2
g s s s 5 S 5 S @ s
+1 +1 +1 +1 +1 +1 +1 +1 Tl +1 +1 +1
November ?5 a a R cCSn ccsn Si cr-s*
—
months
c s s c S s s s s c
by +1 +1 +1 Ti +1 +1 +! o+1 +1 +1 +1 +1 +1
t CJ ^2 s s cs cn OCnS ?S clso s VO
(l\
stations
CQO So 6 § s oo $ s 6 s $
'w'
island +1 +1 +1 +1 +1 Vi +1 +1 +1 +1 Vi +1 +1
C'cOS ON VO VO »n ^2 VO r- cCsO a
and
sound,
s s s s s V— s s
bayou, +1 Vi +1 +1 +1 +l +1 +1 +1
of <s <r> i2 s ?3 a ?5 a
^C)
temperature z} +1 +1 +1 +1 m+1 +1 +1 +1 +1 +• +1
cn VO NO tri
and
(ppt)
deviation
saJinity
^Standard
Mean
392 LeBlancetal.
collected
spot
of
number
Mean
JaB Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
f
^ 2. MeannumberofadultspotbymonthfromthreesamplinglocationsfromNovember1982through
>89. The letter Indicatesasignificantdifference (p >0.05).
collected
spot
of
number
Mean
1983 1984 1985 1986 1987 1988
Year
Figure 3. Meannumberofadultspot byyear fbom three samplinglocations from 1983 through 1988.
. .
394 LeBlancetal.
TABLE3
Correlation matrixforsalinity,temperature, localily, and numberofspotcollected
No. fish
Salinity Temperature Location collected
Salinity -0.07 0.74* OiO*
Temperature 0,003 0.03
Locality 0.32*
NumberofCases 492
*1-tailedsigmficance .001
such asextendedperiods oflow temperature*couldalso spotin 1987and 1988mayalsohavebeeninfluencedby
affectsurvivalandmigrationofyoung spotintothebays those sameharshconditionsadverselyeffecting the sur-
duringspring,subsequentlyeffectingthestrengthofthose vivaloflarvaeoryoung-of-the-yearfishduringthewinter
yearclasses.Forexample,ourcollectionofwedclyweather of1985.
data indicated that in January 1985, water temperature
plungedfromameanof10.3Xtoalowof2.5®Cforatleast Acknowledgments
48hours*withiceforminginmanybayous. Alsoduring
thatyear,threehurricanesmovedthroughthearea. Those We thankRonniePalmer, HelenGill, Randy Pierce,
extremeweatherconditionspossiblydispersedormoved NateJordan,Pat Murphy.GeorgeCantreU, StuartHarri-
manyadults intooffshorewatersin 1985 andnegatively son,andWaltBrehmfiromGCl^whoaidedindifferent
influencedsurvivalofyoungfishinthebayousandsound. aspects of this study. Others also assisted at different
Thelowertotalcatchofadult spotseenin 1985 may be periods. Thestudywasconductedincooperationwiththe
related to theharshweatherconditions occurring inthat U.S.DepartmentofCommerce,NOAA,National Marine
year. Moreover,therelativelylownumbersoflarger,adult FisheriesService,GrantNo.NA90AA-D-IJ217.
LiT^tATURECited
Dawson,C.E. 1958. Asurveyofthebiologyandlifehisloiyof Joseph,RB. 1972.Thestatusofthcsciaenidslocksofthcmiddlc
the spot,Leiostomusxanthurus^with specialreferenceto AtlanticCoast. ChesapeakeScience13:87-100.
SouthCarolina, ConlribidionsfromBears Laboratory Kobylinski, G. J. and P. F. Sheridan. 1979. Distribution,
28:M8. abundance, feeding and long-tcnn fluctuations of spot,
Gunter,G. 1938. Seasonalvariationsintheabundanceofcertain Leiostomusxanihurus,andcioakjci^Micropogoniasundula-
estuarine and marine fishesin Louisiana, with parU'cular tus, in ApalachicolaBay,Rorida, 1972-1977. Contribu-
referencetolifehistories. EcologicalMonographs8:313- tionsinMarineScience22:149-161
346. Overstreet,R.M. 1983. Aspectsofthebiologyofthespotted
Guntcr.G. 1945.StudiesonmarinefishesofTexas.PuW/cor/o/u seatrout, Cynoscion nebulosus, inMississippi. Gu^Re-
oftheInstituteofMarineScience,UniversityofTexas1:9- searchReports,Supplement 1:1-43.
190, Parker, J, C. 1971, The biology of the spot, Leiostomus
Gunter,G. 1950. Correlationbetweentemperatureofwaterand xanthurus, and thecroaker, Micropogoniasundulatus, in
sizeofmarinefishesontheAtlanticandGolfCoastofthe twoGulfnurseryareas. TexasA&MSeaGrantPublication
UnitedStates. Copeia1950(4):298-304, NumberTAMU-SG-71-210,182pp.
Hildebrand,S.F. and L. Cable. 1930. Developmentand life Pearson,J.C. 1929. Naturalhistoryandconservationofthered
history of fourteen telcostoan fishes at Beaufort, North fish and othercommercialsciacnidson theTexas coast.
Carolina. BulletinoftheUnitedStatesBureauofFisheries BulletinoftheUnitedStatesBureauofFisheries44:29-214
46:383-488, Townsend,B.C.1956.Astudyofthespot,L«/o,r/£>/7tusxnn//iw-u;r
Hildebrand,S.F.andW.C.Schroder. 1928. FishesofChesap- Lacqjcdc,inAIligaiorHarhor,Florida.M,S.Thcsis,Ocean-
eakeBay. BulletinoftheUnitedStatesBureauofFisheries ographyInstitute,RoridaStateUniversity.43pp.
43:1-366. Tukey,J.W, 1953.Thcproblemofmultiplccomparisons.Ditto,
PrincetonUniversity,Princeton,NewJersey.
