95

CRAB PREDAT10N ON GREEN TURTLE（CHELONL4MYDAS） EGGSJNCUBATED ON A NATURAL BEACH ANDlN TURTLE HATCHER］ES

AhmadAlilandKamarruddin［brahim2

イ M∂血eF伝わe〟e5尺e50U′℃eSDeve′叩m即加dMan∂9emenf加pa伽1e咄 SoutheastAsianFISheITeSDevelopmentCenteI；21080Chende／Tng，77）Il）nganu，Malaysla． 2 7t／rtIeandMa血eEcosystemCenter（TUMEq，DeparhentofFjsheriesMalaysia，23050 Du〃9Un，福相〃99∂爪ノ，M∂／∂yS胤亡－m∂／／了kdm55＠y∂わ00．COm

ABSTRACT

AstudyofcrabpredEltionongreenturtle（CheIoniamydas）eggswasconductedonanaturalbeachofMak Kepit，PulauRedangandatturtlehatcheriesinGeligaandChendorduringMarch－September2002・Theobjectives WeretOquantifycrabp「edationonturtleeggsonnaturalbeachandhatcheriesandtodeterminetheeffectiveness Ofp［asticmeshfencingforpTeVentingcrabpredation・AtotalDf658nestscompriseofthoseonnaturalbeach（214）， hatcher】es（429）andexperimentalplot（15）wereinvestigated・ResultshovvedthatmoTtalityofgreentur［leeggsin thestudyareaduetoghostcrabpredationisnotanimportantthTeataSthemagnitudeofdepredationwasonlyl・3％ （rangeO．4％－2．7％）．Twospeciesofcrabs，i・e・，Ocypodeceratophtl7aImusandOcypodekuhJliweTereCOrded・The useofO．5cmmeshedplasticnetEontofencesurroundingnestsdowntolmdeepundeTSandsurfacewasproven effectiveinpreventingcrabsfromentenngthenestsintu「tlehatcheries・Thispreventivemethodwasrecommended foradoptionintheoperationofturtlehatcheries，aSitwaseffectiveandeco－friendIysound・

Keywords：ghostcrabpredation，Cheloniamydas．Ocypodespp，naturaIbeach，turtIehatchery

］NTRODUCT10N

The green turt］e，Chelonia mydasis known to Eggsandhatchlingsofseaturtlesaresubjecttoa nestextensivelyonselectedsandybeacheson廿1emainland numberofnon－human predators．There are manyspe－ and offshoreislands of Peninsular Malaysia．Highest Cies ofpredators that prey upon the10ggerhead turtle COnCentrations of nesting green turtles occur on theCarettacaretta．Theireggsandhatchlingswerereported isLandofPulauRedang．foIEowedbyGeEigaandPaka，all to be predated bythe nineLbanded armadillo，Dasypus islocatedinthestateofl七rengganu．lnthestateof novemcintus（Drennen etal．，1989）．Theywerealso Pahang】theonlygood greenturtlerookerylSlocated Preyeduponbyanumberoftheotherpredatorssuchas atChendor，Whereas PantaiSegariofPerakisa main theAtlanticghostcrabs，Ocypode quadrata（Sundn， rookeryforthisspeciesonthewestcoastofPeninsular 2001）．thesurfcrabs，ArenaeuscrIb／笥，（uS（Frick．2003）， Malaysia. There are also nesting of green turtles Varanidlizards，「aCCOOnS．COatis，feraldogs．coyotes， reportedintheotherareasbuttheirnestingnumbersare Shorebirds，Vultures，Wild boars，and ghost crabs considered small（Kamarruddin，1994）．Thisreportalso （Fowler，1979；Mrosovsky，1983；Cornelius，1986； concIuded thatthe nesting season ofgreen turtlesin Connant，1991；Eckert，1992；BbmiresandGuinea．2001）． Peninsular MaEaysia occursthroughouttheyearwith Hatchlingsofgreenturtleswhenenteringseafromrook－ PeaksinJune－JulyperiodL erybeachesandduringtheswimrfrenzyperiodenroute 96 tonurseryhabitatswereeas11yeatenby the grouper，PromjcropsIance10tuS （Witzell，1981）． Theghostcrabs（Ocypodespp） are fast running crustaceans with a SPeed of up to3，4m／sec，CaPable of COVenng［ongdistanceduringforay．This SPeCiesspendsthegreaterparts ofits lifein，Or aSSOCiated with a burrow． Hughes（1966）reported that burrows havedepththatrangefrom30cmtol．3 mdependingonhow10ngtheyhadbeen OCCuPiedandtheirpositiononthewave beach．The burrows were most often rocatedin positions between highwater SPnngtideto）uStberowhighwaterneap tide．Ghost crab coIEectiveEy exhibits manyfeedingtacticsand activitycycles （Hermkind，1983）．Theyleavetheirburrows mostly at night and scurry along the beachinsearchoffood．Althoughghost Crabsspendmostoftheirlivesonland． theystillhavegllEsthattheymustkeep 円9．†M叩5わol〝血9納e／oc8f旧∩50r軌佗eSfu（少S〟eson肋ee∂Sf CO∂SforPe／血SU／∂rんね／∂yS／a－Ma〟Kep／f，Ge旬∂∂ndC／†endor Wetinordertobreathe．Theyperiodically Shedanexoskeletonwhentheyoutgrowit， Ghostcrabdepredationonseaturtleeggs and hatchlingsisfrequentlyobserved． MATERIALSANDMETHODS arthoughtheextentof10SShasnotbeen quantified． Study sites ThreestudysitesontheeastcoastofPeninsu［ar Theinformation aboutdepredationofseaturt［e Malaysiawerechosen（Figurel）．MakKepit，anatural eggsand hatch‖ngs byghostcrabsin Malayslaisvery WhitesandbeachislocatedontheislandofPu［auRedang SCanty．John（1998）duringhisstudyatChagarHutang intheSouth ChinaSea．TwoothersitesareturtIehatch－ OntheislandofPulauRedangdocumentedtwospecies enesatGeligaandChendoronthemainlandwherethe Ofghostcrabs：OcypodeceratophthaImusandOc）pOde beaches areofbrown－tyPe Sand． kuhliiand reported thatghost crabswere the most Quantification ofcrabpredation－Quantification PrOminentnestpredators（56．67％），HearsointroducedDfcTabpredationongreenturtleeggswasmadeatall acontrolmethodbytrapplngandremovlngaSameanOf threesites．1dentifLCation ofcrabspecieswas based on PrOteCtingturtEeeggsfrombeingp「edatedbyghostcrabs・thefle［d keys（Lovett】1981）andthecharacteristicsof ln PeninsularMalaysia．theghostcrabs（Ocypodespp） burrows（John．1998）．The species Ocypode liveindeepburrowsonsandybeachesofbothmainland CeratOPhtharmusischaractensedbyhavingapyramid－1ike and offshoreislands． Sand mound adjacentorclosetothe burrow．whereas Ocypodekuhliicoversitsburrowholewith a moundof TheobJeCtiveofthisstudywastoquantifyghost Sand．0．ceratophthalmusisusuallyfoundintheintertidal Crabpredationongreentur［leeggsatanestingbeach ZOneandhasprominenteyestalkswithaLongstem．The （MakKepit）andin hatcheries（GeligaandChendor）Lln Stemisshorterin O．kuhlii．which generally has round addition，aneXPerimentwasconductedbyfenclngaPlot eyes．StridulationisapparentinO▲kuhliiwhereduring Ofhatcheryareavvhereeggswereincubatedwiththe Observation，raSPlngSOundscould be heardfromthe aimtounderstanditseffectonreducingcTabspredation． burrows．0kuhliialso preferstoconstructburrowson lnformation derivedfromitwould be used forhatchery theisolated area，in contrastwith0．ceratophthalmus managementpurposes・ that present everywhere on the beach 97 Nestswereexcavatedandtheircontentsexamined Within aweekafterthe emergence ofhatchlings．The PreSenCeOfcharacteristicsnipmarksoneggshellswere attributed to attack by ghost crabs and were easily distinguishablewith marksleftbytheotherpredator SuChasflreantS．Thesumofthenumbersofunhatched eggsandemptyshellsremovedfromanestusedasan approximation oftotalclutchsize（Fowler，1979）．The incubationofC．mydaseggsfor214cIutchestoDkplace atMakKepitbeachfrom25Marchunti112September 2002．whereasatotalof357clutches（atGeliga）and72 F桓Ure2・加eよpeJTme／1ね／pわf8rC／1e／1dor／1∂似1eJγ Clutches（atChendor）wereincubated duringthe period OflAprilto13September，andlAprilto6September， 2002，reSPeCtively．The emergence success was RESULTS Calcu［atedaspercentageofeggsthatresultinhatchlings thatemergefromthenest． Incubationparameters－Highemergencesuccess WaSreCOrdedforgreentu111eeggsincubatedatanatura（ Hatchery Experiment beach and two hatcheries（lbblel）．The vaEues range An experimentalp10t WaS COnStruCted within from81・38％（＋22・30）forinsituincubationatMakKepit Chendor’sproductionhatchery．Thetotalareaofthep10t beach，81．87％＋26．35forartiflCialincubationatChendor， WaS15m2（5mx3m）．1twasfenced rightunderthe and82．47％＋18．28forartificia）incubationatGeliga Sand surface with one－meterdepth ofO．5cm（internaJWererelativelyhighandtherewasonlyslightdifference diameter）mesh size ofnetlon plasticto protectcrab among them．The emergence success ofeggsin the encroachment（Figure2）．FifteenfullcIutchesofgreen experimentaEhatcherywas73．52％＋27．52，areduction turtleeggstakenfrom Chendorbeachduringaperiod OfaboutlO％fromthenaturalandhatcheryfiguresand Of26June－29July，2002were transplantedintothe is obviouslydepicted bya sIgniflCantSmallnumbersof experimentalhatchery．The quantification of crab theincubated eggs．The mean depth ofnestsin both Predationinthee〉（Perimentalhatcheryfollowed similar hatcherieswasin a rangeof13－16cm shalloweTthan marmers as described for clutches on the natural that of nests on naturalbeach． beaches and production hatcheries．

Tablel：A summary oftheincubation parameters and crab predation on green turtle（Chelonia mydas）eggsincubated on naturalbeaclland turtle hatcheries

Paramete「 MakKepitBeach GeligaHatchery ChendorHatchery E叩erimenlalHalchery lbtalno．of clutches 214 357 72 15 1もtalno．ofeggs 20，294 33，409 6，549 1．374 Mean clutch size 96．6 93．6 91．0 91．6 Meannestdepth（Cm） 76．7 60．2 63．1 61．0 Mean Emergence 81．38％ 82．47％ 81．87％ 73．52％

SuCCeSS S．D．（Standarddeviation） ！22．30 ！18，28 ！26．35 ！27．32

No．ofnestspredated 78（36．0％） 81（22．7％） 36（50．0％） 0 bycrabs

No．ofeg9Sp「edated 244（1．0％） 145（0．4％） 180（2．7％） 0 byc「abs

Range（C「ab－P「edated 0－6 0－7 0－23 0 e∈IgS／clutch）

Meanno．ofeggs／cIutch 1．14 0．41 2．50 0 Predatedbycrabs S．D．（Standarddeviation） ！1．80 ！0．93 ！4．19 98

Crab predation WerenOtimportantpredatorstogreenturtleeggsasthe Crabpredationongreenturtleeggsincubatedat mortalityrateofO．4％－2．7％orl・3％overalrwasvery allsitesis summarisedinlbblel．Nest examinations littLe．Sucha10WmOrtalitycouldpTObablybeassociated madeon643clutchesofturtIeeggsfromanaturarbeach with the presenceofhuman being（theworkers）that andtwoproductionhatcheriesrevealedthatthemortality lookedafterallthree－hatchlingproduction sites．Result Ofeg9Sdueto ghostcrab predation wasverysmal［・ OfthisstudyisincontrasttoJohn（1966）whoreported Thisisreflectedbythemeanvaluesofthepredationrate thatghostcrabs，Oqpodewe「ethemostprominentnest thatrangesfrom O，4％－2，7％onlyoTl．3％combined． Predators，COntributing56．67％ofnestmortalityatChagar These figures weTe derived fromindividualsite that Hutang．aturtIebeachlocatednexttoMakKepitbeach， TeCOrdedeggdepTedationatChendorhatcheryas2．7％ both areon theisland ofPulau Redang．The probable fo”owed byMakKepitand GeIigaasl．0％and O，4％， answertothe ghostcrab－humaninteractionis aLso respectively．The varues ofthe percentage ofeggs foundina reportofCornelius（1986）whostatedthat Predated byc「absseemedinagreementwiththemean ghostcrabshavebeenreportedtobeprominentpredators numbers ofpredated eggs perclutch，i．e，2．5＋4．19OfturtIeeggsinareaswherebiggerpredatorsareab－ eggs／CIutch（n＝72），1．14＋1．8eggs／clutch（n＝214）and SentOrSParSe．GhostcrabburrowsDCCurnngneartUrtle O．41＋0．93eggs／clutch（n＝357）． nests throughout the incubation period provide an entrance for other predators to infest or prey on the The percenta9e Of nests being predated by nest．John（1966）reportedthatghostcrabdensityat CrabsseemedhighestforthoseinthehatcheryatChendor ChagarHutang beach ontheislandofPulau Redang （50．0％），followed by the naturalnests at Mak Kepit WaShighestatthebeginningofthenestingseason（jn （36．0％）andinthehatcheryatGeriga（22．7％）．Similarly， May）withacountof177．88crabs／100m．Thedensity the rangeforcrab－Predated eggs／clutch was recordeddecreased throughoutthefo1low【ng mOnthswith43．44 highestatChendorhatchery（0－23eggs／clutch）・OntheCrabs／100minOctober，Thedropmaybelargelydueto Otherhand，SuChavaluewasslightlyhigheratGeliga theincreaseinhumanactivitiesonthebeachduringthe hatchery（0－7eggs／clutch），followedbyMakKepitbeach nestingseason．Hughes（1966）aFsoreportedthatghost （OL6eggs／Clutch）．Twospeciesofghostcrabs．i・e・，0・ Crab activity［S COrrelated with human or predator CeratOPhtha／mus and Okuhliiwere recorded during activity．Thebreeding cycle Dfthespeciesitselfcould thisstudybutefForttounderstandthemagnitudeofegg have caused a dec［inein abundance．rtis noted that depredationbyeachspecieswasnotattemptedatthis Ocypodjdae has distinct breeding seasons that are

Sta9e・ reguIated by exogenousfactors（Simons andJones， 1981）．Thepredationofeggsbyghostcrabsinthisstudy An interesting result was recorded at the is considered small if compared with other predators experimentalhatchery．Thedata（lbbIel）cEearlyshowedsuch asvaranidlizardsthat caused51，9％mor［aFityof thattherewas no ghostcrab predation ataIlatthis flatbackturtle，Natatordepressus eggsin Australia Site as reflected by a”15clutches were safely （BlamiresandGuinea．2001）・ incubated．The useplasticmesh netting provedto be effective in deterring ghost crabs from entering the Taking into consideration that the mean fenced hatchery． emergencesuccessofeggsatthreestudiedsiteswas 81．9％．the different of18．1％was derived from the unhatchedeggsthatincludedl・3％crabpredation・FoT DISCUSS10N managernent purposes．a maJOr PrOPOrtion of the Unhatched eggs recorded from this study requires Anumberofbioticandabioticfactorsareknown furtherinvestigationinordertounderstandwhatfactors toaffectnestand egg mor（alityin marinetu「tlesrThe affectingtheirhatching．0pportunisticobservationsmade haterateoftheAt［antic10ggerhead（C．caretta）inSouth duringthestudyperiod recordedsomepTedato「SSuCh CaroEina＼〟aSOnly6．1％（Hopkinset．al．，1979）．Thiswas asfEreantSandvaTanidlizards，besidesrootsandfungl， mainlyduetointensepredationbyanimalpredators・He mayalsocontributetomortalityofturtleeggs・ reportedthatraccoons（Procyonlotor）andghostcrabs （Ocypodequadrata）destroyed56・1％and2・4％ofthe lntheexperimentalhatchery，theuseofsmall OVeraIE458nests．respectively．Poacherstooktherest・meshplasticnet10n（0．5cmdiameter）tofence15clutches lnthisstudy，Wefoundthatghostcrabs（Ocypodespp） （1，374eggs）ofgreenturtlesresultedinzeronumbersof 99 eggsbeing predated byghostcrabs．Themethod has becausethemagnitudeofdepredationisonlyl．3％（range proven effective in preventing crabs from entering theO．4％－2．7％）．Two species of crabs，i．e．，Ocypode nests．ItisbelievedthatminimismgeggmortaEitythrough CeratOPhthaImusand Ocypode kuhliipresent．The use PreVentivemethodismoreappropriatethantrapplngOr OfsmalImeshedplasticnet10nfenclnglSPrOVenefFective removalofpredatorsastheformerisecorfriendlyin in preventing crabs from entering the nests in turtle natu「e． hatcheries．1tissuggestedthatminimisingeggmortality through preventive methodis moreappropriatethan Manyagreethatthereisalinkbetweenghost trappLngOrremOVaIofpredatorsasthefencingismore Crabsandtheotherpredators．Theinitialharmoccurs eco－friendlysound．FurtherstudiesarerequiredtoquantWy when ghostcrabs maketunnelintothe nestchamber magnitude ofegg mortalityduetootherfactorsthat andbreakopenseveraEeggs．Thisbeginsasequenceof contributed a major portion of the unhatched eggs as events，Which normally resultsin entireclutch being reveaLedfrom this study．The nextstepisintroducing destroyedalthoughthecrabmayactual【yeatonlyafew remediaLmeasuresaimlngatPrOducing hatc仙ngswith eggs．Thisdirectaccessintothenestprovided bythe ZerOegg mOrtality． ghostcrabsactasapathwayforsecondarypredators SuCh as redantsandfungi．FungLand harmfulmicroor－ ganismsf．ndasuitablemediumonthebrokeneggsand ACKNOWLEDGEMENTS SPreadslowly，enCOmPaSS■ngeggSatdi仔erentstages ofembryonicdeveropment・Ltseemsthataddress【ngghost TheauthorsacknoⅥ11edgewiththankstheDirector crabissuewouldatthesametimeaddresstheproblems Genera［ofFisheriesMalayslaandtheChiefofMarine associated with other predation． Fishery Resources Development and Management DepartmentfortheirconsistentsuppoTt・ThisstudywouId CONCLUS10NS nothavebeenpossiblewithouttheassistanceoftechnical staffandrangersoftheDepartmentofFisheriesMalay－ Mortalityofgreenturtleeggsinthestudyarea Sia．Wethankal10fthem． duetoghostcrabpredationisnotanimportantthreat

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