ImpactofMarketHuntingonMammalSpeciesin
EquatorialGuinea
JOHNB. FA,*JAVIERJUSTE,tJAIMEPEREZDELVAL,$ANDJAVIERCASTROVIEJOt
jerseyWildlifePreservationTrust,LesAugrèsManor,Trinity,JerseyJE35BF,ChannelIslands,email fEstaciónBiológicadeDoflana,C.S.I.C.,PabeliondelPeru,AparladoPostal1056,41080Sevilla,Spain
*CooperaciónEspafiola,Malabo,GuineaEcuatorial
Absfract TheImpactofcommercial bunting onforestmammalswasstudied intworegionsonBiokoand Rio MuniinEquatorialGuinea,westAfrica.Harvestswereassessedfrom carcasscountsinthemainmarkets intheareas.A totalof10,812carcassesof13specieswererecordedinBioko,and6160carcassesof3Ospecies wererecordedinRioMuni.Biomassofharvested mammalswas111,879.63kginBiokoand64447.87kgin RioMuni.Forthe12preyspeciesselectedforstudyinBioko,harveststotaled 7.15animals/km2or6293kg’ km2.Harvestsforthe17preyspeciesinRioMuniwere3.22anlmal.s/km2or2406kg/km2.Weusedamodel developedbyRobinsonand Redford(1991)toestimatepotential harvestsbasedonanimal productionrates. Totalproductionwas147.90animals/km2and 139.12animals/km2inBiokoand RioMun4respectively.Po tential harvest figuresvaried considerablybyspecies.Comparisonofactual and potentialharvestsshowed thatfiveprimatespecies(CercopithecuserythrotisCercopithecusnictitansCercopithecuspogonias,Cercopith ecus preussi, and Mandriflusleucophaeus) and one ungulate (Cephalophusogilbyl) in Bloko were being buntedunsustainably.Onlytwo ofthe 17species(Cercopithecusnictitansand Cephalophusdorsalis)inRio Muniwerebeing buntedunsustainably.Percentdeviationofactual from potential harvestsaveraged 498 timesgreaterthansustainableharvestinBlokoand 1.03timesgreaterinRioMuni.Forthetwositestogether figuresrangedfrom dose to28timesgreaterthanpotential to0.08%ofthepotential harvest.Althoughbunt ingmethodsand thecommercializationpotential ofspeciesmayaffecttheirpresenceinmarkets, thesefig uresshowthatBiokoanimalsareheavilyexploite4someofthemunsustainably.Thisposessevererisksfor theconservationoftheisland’sunique faunathat mustbeaddressed immediately.
ImpactodeIacazacomercialsobrelasespeciestiemamiferosenGuineaEcuatorial
Resunien:ElimpactodelacazacomercialdemamiferosdeIaselvafue estudiadoendosregiones enBioko y RioMuni,enGuineaEcuatorial,AfricaOccidentalLascosechasfueronestimadasapartirdelconteodean imalesmuertosenlosprincipalesmercadosdelarea.Untotalde10,812animalesmuertosde13especiesfu erondocumentadosenBiokoy6160animalesmuertosde30especiesfuerondocumentadosenRioMuni.La biomasadelosmamiferosrecolectadosfuede111,879 kgenBiokoy66,447.87kgenRioMuni.Paralas12 especlesdepresasseleccionadasparasuestudloenBioko,larecolleccióntotalizó7.15animales/km2o62.93 kg/km2. LarecolecciOnpara his17espedesdepresaenRioMunifuede3.22animales/km2o2406kg/km2. Utilizamosun modelo desarrolladopor Robinson yRedford(199!)para estimarlascosechaspotenciales basadas enlastasasdeproducdtinanimalLaproducción totalfuede 147.90animales/km2y 13912an imales/km2 enBiokoyRioMunirespectivamente.LascifrassabreIacosechapotenclalvarariaronconsi
dne
ranbtleentrelasdistintasespedes. Lascomparacionesdelasrecoleccionesreaiesylaspotenciales mos
traronquecincoespeciesdeprimates(Cercopithecuserythrotis,Cercopithecusnictitans,Cercopithecuspogo nias,CercopithecuspreussiyMandriflusleucophaeus)yunungutado(Cephalophusogilbyi)enBiokoestaban siendocazadasenformano-sostenible.Solamente2dolas17especies(CercopithecusnictitansyCephalophus dorsalis)enRioMunlestabanslendocazadasenformano-sostenible.LadesviaciOndelporcentajedorecole cdonrealconrespectoalpotencial,fueenpromedio498vecesmayoraldolarecolecciOnsostenida enBioko y1.03vecesmayorenRioMuni.Paralosdossitiosfuntos,lascifrasoscilaronentre28vecesmayorquelaco
sechapotenclalaun0.08%tieíacosechapotencial.Sibienlosmétodostiecazay elpotendaltiecomercializa dOn puede afectar sitpresencia enlosmercados,lasdfrasactuatesmuesfran quelosanimalesenBiokoes tanseveramenteexplotados,algunotieloscualesenfonnano-sostenible.Estoplanteaseverosriesgosparahi conservaclOntieíasingularfaunadehiida,portoqueesteprobtemadebesertratadoenformainmediata.
Introduction Methods
FaetaL
Wildanimalsareanimportantsourceofproteininmany tropicalforest countries inAfrica(Ajayi1971, 1983; AdeolaDecker1987).Forexploitedspecies,itisim portantthattherateofharvestdoesnotexceed thatof productionbecause over-exploitationleadstodepletion. Harvestshould beareplaceableformofmortalityand shouldsubstituteforsomeofthenatural,annualmortal ityratherthanincreasingtotalmortalityofapopulation (Caughley1977).
Robinsonand Redford(1991) developed a simple modeltoprovideestimatesofpotential (sustainable) harvest ratesfordifferentneotropicalforestmammals. Theyfocusedonspeciestraditionallyimportanttosub sistence huntersandcalculated maximum production foraspecies(innumbersofanimals/kin2)asthenumber producedyearlyunderoptimalconditions.Theyused measuresofpopulationdensityandtheintrinsic rateof natural increasetoestimatepotential harvest rates for differentspecies.Thisprovidesafigurefortheoptimum sustainableharvestwhen productionisatamaximum andharvestinghasminimaleffectsonthenaturalpopu lation.Theoptimumsustainable population isthenum berofanimalsofaspeciesthatresultsinmaximumpro ductivitybutnotexceedingthecarryingcapacityofthe habitat.Assessingtheimpactofhuntingonwildlifepop ulationsisthuspossiblewhenfiguresgenerated bythe modelarecompared toactualharvestdata.Thesecom parisonsareusefulinsituationsinwhich detailedlife- historyparametersforaccurateestimatesoftheeffectof huntingonpopulation structurearenotavailable.
Incountrieswhere commercial hunting ofgamefor
human consumption is important, datafrommarkets canprovideshort-andlong-terminsightintotheimpact ofhunting onbushmenspecies.InAfrica, countsof numbers ofmammals,birds,andreptilesenteringmar ketscanprovide understandingofseasonalandlongitu dinaldynamicsofwildlifeuseandexploitation(Colynet al.1987;Kalivesse1991)andeventhebiologyofspecies (Gevaerts1992). Weexamined theimpactofharvests forsomemammalspecies byrelatingcalculatedpoten tialharvests withactualtakelevels.Weexamined only thosespeciesthatcomprised aminimumof1.5%ofthe totalweight ofgametakenandforwhich dataonden sityandlife-historyparameterswereavailable.
StudyArea
EquatorialGuineaconsists ofaterritory ontheAfrican mainland, RioMuni,(26017 km5andfiveislands.Rio MuniisborderedbyCameroon tothenorth, Gabonto theeastandsouth, andtheGulfofGuineatothewest. ThetwomostimportantislandsareBioko (formerly Fernando P00, 2017 2)andAnnobon (formerly Pa galü,17km2).Intacttropicalrainforestisfoundafewki lometersinlandfromthecoastandstillcoversmostof the country,59% of RioMimiand28%ofBioko.Al thoughtheamountofprimaryrainforestinBiokoislow, becausemostforestwascuttoplantcacao,mostofthe islandiscoveredinwell-conserved, tallsecondaryforest (Fal992a).
HarvestData
HuntinginEquatorialGuineaIspracticedopenlyandin tensivelybyprofessionalhunters, andmeat isbrought intomarketsthroughouttheyear.Unlikeother West Af ricancountries, therearenoclosedhuntingseasons.
FromOctober1990throughOctober1991,harvestin formation was collected fromtwo marketsites(Mun doasiandCentral)inBats,RioMuni,andfromtheprin cipalmarket(MercadoCentral)inMalabo,BiokoIsland. Thelattermarketisdivided intoseparatesections(Luba andRiaba).
Vertebratecarcasseswerecountedbytheauthorsand bytrained,localobservers hmiliar withallentrypoints ofbushineattothemarketsandthespeciesconcerned. Reliability was checked regularly.Species were re cordedbytheircommon names toavoidconfusionin nomenclature.Samplingwasconductedon424market days, 212ateachlocality.Gamewasbroughtin dailyby intennediariesbetween hunters andmarket-standpro prietors.Wevisitedthe marketsdailybetween 0630 hoursand1200hoursbecauseallmeatarrivestobesold between0700and1100everymorning. Only freshcar casseswerecounted,although somesmokedmeatis broughtin. Numbersof carcassesrecordedrepresent minimumextractionbecausesomegameisconsumedin villagesorsoldbeforeitreaches themarket(Colelletal.
1995).Ageandsexinformationwasnotrecorded.No
menclaturefollowsHaltenorthandDiller(1987).
Analysis
Preyspecies biomasswascalculated bymultiplying the numberofanimalsbytheindividualspeciesweights.Be cause assome ofthe carcasses forsaleareyoung ani mals,thismethodtendstooverestimatethetotalweight ofmeatsold.
Huntingareasthatsupplythemarketsitesweredesig nated “reservoirareas.”Marketspecies restricted tonv erineorswamp forests(collared mangabey,Cercocebus torquatus;DeBrazza’smonkey, Cercopitbecusnegiec
nlterateofincreaseistheexponential oftheintrinsic rateofIncrease (e,...)andistheincreaseinthepopula tionsizefromtimettotimet±1.Variablessuchasden sityandintrinsicrateofincreaseinmammalshavebeen showntobepredictablyrelatedtotheirbodymassand trophicleveloccupied (Peters1983;RobinsonRed ford1986). Maximumfiniterateofincreasewascalcu latedusingageatfirstbirth(a),ageatlastreproduction (w), andbirthrateoffemaleoffspring(b)from Cole’s (1954)equation.
rm(w+1)
ins; water chevrotain, Hymoschus aquaticus; grey-
checkedrnangabey, Lophocebusaibigena; otter, Lutra maculicolils; talapoin, Miopitbecustalapoin; Bates’ dwarf antelope,Neotragusbatesi; sitatunga, Tragela phus spekel) were not included in these analyses be causeofdifficultiesinmeasuringthesizeofthese areas. Thesizeofternfirmeareaswasdetermined,conserva tively,frominterviews withhunters,in bothlocalities.
InBioko, hunterssending meat to the Lubamarket
section use the Malabo/Luba districts, especially the western slopesofPicoBasiléandthenorthernslopesof theGranCalderadeLuba.Theisland’seastern districts ofBaneyandRiabaandareasstretchingintothesouth eastern highlandsandcoastservetheRiabamarketsec tion.InRioMuni,meatprimarilyfromtheLitoraLdistrict (S2,000km2)enters both markets. BecauseBiokopri matesarerestricted tocertain partsoftheisland,distri bution data gathered by Butynski and Koster (1995) wereusedtocalculatereservoirareasforthesespecies.
Productionforeachspecies wasdeterminedusingin formation on populationdensity at carrying capacity, themaximum rateofpopulationincrease, andtheden sity that producesthe maximum sustained yield.We useddataonobserved densities ofspecies, asopposed topredicteddensities (seeRobinson Redford1991). Avengedensities (numberofanimals/kin2)were taken from anextensive surveyofthe relevant literature.No densityinformation wasobtained forDendrobyraxdot- sails,Crossarchus spp., Man/s gigantea,andThriono mysswinderianus,sothesespecies werenotincluded. Optimum harvest wasconsideredthenumber ofani maLsofaspeciesthatcanberemoved(perkilometer)by humanseveryyearwithout alteringthesizeofthestand ingpopulationandwasdeterminedusingRobinsonand Redford’s (1991) harvest model. Tocalculate produc tion(P,theaddition tothepopulation through births andimmigntions),these authors assumed that realistic maximumfigureswouldoccurat60%carryingcapacity to accommodate variation related to density depen
denceandbirthrates.Hence,
“max(0.6 DXImax)— 0.6 D,
where Disthe populationdensity and imaxthe maxi
mumfiniterateofincrease ofthespecies. Maximumfi
1em+beTm—bC
Forthecalculation ofr,,femaleageatfirstrepro ductionand totalnumber ofinfantsbornperyearwere takenfrom avariety of sources. Figuresforprimates camefromreferencescontainedinRoss(1988, 1992); thoseforduikers werederivedfromPayne(1992). For rodents,pangolins,andcarnivores,information wasex tractedfromEstes (1991) andNowakandParadiso (1992).Annualfemalebirthrate(numberoffemaleoff springbornperyear)wascalculatedfrommeaninter- birthintervalandlittersize,andweassumedthatallspe cieshaveasexratioatbirthof1:1. Dataonageatlast reproductionisnotusuallyavailableformostspecies, butlongevityismoreoftenrecorded.Thcrcfore,maxi mumrecordedlongevity,L,wasusedasasubstitutefor w when we calculated rm,as employed by Ross (1992).DatausedaregiveninTable1.
Potentialharvestwascalculatedfrom productionfig ures.Becausethelongevityofaspeciesisagoodindex of theextent to which harvestingtakesanimals that would have died anyway (species were divided into threecategories:long-lived,>10years;short-lived,5-10 years;andveryshort-lived<5years),RobinsonRed ford(1991)assumedthatharvestcouldtake60% ofthe production in veryshort-livedspecies, 40%inshort- lived,and20%inlong-lived.
Exploitationlevelsofeachpreyspecieswereassessed bycomparingproductionfiguresforeachspecieswith thevolumeobservedinmarkets.ThisyieLdedafigure thatwasconvertedto apercentagetodenotethedevia tionofactualfrompotentialharvests.
Results
ThirteenspeciesofmammalsinBiokoIslandand29(in cludingtheeightriverine species)inRioMimiwere recorded(Justeetal.1995). Fivespecies (38.5%),in cludingendemic subspecies such asPreuss’sguenon (Cercopitbecus preussi insularis),russet-eared guenon (Cercopitbecus eiytbrotiserytbrotis),drill(Mandriltus leucopbaeuspoensls),andredcolobus(Procolabusisa diuspennanti),wereuniquetoBioko,whereas24(82.8%) werefoundonlyinthecontinental sites.
Table1. Bodymass,dietclassification,andreproductivecharacteristicsofmammalspeciesusedasbushmenIaEquatorialGuinea
Rodentia
*CA,carnivore,FG,fruglvore-granlvore;FH,frugfvore-berflvore;FO,fruglvore-omnivore;HB,herbivore-browser;MY myrmecophage.
Wecounted17,571 carcasses (10,812 in Biokoand
6760inRioMuni),ofwhich artiodactyls(9species)ac
countedfor 36.7%,followed by primates (16 species,
26.2%)androdents(3species,21.2%)(fable2).
Annualharvestwas12,974animals(111,879.63 kg)in Biokoand8112(66,447.87kg)inRioMuni(p0.001). Harvestsconsisted of6.49animals/km2or55.94kg/km2 inBiokoand 3.89animals/km2or33.22kg/km2inRio Muni (cia-square test, p0.001). The blue duiker (Cephalopirns monticota)and Ernin’srat(Cricetomys
therodentsandartiodactyls;thelowestfigureswerere
cordedforprimates.
Figure1shows the percentage deviationof actual takesfrompotential harvestforallspeciesinBiokoand Rio Munimarkets.Percentagedeviationofactualfrom
Table2. Numberofspedes(S)andIndividuals(N)Inmammalian groupsavailable Inmarketsites InBloke(LubaandRiaba)andRio MunI(CentralandMundoasi).
etnini)inBioko,andC.monticolaandthebrush-tailed porcupine (Atberurus africanus) in Rio Muni, ac
GroupSN
Luba
SN
Riaba
SN%
Totals
countedformorethanhalfofallcarcassesbrought into
markets(Justeetal.1995).Cephalophusmonticola was themostnumerous speciesinbothmarketsites,repre senting approximately30%ineach. (Jricetoniys emini wasthesecond mostcommon inBiokobutrankedonly
Artioclactyla Primates Pholidota Hyracoidea Rodentia Totals
22134 34.70
71652 26.87
1 119 1.94
17 0.11
22237 36.38
136149
21779 38.15
7 1044 22.39
173 1.57
14 0.09
21763 37.81
13 4663
23913 36.19
72696 24.94
1192 1,78
1It 0.10
24000 36.99
13 10,812
eighthinRioMuni.Threespecies,C.monticola,C.em-
Central Mundoasi Totals
casseson saleon the island.Cephalophusmonticola, A.africanus,andthegreaterwhite-nosed monkey(Cer copitbecusnictitans)representedmorethan 59%ofall carcassesinRioMuni.
Production and potential harvest estimates aregiven
Artiodactyla 81294 41.29 81594 43.95 8
Primates10 790 25.21 II 738 20.35 11
Carnivora443 1.37 478 2.15 5
Edentata256 1.79 256 1.54 2
Hyracoidea11 0.03 11 0.03 1
Rodentia3 950 30.31 31160 30.86 3
2888 42.73
1526 22.58
121 1.79
112 1.66
2 0.03
2110 31.22
InTable3.Thehighproductionfigureswere typicalof
ConservationBiology
Volume9,No.5,Octoberfl)95
TOTALS28313429 362730 6759
Table3. ComparIsonsofobservedhrvcst,cakvlatcdproduction,andsustalanbfrharvestforbushineatspecIesinEquatorialGuinea.
Observed / Observed / AnimalsHarvested / Biomass
Harvested / Production
Siteand Species / Density(nolkm2) / Harvest(no/yr) / (perkm2) / (gms/1m2) / (no,m2)
BIOKO
PrImates
Cercopitbecuserytbrotis / 24.70 / 781 / 0.16 / 683.68 / 2.64
Cercopfthecusnictltans / 22.70 / 254 / 0.49 / 4263.00 / 0.12
Cercopithecuspogonias / 14.40 / 52 / 0.56 / 753.76 / 0.08
Cercopitbecuspreussi / 9.90 / 196 / 0.65 / 6272.50 / 1.51
Cobbussatanas / 20.40 / 514 / 0.29 / 3480.00 / 2.72
Mandrillusleucopbaeus / 6.70 / 551 / 0.29 / 4328.25 / 0.79
Procobobuspennanti / 156.30 / 348 / 0.66 / 5273.07 / 14.09
Rodentla
Atberurusafricanus / 55.00 / 1581 / 0.79 / 3160.00 / 27.12
Cricelomysemini / 134.00 / 2419 / 1.21 / 2420.00 / 81.49
Ardodactyla
Cepbabopbusogilbyi / 13.00 / 3181 / 1.59 / 30210.00 / 2.02
Cephabophusmonticola / 22.60 / 732 / 0.37 / 1850.00 / 8.68
PholMota
Manistricuspis / 10.90 / 192 / 0.10 / 240.00 / 6.63
TOTAlS / 490.60 / 10,801.00 / 7.15 / 62,934.26 / 147.90
RIOMUM
Cercopitbecuscephus / 17.30 / 430 / 0.22 / 1193.25 / 1.18
Cercopitbecus mona / 13.00 / 67 / 0.03 / 91.56 / 0.89
Cercopitbecus nictit.ans / 22.70 / 523 / 0.26 / 2275.05 / 1.55
Cobbussatanas / 20.40 / 152 / 0.08 / 912,00 / 2.72
Gorillagorilla / 0.70 / 3 / 0.00 / 176.32 / 0.03
Mandrillussphinx / 6.70 / 262 / 0.13 / 2153.64 / 0.79
Pholidota
Manistrlscuspis / 10.90 / 93 / 0.05 / 116.25 / 6.63
Ardodacb
Cephabophusdorsalls / 3.80 / 491 / 0.25 / 4910.00 / 0.50
Cepbabopbusleucogaste / 4.10 / 6 / 0.00 / 40.50 / 1.31
Cephalopbussylvicultor / 0.90 / 6 / 0.00 / 187.50 / 0.29
Cephubopbusmonticola / 22.60 / 2107 / 1.05 / 5267.50 / 8.57
Potamochoerusporcus / 3.10 / 93 / 0.05 / 2790.00 / 1.89
Rodentla
Atberurusafricanus / 55.00 / 1698 / 0.85 / 3396.00 / 27.12
Cricetomysemlni / 134.00 / 390 / 0.20 / 390.00 / 81.49
Carnivora
Genetta servallna / 0.80 / 32 / 0.02 / 16.00 / 0.45
Nandiniabinotata / 3.60 / 72 / 0.04 / 72.00 / 2.01
Civecitictiscivetta / 2.80 / 15 / 0.01 / 75.00 / 1.68
TOTAI.S / ,322.40 / 6440.00 / 3.22 / 24,062.57 / 139.12
potential harvests averaged 498.99% in Bioko and
103.27%inRio Muni.Huntinglevelsdifferedbetween taxonomicgroups;Prinutesandungulates appearedto bethemostexploited.InBloko,estimatesofactualtake forallexcept fourprimates and oneungulate(30.7%of allrecorded species) were below potential harvests. Takesrangedfrom28timesgreaterthansustainablehar vestforthecrownedguenon(Cercopitbecuspogontas) to0.96timeslessthanthesustainable harvestforEmin’s
Rio Mum presentsadifferentpicturethanBiokobe causeonlytwospecies (11.77%)were beingexploited in an unsustainablemanner:Cercoplt1.ecus nictitans andthebayduiker(Cephalophus dorsalts).Mostspe
des werehuntedbelow sustainableharvests.Takes rangedfrom 13limesgreaterthanpotentialharvestfor C dorsalis to0.67 timesbelow potentialharvestfor Cepbalopbusleucogaster.
Discussion
Thereare fewdetailedstudies atpresentontheimpact ofhumanexploitationongameanimalsinwestAfrican countries.Assessmentsofoptimalsustainable harvests usingtheRobinsonand Redford(1991)modelcan offer well-founded baselineinformationforregulatingpopula tion-uselevels.Assuggested byRobinson andRedford
1112MarkeilluntingofAfricanBushmeatspeeiesPaelat.
Cpo CprCogMieCnICsaCerPpeAelCmoMrCern
Cni Cdo CceMapGgoCmnQseCmo Aaf Csa Nbi Ppo Mfr Cci Cam Cay CI.
Species
Figure1. Deviation of actualharvestfromcalculatedpotentialharvestsforbusbmeatspeciesinBioko(a)andRio Muff(b).Speciesabbreviations:AafAtherurusafricanus;Cce,Cercopithecuscephus,Cci,Civecttictiscivetta;Cdo, Cepha[ophusdorsaiis,Cer,Cercopithecuserythrotis;Cern,Cricetomysemini,Cle,Cephalophus[eucogaster;Cmn,Cer copithecusmona;Cmo,Cephalophusmonticola,-Cm Cercopithecusnictitans;Cog,Cephalophusogilbyi,Cpo, Cercop ithecuspogonias;Cpr,Cercopithecuspreussi;Csa,Colobussatanas,Csy,Cephalophussylvicultor, Ddo,Dendrohyrax dorsalisGgo,Gorillagorilla;Gse,Genettaservalina;Mie,Mandrillusleucophacus;Msp,Mandrillussphin,çMtr,Manis thcuspis,Nbi,Nandiniabinotata;Ppe,Procolobuspennanti;Ppo,Potamochoerusporcus.
ConservationBinlogy
Vc.lume9,Nc’,5,Ocer19
(1991),eventhoughthedataaresubjecttovariationasa resultofinaccuraciesinestimation, theassumptionsin themodelareinlinewithproductivityawlharvestinfor mationfromotherecosystems.Acautionarynoteisnec essary,however.Potential harvests, the maximum bio logicallypossible productionfor agivenspecies under ideal conditionscalculated herein, incorporatefigures thatrelatetoreproductionparametersassumedtobeac curate andthatuseavengepopulationdensities.
Currentdatapointtoacleardifferenceinexploitation
ofspecies betweenBioko andRioMuni.Varianceinto talnumberofpreyspeciesrecorded betweenislandand continentalmarkets relatesdirectly tothe richer verte bratefaunainRioMuni(Fa1992a).Butit isclearthatall marketsrelyheavilyonthesaleoftwospecies, anante lope (Cepbalophusmonticola)and arodent (Criceto mysemini)inBioko andthesameantelopeandanother rodent(Atberurusafricanus)inRioMimi.
Unless reproductiveparametersreportedherein are
verydifferentfromactualfigures,thecurrent rateof hunting iscertainly farbeyondthe abffityofsomespe ciestosustainpopulations. Ourfiguresfortheduiker species in Bioko,are below those observed by Payne (1992)fromastudyinnearbyKorup, Cameroon. Payne (1992) calculated a higher take of 11.5-13.2 times greater thanthesustainable harvestforC ogilbyi (1.96 timesgreaterInourstudy)and1.3-2.2timesgreaterfor Cnwnticola(0.11timesgreaterInourstudy).Thesitu ation isdifferent for primates because levelsforsome Biokospeciesarearound twotimesabovepotential har vest,buttakeforCpogonlasis28timesabovesustain ableharvest.Thisspecies, together withC.nictitans,C. perussi,andMandrilluleucophaeus,isunsustainablyex ploited; thelasttwospecies areamongthemostendan geredprimatesinAfrica(Oates1986;Leeetal.1988).
Exploitation levelsgeneratedfrom themodelassume generallyunburnedconditions, butinrealityactualden sitiesarewellbelowwhatthemodelassumes,andthere- foretheeffectofhuntingonthese speciesmustbeseen ascvenmore worrisome. Becauseanydisruptionofthe population(skewed sex ratios,isolatedsmallgroups of
EquatorialGuinea(Castroviejoetal.1986;JusteCan- tern1991;Fa I992a). Nevertheless,proteindeficiency exists,particularlyawayfromthemain urbancenters (CooperationFrançalse1984),becausehalfof allprotein intheurbanareasisderivedfrombushineatwhereas the sameamount invillagescomesfromprotein-rich oleagi nousgrains(peanutsandsquash).Thisseemingcontra dictionistheresultnotofa lowper-capitaavailabilityof meatinruralareasbutofanemphasisonsellingpreyin towns because ofthegreater purchasingpower there. Thisisclear ifone comparesthe volume ofextracted meatbetweenlocalities.ThemeatvolumeattheMalabo markets inBiokowas 70%higher than the volume in Bata,despite onlyaslightdifference inpopulationsize betweenMalaboand Barn(52,000 and 55,000, respec tively;datafromFNUAP).Malaboistheseatofgovern ment andforeign aidorganizations;therefore, ithasa more urbanized populationwithgreater buyingpower. Thus,the rateofmeatextractionrespondstothe eco nomicpotentialofaproportionoftheurbanpopulation rather thantothenutritionaldemands ofthepopulation atlarge.
Attributes of species that influence hunters’ prey choiceare difficulttodetermine, butspeciesfoundin marketsbothontheislandandincontinentalareasmay representonlythoseanimalsthatfailwithinaparticular weightrange,dictatedby huntingchoiceoreconomic constraints(such astransport costs) rather than—or as wellas—market preferences.JusteandCantero (1991) arguefortheexistenceofanoptimalpreyspectrumde termined bymeatsale prices between1000 and1500
FCFAperkg($US3-5).Thus,smallerpreysuchassquIr
rels(8speciesinBloko andiiinRioMuni) andbats(Fa
1992a), aswellasthelargeanimals(>200kg)areex cluded, andmoreemphasisisputonmedium-sizedani Both size extremesrequire specialized hunting techniques.Thehirgerspecies (forexample, theforest buffalo[Syncerus caffernanus]andthe forestelephant [Loxodonta africana c-yclotisJrequireanexaggerated investmentinextractionandtransporttomarket,Hence, species appearingin markets are generally easily
animals,orincreased mortalityofpre-reproductIveani-tracted through theuseoftrapsandsnares(rats,porcu
mals)mayhavealreadyaffectedproductioninthereser-pines, duikers) or have acceptableeconomicreturns. voirareas, over-hunting ofsome species maybe even Peop1es preferenceforcertain meatsmayalsoaffectse than we have shown. Furthermore, be- lectionofspeciestakentomarkets(SabaterPiGroves
causeactual harvestfiguresare minimal(more animals thanappearinmarketsaretaken),current ratesofhunt ingfaroutstrip the abilityof some populationsto re place the animalskilled.Datafrom Colelletal.(1995) demonstratethat whereas 80%ofantelopescaught in villagesinsouthernBioko weresenttomarket, just10% of thesmallergame(Criceromys,Manis)weresoldat market.Thishasalsobeen observed inZaire(Colynet a!.1987).
Our study hasfurther confirmed the importanceof bushmcat asasubstantial source ofanimal protein in
1972).Acombinationofthesefactorsaffectsthevarying proportionsofspeciessoldinmarkets.
Hunting technology andmethod (snares versusguns) arerelatedtothesizeoftheanimal.Therefore, aplausi bleargument toexplain over-exploitationofthearbo realguenons andforestbaboons isthathunters actively these animals. Snaretrapping does not require mucheffortandcanbeundertakensimultaneouslywith gun hunting. Snaresarechecked atone-week intervals; thus, huntershave more time to stalk arboreal game (Cold etal.199).
1114MarketHuntingofAfrfcanBushmeatSpeciesPactaL
InRioMuni,over-huntingseemslesssevere,butas earlyas1968Sabater P1andGroves(1972) notedthat heavypredationofguenonsby humanshadmadethese smallmonkeysrareinsomeareas. Afurther indication oftheimpactofhuntingonBiokoguenonsIsthatdensi tiesinundisturbedareasareshowntobethree tofour timeshigherthaninareaswherehunting ispresent(Bu tynskiKoster1995),despItethefactthatguns andam munition are not readilyavailable(Juste Cantero
1991).
Ifharvestcontrolsarenotimposed,increases inhu manpopulation,changesinaboriginalsubsistencemeans, andsubsequentdeforestationwillimpoverish native fauna,astheyhaveinothertropicalcountries(forexam ple,Panama;Bennett1968).Ingeneral,fiunal exploita donforsubsistenceinWestAfricaisconsideredhighby severalauthors(Mittermeier1989),butitisthegreater emphasisonhuntingforprofitthatisdisquieting.This hasbecomemore conunonpiacebecause commercial huntingoffersasignificantmonetaryincentivetorural people.Wilkieetal.(1992) hasshown thathuntingin Congoconstitutesthemajorrevenueforupto51%of theemployeesofamajor loggingcompany.Without theseearningsmanyfamilieswouldbeunabletobuyba siccookingutensils,clothing,medicine,andeducational materialsforschool-agechildren.
Aneffectivewaytoprotectandexploitgamesustain- ablyinEquatorialGuineamaybethemaintenanceofal readydecreedprotectedareas,especiallyontheisland, wherecontrolofhuntingisvitalforconservingtheen demicfauna.Established,protectiveboundaries(Castro viejoetal.1986;Fa1992a,199Th)mustbemadeeffec tive, althoughexploitationin someareascouldcontinue onarotationalbasisinwhichMiowareasserveasrepro ductiverefuges.Mostareas,however,atleastinBioko, arebeinghuntedcontinuouslyandintensively,andfew sitesmayremainassourcepopulationsthatcouldre populatetheheavilyhuntedareas.Dataonactualdensi tiesandharvestratesfromspecific sitesareurgently needed.Moreimportant,althoughItwillbemorediffi cult,huntingandmonitoringregulationsneedtobees tablished.
Acknowledgments
WethankJoséAngueMangueinBiokoandRafaelDel gado,AntonioOndó,PascualSacogo,andCornelloCis nerosinRioMuniforcollectingthedailymarketinfor mation.WearegratefultotheMinisterof Cultureofthe Republicof Equatorial Guinea,Excmo,LeandroMbo nile,andtheDelegadoContinentallilmo.WethankJosé Obamaforhelpandsupport.Thisstudywasfundedby theO.C.G.E.,atpresentthe Institute deCooperación panciDesarroilo(LC.D.)oftheSpanishMinisteriotie AsuntosExteriores.WealsothankCarolineRossforpro-
vidinguswith computerprogramsandJohnRobinson andJohnPayneforreviewingearlierdraftsofthemanu script.
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