SEA FARMING AND SEA RANCHING SYSTEMS IN CHINA.docx
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SEA FARMING AND SEA RANCHING SYSTEMS IN CHINA.docx
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SEAFARMINGANDSEARANCHINGSYSTEMSINCHINA
SEAFARMINGANDSEARANCHINGSYSTEMS
INCHINA
Thechoiceofaparticularculturalsystemforseafarmingorsearanchingdependsonseveralfactorssuchasexistingnaturalconditions,availabilityoffinancialsupportandeducation/trainingleveloffishermen.InChina,severalculturalsystemsarenowcommonlyadopted.
SeafarmingandsearanchingsystemsinChina
System
Culturedorganisms
Productionscale
Pondculture
Fish,shrimp,crab,molluscs,Gracilariaspp.
Commercial
Floatingraftculture
Seaweed,scallop,oyster,abalone
Commercial
Mudflatculture
Laver,razorclam,hardshellclam,oyster
Commercial
Penculture
Abalone,shrimp
Commercial
Inshorecageculture
Fish
Commercial
Offshorecageculture
Fish
Commercialandtrials
Tunnelculture
Abalone
Smallscale
Submergedcageculture
Abalone,fish
Smallscale(trials)
Indoortankculturewithwaterrecirculation
Flounder,turbotandotherfish,abalone
Commercialandtrials
Seabottomcultureandsearanching
Abalone,Japanesescallop,giantcockle,seacucumber,seaurchin
Commercial
Stockenhancement
Chineseshrimp,redseabream,flounder,largeyellowcroaker,mullet,jellyfish
Trials
1PondCulture
Ahighproportionoftheareaundercultivationisdevotedtopondcultureinmarineandbrackishwaters.Mostpondsarebuiltinmudflatareasandusedforfarmingshrimpandcrab.Asmallerareaproducesfish,molluscsandseaweed.Pondsarefedseawatereitherastidalpondsorbypumping.
Sincetheearly1980s,pondculturedevelopedrapidlythroughoutthecountrynotonlybecauseitstechnologywasrelativelysimpleanditrequiredlessinvestmentsbutalsobecauseofthetraditionalknowledgeoffishpondculturewhichexistedinChina.Anamplesupplyofpenaeidshrimppostlarvaeandprofitableeconomicreturnsfromshrimpculturefurtherstimulateddevelopment.
Butoverexploitationandpollutionofnaturalresourcesopenedthewaytovariousdiseasesandinparticulartothe1993viralepidemics.Thelatterledpolicymakers,investorsandfarmerstoreviewexistingpoliciesandculturalsystems.Nearly10yearslater,peopleagreethatitisindispensabletopaymoreattentiontobio-ecologicalprotection,tosocio-economicaspectsand,ingeneral,toallfactorswhichmightimpactonsustainabledevelopment.
2FloatingRaftCulture
Thereisalonghistoryofusingfloatingraftsforshallow-seafarming.Thissystemcanbeusedforavarietyofspeciessuchasseaweed(kelpandlaver),filteringorganisms(scallop,oyster,mussel)andabalone,combinedwithcultureinsmallsubmergedcages(lanterncages).
Thesystemiswidelyadoptedforfarmingkelp,oyster,scallop,abalone,etc.Thesespeciesbeingeitherautotrophicorfilteringorganisms,thereisnopollutionoftheenvironment,particularlywithkelpfarmingasmentionedbefore.
3MudFlatCulture
Thissystemisespeciallysuitableforfarmingbenthicspeciessuchasbloodcockle(Tegillareagranosa),hard-shelledclam(Meretrixmeretrix),manilaclam(Ruditapesphilippinarum),razorclam(Sinonovaculaconstricta)andseaweedsuchasPorphyraspp.ItisverypopularinChinabecauseitdoesnotrequirelargequantitiesoffoodanditdoesnotpollutetheenvironment.
Beforethe1980s,mudflatculturewaslimitedtoparticularareasbecauseofthedifficultytoobtainseedwhichhadtobecollectedfromwildstocks.Theseedsupplyisnowgreatlyimproved.Forbloodcockle,Cyclinasinensis,seedareproducedonacommercialscale.Forotherspeciesincludinghard-shellclamandmanilaclam,protectingwildbroodstockhasbeenaneffectivewaytoenhanceseedproduction.Forrazorclam,whichhasbeenfarmedinChinafordecades,wildseedarecollectedfollowingarathersophisticatedsysteminvolvingsiteselection,smootheningthespawningarea,forecastingseedsettling,collectingandtransportingseed.
Ingeneral,themudflatecologicalsystemisrathervulnerable,lyingattheinterfacebetweenseaandland.Forexample,insomeareas,mudflatshavebeenblindlyexploited,evenoverexploited,forshrimpfarmingwhichhasresultedindestroyingtheoriginalecologicalsystemandshrimpfarmingitself.Thishasoccurredtoofrequentlyandnowwehavetogiveprioritytotheprotectionofmudflatandmangroveforestareas.
4PenCulture
Sitesforpencultureareselectedinintertidalareaswherelowfencesandwatergatesarebuilt.Atlowtide,waterdepthdropstoaminimumof50to80cminsidethepens.Asthenexthightidalwaterstartscoming,itentersthepenswherewaterdepthincreasesprogressivelyagain.
ThisculturesystemispopularinsomeprovincesofChina,butproblemsarethesameaswithpondculture,pollutionhavingseriousimpactsontheenvironment.Thedevelopmentofthissystemshouldthereforebestrictlycontrolledandconfinedtoselectedareas.
5InshoreCageCulture
Inshorecagecultureisverypopularworld-wide,especiallyinAsia.Advantagesincludelowinvestmentandeasyroutinemanagement.Butthissystemisoneofthemainsourcesofinshorepollutionandthemaincauseforredtides.Ithasbeenreportedthat,inareaswhereinshorecagecultureiswelldeveloped,phosphoruscontentoftheseabottomis2000timeshigherthanthelegalvalueacceptedforenvironmentalprotection.Policymakershavebeguntonoticetheproblemsandtoissueregulationscontrollingthedevelopmentofthisculturalsystem,toprotectthenaturalenvironmentandtheaquacultureindustryitself.
Asmostfarmersusetrashfishtofeedculturedfishwithahighcommercialvalue,itdoesnottakelongbeforeagreatquantityoffaecesandfoodresiduesaccumulateontheseafloorandpollutetheentirearea.
Anotherproblemisthatfloatingcagescannotresiststrongwindsandwaves.Afteratyphoon,fewcagesarestillfunctionalandmanyofthefarmedanimalshaveescaped.Inthenearfuture,offshorecagecultureshouldbecomethemaincageculturesystem.
6OffshoreCageCulture
Chinaexperiencestyphoonsseasonally,especiallyinitssouthernregionsfromtheZhejiangProvincetotheHainanProvince.Eveniftyphoonsareonlyoccasionalinthenorthernregions,lossescanalsobeveryserious.
Traditionally,onlyfloatingcagesareusedininshorewaters.Duetopollutionandoverexploitationofthesewaters,fishcagefarmingshouldbemovedoffshore.AtpresenttherearetwotypesofoffshorecagesrecentlyintroducedintoChina.Onetypeisasinkablecage,theotherbeingaplasticgravitycage.
Researchersandfarmershavebeenencouragedtodesignnewmodelsofcageswhichwouldbeabletowithstandtyphoonsandstrongseacurrents.Inthenearfuture,offshorecagecultureshoulddeveloprapidly.
7ArtificialReefs
Anotherwayofsearanchingisusingartificialreefs.Thismethodwasexperimentedinthe1980sforfiveyears.Theoretically,itcontributestotheenrichmentoffisherynaturalresources.Butitssuccessdependsonmanyfactorssuchassiteselection,shapeoftheartificialreefs,desirablespeciesandotherenvironmentalconditions.Financialsupportisalsoimportantbecausereturnsoninvestmentsshouldbeconsideredonthelongtermonly.Thedevelopmentofthissystemhasbeenstopped.
8SeaRanchingandRestocking
Inthe1970s,DrC.K.Tsengpresentedaseriesoftalksandpublishedathesisentitled“Searanchingandseafarming”.Hedefined“ranching”asaculturesystemwhere“...atfirst,thecropisrearedinrestrictedareas,thenitsjuvenilesarereleasedintothenaturalenvironmentandfinallyitsadultsarefishedfromthisnaturalenvironment”.
Sincethe1970s,searanchingwastriedwithseveralspeciesinvarioussites.ShrimpofthespeciesPenaeuschinensiswererestockedonacommercialscale,especiallyinthelate1980sandearly1990s,attheannualrateofmorethanamilliardjuveniles.Duetounknownreasons,thisactivitywasstopped.Itwasobservedthatrecapturerateoftaggedshrimpdependedontheindividualsizeofstockedshrimpaswellasonthedurationandlocationoftherestockingprogramme.Tabulatedfiguresshowthatrecaptureratevariedgreatly.Thehighestratereached1.88percent,thelowestonly0.001percent.Itseemsthatsomeunknownfactorsinfluencerecapturealso.
Recapturerateforotherspecies,suchasabaloneandseacucumber,ismuchmorepredictablethanforshrimp.Accordingtodatarecordedfromcommercialcaptures,recapturerateforabalonemaybeashighas50to70percentifstockingsizeisgreaterthan30mm.Ifstockingsizeislessthan20mm,recapturerateisverylow.Forseacucumber,thisratedependsmoreonsiteselectionandimprovement,suchasincreasingshelteredareas.
Ingeneral,searanchingisagoodsystemtoenhanceortore-establishapopulationwhichhasdeclined,butnumerousfactorsinfluenceresults.Practically,atleastfourgroupsoffactorsshouldbetakenintoaccount:
-Speciesandnaturalpopulationcomposition
-Foodwebrelationshipsofstockedspecieswithnaturalpopulation
-Environmentalimprovement
-Factorsinfluencingrecapturerate,includingstockinglocation,durationofprogramme,sizeatstockingandpotentialpredators.
Resultsshowthatsearanchingisinitsinfancy.Thereisstillalongwaytogotoreachdesirablegoals.Cooperationinthisfieldshouldbestrengthenedandenlarged.
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