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Typeofsharks.doc

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Typeofsharks Thereareatleast350speciesofsharkrangingfromthesmallest,thepygmyribbontailcatshark(8to10incheslong)tothelargest,thewhaleshark(upto45feetlong). Sharksareequippedwithaspecialsetofsensors,arrangedinclustersovertheirheads,thatcanpickupelectromagneticcurrentsemittedfromotheranimals.Sharkshavebadeyesight,butthesesensorshelpdetectpreyfrom1to3yardsaway.SharkscanalsodetecttheelectromagneticfieldsoftheEarthandmayusethisabilitytoguidethemduringmigration. Sharksareoftenthoughtofascold-bloodedkillersthatpreyonhumans.However,only32specieshavebeenknowntoattackhumans,andmostattacksareaccidents.Often,sharksinhabitthesameshallow,warm-waterareasashumans.Thesharkmaymistakeapersonstandingorfloatinginwaterfornaturalprey.Thesharkgoesinforthekillbut,afteronetaste,usuallygivesuptheattack. Manysharkattacksinvolvepeopletryingtofreesharksfromfishingnets.Sharksalsoareterritorialanimalsandmayattackiftheyfeelthreatened.Thechancesofbeingattackedbyasharkareverysmall,andthechancesofdyingfromasharkattackhavegreatlydecreasedovertheyears.Infact,intheUnitedStates,apersonis30timesmorelikelytobekilledbylightningthanbyashark.Dogbitesare1,000timesmorecommonthansharkbites. Sharksarefishedfortheirfinsandcartilage.Shark-finsoupisapopularfoodinsomeareas.Afterthefiniscutoff,therestofthesharkisdiscarded.Sharkcartilageisasubjectofmuchscientificstudybecausemedicinemadefromitmaystopthegrowthoftumors.Sharkcartilageissoldinpillformasanalternativemedicine.Sharkfinningandfishingforcartilagehavecausedadeclineinpopulationsinsomeareasoftheworld.Sharksmatureandreproduceslowly,soitisdifficultforthemtoreboundfromadecline. Greatwhiteshark:BestknownfromthemovieJaws,thegreatwhiteisalarge,heavy-bodiedshark,about20feetlong,withlargebladeliketeeth.Widelythemost-fearedofsharks,greatwhiteattacksarerare,andmostscientistsagreethatitsreputationisundeserved.Manyscientistsbelieveitisendangeredduetosportfishingandshrinkingfoodsupplies. Whaleshark:Reachinglengthsofupto50feet,thewhalesharkisthelargestfishonearth.Thisgentlegiant