SharksareamongtheoldestanimalsonEarth.Therearehundredsofkindsofsharks.Mostareabouttwometerslong.Thedogfishshark,however,islessthantwentycentimetersinlength.Asharkhasanextremelygoodsenseofsmell.Itcanfindsmallamountsofsubstancesinwater,suchasblood,bodyliquidsandchemicalsproducedbyanimals.71Sharkseatfish,othersharks,andplantsthatliveintheocean.
Sharksgrowslowly.Aboutfortypercentofallsharkslayeggs.72Somesharkscarrytheiryounginsidetheirbodiesashumansdo.Somesharksarenotabletoreproduceuntiltheyaretwentyyearsold．Mostreproduceonlyeverytwoyears.Andtheygivebirthtofewerthantenyoungsharks.Forthisreason,over-fishingofsharksisofspecialdangertothefutureoftheanimal.
Sharksareimportantfortheworld’soceans.Theyeatinjuredanddiseasedfish.Theirhuntingactivitiesmeanthatthenumbersofotherfishinoceanwatersdonotbecometoogreat.73.
Peoplehuntsharksforsport,food,medicineandtheirskin.Expertssaytheinternationalmarketforsomekindsofsharkshasincreasedbecausemanypartsofasharkarevaluable.
Collectorspaythousandsofdollarsforthejawsofashark.74Theskinofasharkcanbeusedlikeleather.
InAsia,peopleenjoyakindofsoupmadefromsharkfins.Expertssayafishermancanearnalotofmoneyforevenonekilogramofsharkfins.SharksareamongtheoldestanimalsonEarth,butsomesharksareindangerofdisappearingfromEarth.75.