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Sharks• Class Chrondrichthyes
-cartilaginous skeleton• All are carnivorous• Poikilotherms• Rough, thick skin, Placoid
scales• Elongated body• Countershading• Have no swim bladder, must
swim to keep from sinking• Specialized sensory system
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Shark Diversity• Of 300 species
known…• Only 10 attack man• Found in all ocean
environments• Efficient predators• Range in size from 4”
to 30’• Long fossil record,
over 450 million years
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Shark Feeding Mechanisms
• Jaws and teeth– All are carnivorous,
feeding on plankton to meat
– Pelagic and some benthic
• Lateral line system– Aids in prey location
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Shark Vision
• Rods and cones• Moving lens for
close-up viewing• Reflective layer
behind retina--dim objects (tatum lucidum)
• Protective membrane covering eye
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Shark ReproductionShark Reproduction• Internal fertilization• Two ways to bear
young:– Oviporous
• Spotted dogfish• Whale shark
– Ovoviviporous• Mako, thresher, sand-
tiger: babies cannibalize• Hammerhead: up to forty
to fifty pups
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More Shark Adaptations• Electroreception in
Sharks– Lateral line-extensive in
most sharks– Cephalic canal: head
region– Ampulae ofLorenzini:
pores in head that detect temperature and electric fields
• Shark Bouyancy– Lack swim bladder– Heterocercal tail– Oily livers– Cartilage– Pectoral fins
• Osmoregulation– Urea in bloodstream, with
special adaptation to prevent toxicity
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Shark Attacks?• Shark attacks
– Typically 50 per year in US, 100 worldwide are reported
– 2001, The Summer of the Sharks?
• What to do:– Watch out and get out– Nets, aerial spotters– Bang sticks– Blow to head, gouge eyes (?)
• Shark stocks– Low reproductive
rate– Easily overfished– Highly restricted
fisheries