a perpetual frown; and that mouthful of sharp, pointy 

 teeth have haunted more than one nightmare. But, it 

 all adds up to a vertebrate proficient in achieving its 

 sole objective — survival. 



One means of protection for the shark is its thick, 

 rough skin. It's rough because it has denticles, or 

 microscopic teeth, embedded in it. These unusual 

 structures are actually prototypes of the teeth found 

 in the shark's mouth, says Steve Ross of the N.C. 

 Division of Marine Fisheries in Morehead City. 



Whether a shark is escaping or pursuing, its 

 streamlined body, dorsal tail and assorted fins 

 maneuver it quickly through the water. As with most 

 fish, the fins move water across gill slits on the sides of 

 the shark's head, keeping a constant flow of oxygen 

 going into its body. 



For buoyancy, fish have an internal swim bladder 

 that changes amounts of air and gas according to 

 movements. Sharks, on the other hand, don't have a 

 swim bladder and must maintain buoyancy in two 

 other ways, says Ross. 



Sharks have a giant liver that is full of oil. Since oil 

 is lighter than water, the liver acts "kind of like a life 

 preserver," Ross says. 



Secondly, he says, most sharks constantly swim. 

 "As they move through the water, there's a lifting 

 force much like an airplane. The flow of water over 

 the body lifts them up." 



Because sharks must move all the time, there's no 

 sleep for most species. They don't really require sleep 

 anyway, says Lundie Spence, UNC Sea Grant's 

 education specialist. The shark's brain is so small, it 

 doesn't need resting. 



High on the list of priorities for the shark is eating. 

 To do so. it is equipped with "mechanisms" that help 

 it locate food and with a set of teeth that would scare 

 off any dentist. 



Those mechanisms, or sensory organs, are very 



Scientist Carl Luer continues to study the anatomy 

 of sharks. 



well-developed, says Ross. Sharks have an acute 

 ability to detect low-frequency vibrations such as 

 those set off by a struggling fish. They also can smell 

 objects long distances away with nostrils located un- 

 derneath their head. This combination allows sharks 

 to quickly home in on their prey. 



For years, it was believed that the glassy eyes of a 

 shark could only see blurry, mottled shapes. But 

 research shows that sharks can discern color and fairly 

 definite shapes — a handy feature around mealtime. 



Carnivorous sharks tear into their dinner with up to 

 1,000 sharp, white teeth. Ross says each species has a 

 set number it can replace indefinitely. A few have no 

 teeth at all. 



Each year, more people die of bee 

 stings than from shark attacks. 



Sharks lose their teeth easily and frequently. White 

 sharks, for example, may lose a few each time they 

 eat, says Ross. When that happens, they have another 

 tooth, or even a whole set, folded back under their 

 jaw, ready for the next meal. 



A shark's diet depends on its size and species, says 

 Ross. Some eat fish, while others, like the dogfish, eat 

 crabs. We know of a few that eat mammals. The great 

 white eats seals and penguins, Ross says. The 

 toothless species, like the basking and whale sharks, 

 eat plankton. 



Their digestive system, as their nervous system, is 

 relatively primitive. Neither have changed much over 

 the years. Another primitive facet of the shark is the 

 high concentration of salts and minerals found in its 

 blood, says Spence. The shark urea stores a large 

 quantity of salt in the shark's body, which prevents it 

 from dehydrating quickly. 



With all this finely-tuned survival equipment, 

 sharks can live 20 or 30 years. Their most vulnerable 

 stage in life, however, is the first. 



Sharks reproduce in three ways that vary with the 

 species. Some females lay eggs on the ocean floor. 

 Others produce eggs surrounded with a yolk sac that 

 provides nutrients to the embryo as it develops. And 

 some form eggs that attach to the womb and derive 

 nutrients from it. 



The majority of sharks are born by the second and 

 third methods, which produce young, or pups, in the 

 womb. With the third type of reproduction, says 

 Spence, usually only the first-developed embryo lives 

 because it eats the others that later enter the womb. 



From conception to death, the shark attempts to 

 satisfy its voracious appetite. But fortunately for us, 

 its affinities are toward fish and not flesh. 



— Sarah Friday 



