SHARKS

SEYMOUR SIM;O.N
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SHARKS

SEYMOUR SIMON
SCHOLASTIC INC.
New York Toronto London Auckland Sydney
it never fails. You're at the ocean, swimming in the surf, and someone pretends to

be a shark. They sing ominous music and then lunge at you.

People have always made up myths and legends about creatures they find

mysterious and terrifying. Sensationalized books, television shows, and movies

strengthen the myth that sharks are always on the lookout to attack people. The

truth is that there are only about a dozen shark attacks in the United States each

year (about 100 worldwide), and most victims live to tell their stories. In fact, you
have a better chance of being hit by lightning than of being attacked by a shark.

Sharks have killed fewer people in the United States in the past one hundred years

than are killed in automobile accidents over a single holiday weekend. And no
shark in the world counts people as part of its regular dinner menu.

When you know the truth about sharks, you'll begin to see them as the fasci-

nating creatures they are, instead of the monsters of myth.

 Sharks are fish, but they are very different from most fish. They belong to a

class of fish known as Chondrichthyes (kon-DRlK-thees). The name comes from

the Greek words chondros, which means cartilage, and ichthyus, which means fish.

Like all fish, sharks have backbones, but unlike other fish, sharks have no other

bones. Their skeletons are made of cartilage, a tough, white, flexible material, just

like the stuff at the end of your nose and in your ears.

Sharks breathe through gills like most fish, but they have five to seven pairs of

gill openings instead of the usual one, as you can see on this Caribbean reef shark.

Most fish don't have eyelids, but some kinds of sharks have three of them for each

eye. Two are like yours, an upper and lower eyelid. The third eyelid is transparent.

It covers the entire eye and protects it.

Sharks also lack the swim bladder that keeps most bony fish afloat. A swim
bladder is like a balloon inside a fish's body that keeps it buoyant. Sharks keep

from sinking because there is oil in their livers that acts like a float, and also be-

cause they keep swimming. If a shark stops swimming, its weight pulls it down to

the bottom. Scientists calculate that sharks cruise at about one to three miles per

hour. A few kinds can suddenly speed through the water at up to 60 miles per

hour.
 Most people think of jaws and teeth when they think of

sharks, and with good reason. Many sharks do have pow-

erful jaws and rows of sharp teeth. Some sharks can bite

nearly 300 times harder than a human, enough to cut

through a thick piece of steel. Sharks may lose a tooth

when they bite something hard, but they never run out of

new teeth. A shark's jaw is lined with as many as twenty

rows of teeth, one behind the other. When a shark breaks

or loses a tooth, another one moves forward to replace it.

Some sharks replace their teeth one by one, while others

replace an entire row at the same time. A shark may go

through thousands of teeth during its life.

The sand tiger shark, shown here, is common in North

American waters. It will eat anything it can swallow,

including bits of food, car license plates, and cans of

paint. Its nickname is the garbage-can shark. But with its

strong, sharp teeth it will also attack other sharks, sea

turtles, rays, seabirds, and even the occasional human

being.
 No two kinds of sharks have exactly the same kind of teeth. Bottom-dwelling

sharks, such as the nurse shark, usually have broad, flat teeth for crushing crabs

and other shellfish. Fast-swimming sharks, such as the mako and great white, who
hunt in the open sea, have sharp teeth for cutting up other sharks, marine

mammals, and big fish. But with all these teeth, sharks don't chew their food. If

the prey is small enough, a shark swallows it whole. If the prey is too big, a shark

uses its teeth to tear it apart and then swallows the parts.

Three of the largest sharks in the world have the smallest teeth compared to

their body size. The whale shark (shown here), basking shark, and megamouth
shark are called filter-feeders. They swim near the surface with their mouths

open. As the water flows through their gills, they strain out small animals called

plankton. These sharks have hundreds of tiny teeth, each smaller than the

thickness of a pencil.

Even a shark's skin has teeth! A shark's body is covered with rough skin that

feels like sandpaper and is covered with little skin-teeth called denticles

(DENT-uh-culs). You can cut yourself by rubbing against a shark's skin.

 All sharks are cold-blooded. This means that the temperature of a shark's body
depends upon the temperature of the water around it. Most sharks live in temper-

ate or tropical ocean waters, while only some inhabit the colder polar seas. One
way scientists classify sharks is by the temperature of the water in which they live.

Different kinds of sharks are adapted to different temperatures, so as the water

temperature changes with the seasons, many sharks migrate. For example, sharks

that live in the Northern Hemisphere may travel farther north in the summer to

find cooler water and travel south toward warmer water in the winter.

Some sharks travel great distances. One blue shark (like the one shown here)

was tagged in the waters off New York City and then found months later off the

coast of Brazil, 3,700 miles away.

 A shark's six (yes, six!) senses make it one of the best hunters in the world.

Because sound travels five times faster and farther in water than on land, hear-

ing is the first sense that alerts a shark to its prey. Sharks have two inner ears,

which are sensitive to low-frequency sounds. They can hear a wounded fish

thrashing in the water from as much as 3,000 feet away.

As the shark swims toward the sound, it may come across an odor path that

flows in a current from the prey. Sharks are like "swimming noses," and can detect

even tiny amounts of blood in the water. The shark's ability to smell seems to in-

crease as it gets hungrier. Reef sharks that had been deprived of food in experi-

ments were able to smell as little as one drop of fish blood in a large tankful of

water. Given this, it's not so surprising to learn that half of a shark's brain is de-

voted to its sense of smell.

Beneath the ocean's surface it is not easy to see, since the water is often cloudy

and dim. But a shark's eyes are well suited to this underwater world. In the back of

a shark's eye is a mirrorlike surface called a tapetum lucidum. The tapetum re-

flects light back through the eye and helps the shark to see in dim light. Light

bouncing off the tapetum makes some sharks' eyes seem to glow in the dark, like

cats' eyes, as you can see with this tiger shark.

 Sharks have two kinds of touch that aid them in locating prey. One kind

is like the sense of touch you have when you feel whether something is hot

or cold or rough or smooth. The shark also uses a kind of "distant" touch.

This distant touch allows the shark to sense the vibrations of an object long

before it comes into contact with it. The blacktip reef shark pictured here

could have tracked the mackerel from as much as 600 feet away, by sensing
its vibrations.

The shark's ability to do this comes from its lateral lines, rows of small

holes that run along the shark's sides, stretching from its head to its tail.

When a fish swims nearby, it causes small movements in the water. The
shark's lateral lines sense the movement, and the shark can find the fish, even

if it cannot see it.

Some sharks can even use an extra "sixth" sense, called electroreception,

to locate prey they cannot find with their other senses. Sharks have hun-

dreds of tiny pores in their heads and lower jaws called the ampullae of

Lorenzini. (Lorenzini was the name of the 17th-century scientist who first

described them.) The shark's ampullae pick up the small electrical signals

that all living animals give off. The electrical signals guide the shark to its

prey at close range. Sharks have the most sensitive electrical organs of any

known animal.
 Many bony fish reproduce through external fertiliza-

tion. The female fish deposits many small eggs in the water,

which are then fertilized by the male. Unlike most bony

fish, all sharks reproduce through internal fertilization, as

mammals and birds and reptiles do. However, once the

eggs are fertilized inside the female shark, they develop in

several different ways, depending on the species of shark.

Some sharks, such as horn sharks, nurse sharks, and cat

sharks, lay their fertilized eggs on the ocean floor. Each

egg is enclosed in a case or shell just before it is laid, and
the case becomes attached to rocks or seaweed. Horn
sharks screw their egg cases into cracks between rocks or

sunken pieces of wood. When the eggs are first laid, they
are soft and pale. The cases harden in a few hours into

tough, leathery shells, which protect the developing eggs.

The photograph shows a swell shark emerging from its

egg case. The six-inch-long baby shark, or pup, took

about eight months to hatch. Shark pups hatch in six to

hfteen months, depending on the species. Sharks that lay

eggs are called oviparous.

 Most kinds of sharks keep the developing eggs inside their bodies and then

give birth to live young. Each shark lives off a yolk until it is ready to hatch. In

one kind of shark the developing young are cannibals, feeding first on yolks, and

then on one another. The female sand tiger shark has a double uterus, and, by the

time the pups are ready to be born, there will be only two pups left —one in the

female's right uterus, the other in the left. Sharks that give birth to live young
from eggs that have developed in their bodies, including the tiger, mako, and

thresher sharks, are called ovoviviparous.

In a few kinds of sharks, such as the lemon, hammerhead, and blue, each fertil-

ized egg develops separately inside a small egg sac. The pups receive food and

oxygen from the mother through an umbilical cord. The young sharks are born

live in litters ranging from two to twenty. The photo shows the birth of a lemon

shark. The tail of the pup is still wrapped in the egg sac. Sharks that give birth in

this fashion are called viviparous.

Newborn pups make easy prey for other sharks, so female sharks go to areas

where sharks don't usually live to give birth. The mother might be tempted to eat

her own pups, but she is inhibited from eating during the birthing period. This

is the extent of the mother's nurturing though,- sharks don't care for their young
after birth.
 There are about 350 kinds of sharks, which seems like a

lot until you learn that there are more than 20,000 kinds of

bony fish. Researchers think that there may be other kinds

of sharks not yet discovered.

Sharks come in many different sizes, shapes, and colors.

The dwarf shark is as small as your hand, while the whale

shark is longer than a school bus. Most sharks have slen-

der, torpedo-shaped bodies and long, pointed snouts. But

some sharks have short, broad snouts and tails, and others

have very flat bodies and fins. There are brown sharks and
blue sharks and sharks with polka dots like this cat shark.

Some have strange-looking heads, and others have

strange-looking tails.
-I.
 The largest shark, and indeed the largest fish in the

world, is the whale shark. It can grow as long as sixty feet

and weigh as much as twenty tons — as long and heavy as a

huge trailer truck. Its tail measures ten feet from top to

bottom — that's as tall as the height at which a basketball

hoop is mounted. Despite its size, the whale shark is

harmless to humans. In fact, scuba divers sometimes hitch

a free ride on the shark's back or by holding on to one of

its fins.

The whale shark is like a whale in more ways than its

size. Like some of the largest whales, the whale shark is a

filter feeder. This giant water strainer opens its six-foot-

wide mouth and filters plankton and even entire schools of

small fish from thousands of tons of seawater each hour.

Whale sharks live in both tropical and temperate ocean

waters, usually far out at sea. They usually swim alone, but

some groups of up to a dozen whale sharks swimming to-

gether have been sighted.

 /

The hammerhead shark is one of the most unusual-looking fish in the sea. Its

wide, flattened snout really does look like the head of a hammer. Its eyes and nos-

trils are at the outermost tips of the hammerhead. By swinging its head back and

forth as it swims, a hammerhead gets a wide view of its surroundings.

There are about nine different kinds of hammerheads, ranging in length from

four feet to twenty feet. Several of the largest kinds, including the scalloped

hammerhead, the smooth hammerhead, and the great hammerhead, are fairly

common in North American waters. These large hammerheads are dangerous

hunters but live mainly in offshore coastal waters and feed on fish, including other

sharks. Sometimes hammerheads come into shallow waters to feed and have been

known to attack humans when they do.

Most hammerheads are solitary swimmers. But scalloped hammerheads (shown

here) often swim in groups of up to one hundred sharks. Scientists are not sure

why they do this. Hammerheads have few natural enemies, so protection doesn't

seem to be a good explanation for this behavior. Perhaps they gather together

because of abundant food in the area or for reproductive purposes.

 Probably the best known of all sharks is the great white shark. It is the third

largest shark, but the most dangerous. In the movie Jaws, the great white was pic-

tured as a fierce, intelligent, and unpredictable human-eating monster. But "human

biting" is probably more accurate, because only rarely does a great white — or any

other shark — actually eat people.

When it does attack humans, the great white shark probably mistakes the

swimmer for a sea lion or seal, its favorite food. After a bite or two the shark dis-

covers the person isn't a seal, and swims away. This isn't to say that the great

white isn't dangerous. Even a single bite can cause great loss of blood, shock, and

death. The jaws of a great white shark are filled with fifty two-and-one-half-inch

pointed teeth — the largest teeth of any shark. Narrow teeth on the bottom jaw

hold the prey, while the saw-edged teeth on top cut it into bite-sized chunks.

Unlike most fish and many sharks, the great white is warm-bodied —which is

not the same as warm-blooded. The great white has a body temperature as much
as ten degrees Fahrenheit warmer than the surrounding water. This warmer body

temperature means more energy so the shark can swim faster and catch its prey

more easily.
 Sharks don't attack people very often, but by following a few simple rules you

can reduce your risk of an attack even further.

Don't swim in water when sharks have been seen, especially in places where

garbage or wastes are dumped. Sharks often stay in an area for several weeks.

Always swim with another person or in a group. Sharks are more likely to

attack lone swimmers.

If you have a cut, stay out of the water until it stops bleeding.

Sharks are more likely to attack bright or shiny objects, so it's probably wise

to remove jewelry before you go swimming.

If you do see a shark, don't panic. The more you splash around, the more

interested the shark will be in you. Tuck your arms and legs toward your

body and try to keep still.

Sharks have been swimming the oceans for longer than people have even ex-

isted. The earliest known sharks lived more than 400 million years ago. That was

200 million years before the first dinosaurs. Rather than thinking of sharks as

monsters to be destroyed, we can learn to appreciate their interesting lives. If we

understand their behavior, we can avoid most dangerous encounters and live in

harmony with these most awesome fish.

 The storm shall not wake thee, nor shark overtake thee,

Asleep in the arms oj the slow-swinging seas.

—RUDYARD KIPLING

Photo credits: cover: © David B. Fleetham, pg. 1: © Michael Nolan / Innerspace Visions, pp
2-3, 19 © Mark Conlin, pg.4 © 1988 Doug Perrine, pp. 7, 8, 23, 32, © Norbert Wu, pg. II:

© Ron and Valerie Taylor, pg 12: © Mike Nolan, pp © Doug Perrine, pg 16: © 1979
15, 20:

Tom McHugh, the Natrona! Audubon Society Collection, pg. 24: © Doc White/Images
Unlimited, Inc , pg. 27: © James D Watt/innerspace Visions, pg 28: Rosemary Chastney/
Ocean Images, Inc, pg. 31: © Ocean Images/Al Ciddings

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transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise,
without written permission of the publisher For information regarding permission, write to HarperTrophy,
a division of HarperCollins Children's Books, a division of HarperCollins Publishers, 10 East 53rd Street,
New York, NY 10022.
ISBN 0-590-76780-1
Copyright © 1995 by Seymour Simon.

All rights reserved. Published by Scholastic Inc., 555 Broadway, New York, NY 10012, by arrangement ^

with HarperTrophy, a division of HarperCollins Children's Books, a division of HarperCollins Publishers.

SCHOLASTIC and associated logos are trademarks and/or registered trademarks of Scholastic Inc.

18 19 20 5 6/0
Printed in the U.S.A.
First Scholastic printing, November 1997 08
Typography by Elynn Cohen
 TiAC K
YOU K
There are over 350 different kinds of sharics.
Sitarics can travel great distances—up to tiiousands of miles!
Some sharks will eat anything they can swallow— including
bits of garbage, license plates, and even paint cans*
You have a better chance of being hit by lightning than of
being attacked by a shark.

LEARN E OW—AND MORE—

ABOUT THESE FASCINATING DEMONS OF THE DEEP
u Combines seamless description with excellent photos to describe
creatures that never fail to fascinate." S€hool Library Journal

vwwww
the author of over 100 highly acclaimed science books for
is
young readers, including whales, big cats, snakes, and wolves*

This Schola^tK edition is only

available for distribution through

the school market.

SCHOLASTIC INC.
Cover photo Sandbar shark ''J David B Fleelham
1
1^40-76780- 1 RI.3 007-010