Imagine you were out on the sea with your speedboat. Then a fin comes up right beside your boat. You are sure it is a dolphin because no one can swim as fast as this animal. After a couple of seconds the creature jumps out of the water extremely high. Now you can see the rest of its body and you slowly recognizeÖa shark!
Sharks are good swimmers; they can reach a speed up to 40 mph. The maco shark is the fastest. For a short distance it can reach up to 60 mph. This shark is also a good jumper. It jumps about 6.5 yards high out of the water.
One of the Oldest Creatures on Earth
100 million years before the dinosaur age sharks already swam through the oceans. The oldest shark lived about 400 million years ago. Since 60 million years ago, there are some shark families which didnít change very much if you compare them to sharks today.
Different Kinds and Their Treats
One shark is not like another shark. In all we know about 360 kinds of sharks. Half of those live on the bottom of the sea and they never come near a human. The others live near the surface of the oceans. Sharks have all different kinds of shapes and sizes. There are sharks only 6 inches long and others which are 15 yards long. The biggest sharks are mostly the most peaceful sharks. For example, the whale shark or the giant shark only eats plankton and tiny crabs. Other sharks eat only little fish, crabs, mussels, sea stars, and other little sea creatures. Very dangerous sharks are the blue, Greenland, riff, hammerhead, and great white or mako sharks. They can eat seals, sea lions, sea elephants, and even polar bears.
Why Donít They Sink?
Sharks donít have a swim bladder, an organ filled with gas, which allows fish to float and not sink. Instead sharks have a special skeleton made out of cartilage. Cartilage is less heavy than the material of normal bones which makes it easier for them to float. Sharks also have a kind of light oil in their liver which helps them not to sink.
Sharks Could Drown!
Did you know that sharks could drown? Some kinds of sharks have to swim permanently. Only then they can get oxygen because water is flowing through their grills. Otherwise, if they are trapped in a net or in a small cage, they die. Other sharks donít have this problem because they can press the water through their gills.
Sharks donít have a family life. They live alone, they hunt alone, and they donít take care of their babies. They are loners. Only for reproduction, some sharks meet in large groups. Other sharks find each other as a couple because the female gives off a scent.
Sharks give birth in three different ways. Some sharks, like the cat shark or bull shark, lay eggs. The eggs look like squares. On each of the four corners there are strings which tie them up between water plants until the baby sharks are ready to leave. Other sharks, like the blue shark, the hammerhead shark, the gray shark, or the saw shark, give birth to their babies. Then there is another way, which is between laying eggs and giving birth. Sharks like the whale shark, the white shark, the tiger shark or the carpet shark hold their eggs inside their body. If the babies are ready, they come out of the eggsí hard shells but inside the body of their mother. Right after that, the mother gives birth to the babies.
The pregnancy of a shark can take very long. For a gray shark it takes a little bit longer than one year and for a curl shark even two years. The reason for these long periods is to have a strong and complete baby that has a good chance to survive.
Some baby sharks donít like their brothers and sisters. From the sixty babies of a tiger shark often there are only two left. The babies eat each other up if they donít have enough food. To make sure that they donít do this, some sharks developed separate rooms for each baby in the motherís body, so they canít hurt or kill each other.
Sharks donít take care of their babies. They have to be on their own. They donít learn from their parents how to hunt, how to avoid enemies, or how to reproduce. All these they know by instinct. They have to be grown-ups right after their birth to survive.
If they arenít eaten by enemies or die because of an illness, sharks can live for a time long, but the life expectancy is different depending on the type of shark. The cat shark, for example, can live 8 years, the Dornshark can live 24 years, the other sharks can live as long as 30 to 50 years. The record for a shark life we know was 70 years.
A Shark Doesnít Know Toothache
The most important tool of a shark is his teeth. If you ask somebody who lived through a shark attack, he or she would tell you that the bite didnít hurt much. You think that is really unusual, but the teeth of a shark are razor sharp, as hard as steel, and on the surface of one tooth are little teeth like on a saw. It can cut even thick bones very easily and fast.
We could be jealous at the teeth of a shark. It doesnít know toothache. The teeth of a shark grow in an extra layer of skin where the shark doesnít feel pain. While cutting a bone, a tooth might break or get lost, but for a shark it doesnít matter. After the first row of teeth, there can grow up to five more rows of teeth. In a few hours the broken or lost tooth is renewed. In its special layer of skin, the new teeth always grow again. The tiger shark, for example, uses up to 1,400 teeth in 10 years. The riff shark, which often bites into big rocks searching for hidden food, uses even up to 10,000 teeth in 18 years. The lemon shark changes its teeth once a week even if they are not broken.
Many sharks have not only teeth in their mouth but also tiny teeth on their skin. The skin teeth are the original teeth and they are kept from the past. Scientists researched on embryos of sharks that the teeth in the mouth develop from the skin teeth during the pregnancy. The skin teeth work like sandpaper. If a shark passes by and touches you, it can rub your skin until it is bleeding. Often the blood raises the appetite of the shark.
Humans normally have five senses: seeing, hearing, touching, taste, and smell. Sharks also have these senses but they work differently. The sight of a shark is not very good. The sunlight doesnít come through the water very deep, so the eye of a shark only works for a short distance.
Usually a shark uses its ears to notice things at a bigger distance. The shark has not only two ears on its head, its ears are two long lines from the beginning of its head to the tip of its tail fin. These long lines have little holes where water floats in. The shark can hear different waves of sound in the water like we can hear different waves of sound in the air. Every movement makes sound, but not everybody can hear it. The movement under water makes very deep sound waves. These sound waves are not hearable for humans but they are for sharks. They can spot their prey with their ears in the distance. If the shark comes closer, its eyes and nose take over. A shark attacks if it hears fidgety movement, if it sees its prey, and often if it can smell fresh blood.
A shark has two noses, on each side of its head. These noses also have two holes. Through the one hole the water gets in and through the other it gets out. The water floats permanently through the nose, so the shark can recognize every change. A sharkís nose is extremely good. For example, the great white shark can smell one single drop of blood in a full bathtub of water.
If a shark isnít sure its prey tastes good or not he uses its fourth sense, taste. Instead of a tongue the shark uses its whole body to test the taste of its prey. The cells of taste are spread out over the whole skin. Touching the shark can prove if the prey is good or not.
If one shark attacks it practically calls other sharks with the smell of fresh blood in the water. Up to twenty other sharks can come, and a wild eating frenzy begins. Now the sharks eat whatever they can find and it doesnít matter if its eatable or not. They not only bite into their prey but also into boxes, cable, rocks, or boats, but in this situation they never hurt or kill each other.
Even if the water is cloudy because of blood and they cannot see each other, their fifth sense comes alive. This sense is an electrical sense. The whole head of a shark has tiny holes. In each hole is a little hair, which can get electrical signals up to a distance of one yard. All animals send out electrical signals, for example, through muscle movements. If a shark recognizes these electrical signals from other sharks during a wild eating frenzy, it knows that it is not allowed to bite.
Friends and Enemies
Believe it or not, sharks have friends. Sharks often have companions. These are, for example, pilot fish. The pilot fish is not interested in the leftovers of the sharkís prey. They eat fish lice, little crabs, and blood sucking worms, which live on the skin of a shark. So pilot fish clean "their" shark and as a reward the shark wonít eat them. The shark also protects the pilot fish from most of their enemies because they avoid sharks. The friendship between the shark and other fish work in the same way. Some fish suck on the shark and clean their skin. Therefore the shark takes it on his journey. All together we know almost 10 different kinds of fish which live in such a relationship with a shark.
The relationship between sharks and dolphins has two sides. On the one hand, they can live and hunt together peacefully. On the other hand, sometimes sharks attack lonely dolphins and sometimes dolphins in a group attack sharks. With their hard and pointed head, the dolphins ram into the smooth belly or the gills of the shark and hurt it. The shark can die because of these injuries.
Sharks are dangerous, but they are not the kings of the oceans. They have a lot of enemies. The whales, often much bigger than the sharks, are one of their enemies. Killer whales or pod whales can swallow a whole shark. Also a huge octopus can be dangerous for a shark. With its 9 to 13 yard-long arms, they catch the sharks and eat them up.
Other animals like the swordfish or a sea lion also can hurt a shark very seriously. Sea snakes are very dangerous. They have a very strong poison, which kills other animals immediately. Therefore, a shark avoids sea snakes.
There are even sharks which eat other sharks, especially the gray shark which eats all sharks which are smaller than three yards. Also the great white shark eats everything which is smaller than itself.
The most dangerous enemy of the sharks, like with many other animals, is the human. Fishermen catch sharks for their flesh, their skin, and some special parts of the body. The flesh is used as food, the skin as leather, and some parts of the body are very rich in vitamins, so they are used for medicine.
Many people think that sharks are beasts which should be killed. It is true that sometimes sharks attack people, but more people die from lightning, snakebites, or bee or wasp stings, not even to include car accidents. Nobody, though, thinks that we have to forbid cars. People kill sharks because of hate, to protect the beaches, or because they think it is a nice sport.
Actually people kill 4.5 million sharks in one year. It would be the same if the sharks would kill half of the people who are living in Michigan in one year. So the population of sharks is decreased worldwide. In the last 10 years some countries have tried to protect sharks. Now there is a limited number of sharks that we are allowed to kill. Even though they started to protect sharks, many of them are still endangered today.
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Carcharodon, Carcharias. Great White Shark. Enchanted Learning Softwarehttp://www.enchantedlearning.com/subjects/sharks/species/ Greatwhite.shtml last visited: 11/30/01