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FAQs

What is a shark?
Are there very many species of sharks?
Blue Shark.  Copyright 1998 Steve Drogin. Are sharks warm or cold blooded?
Do sharks blink?
Do sharks eat a lot?
What is the largest shark?
What is the smallest shark?
What is the fastest shark?
Are sharks vicious man-hunters?
Why do people hunt sharks?
How many rows of teeth do sharks have?
How long have there been sharks on the planet?
Why don't we find more shark fossils?

 

What is a shark?
A shark is a fish, and like other fish, it has a backbone, lives in water, and breathes through gills. Unlike other fish, a shark has a skeleton made of cartilage, the same material that makes up the end of your nose. Cartilage is strong, flexible, and lightweight.

 

Are there very many species of sharks?
Worldwide, there are over 350 species of sharks and 400 species of rays. Despite this diversity, you know when you're looking at a shark or a ray because their distinct body forms. Some adaptations enable sharks and rays to specialize in new ways of getting around, hunting, and feeding. These kinds of changes can increase the odds of survival, reproduction, and passing on those traits to the next generation, as well as enable species to use resources within a habitat differently, reducing competition.

 

Are sharks warm or cold blooded?
Most sharks are ectothermic (cold-blooded). Their inner body temperature matches the temperature of the water. However, some sharks, like the great white, can elevate their body temperature above that of their surroundings.

 

Do sharks blink?
Sharks don't blink. They have upper and lower eyelids, but these lids don't move and don't close over the eye. When biting prey, some sharks protect their eyes with a third eyelid called the nictitating membrane.

 

Do sharks eat a lot?
A shark eats about 2 percent of its body weight per day -- slightly less than a human eats. Because most are cold-blooded, they don't have to eat as much as a human eats. Some sharks can live for a year without eating, surviving on the oil stored in their livers.

 

What is the largest shark?
The largest shark is the whale shark. At over 45 feet, it's also the world's largest fish. The whale shark strains out tiny animals that drift in the sea, such as plankton, shrimp, and small fish.

 

What is the smallest shark?
The smallest shark is the spined pygmy shark. It's less than 10 inches long and can be found in the cold, deep oceans. It's bioluminescent which means it glows in the dark.

 

What is the fastest shark?
Most sharks are efficient swimmers. The highly streamlined mako has been clocked at speeds up to 22 mph.

 

Are sharks vicious man-hunters?
Sharks are highly-specialized predators, with sharp teeth, strong jaws, streamlined bodies, and powerful senses. However, sharks don't hunt humans -- their feeding strategies evolved well before humans entered the water. Even today, of the over 350 different shark species, fewer than ten are considered dangerous to humans.

There are almost six billion people on our planet, and less than ten people are killed by sharks each year. More sharks are killed by people -- over 12 million each year.

 

Why do people hunt sharks?
Sharks and shark by-products are important resources. Shark meat is high in protein, low in fat, and has no bones. Shark by-products can be found in many things we use everyday. One by-product, shark oil, is rich in vitamin A and is used in medicines, soap, cosmetics, and vitamins.

 

How many rows of teeth do sharks have?
Most sharks have 5 to 15 rows of teeth in each jaw. Unlike human teeth, shark teeth don't have roots to hold them in place, so their teeth are easily broken off. A tooth usually lasts about a week before it falls out. When this happens, the tooth behind it moves up to replace it. A new tooth can be replaced in as little as 24 hours. Sharks keep replacing their teeth all their lives. As the shark grows, its new teeth keep pace and grow larger than the ones that are replaced.

Bronze cast of a 14 million-year-old
Carcharocles megalodon tooth.
This tooth measures approximately 6 inches (15.5 cm) in length.
 

How long have there been sharks on the planet?
Sharks are some of the oldest and most successful vertebrates on the earth. The first sharks appeared in ancient oceans 400 million years ago.

 

Why don't we find more shark fossils?
Shark skeletons rarely fossilize. They are made of cartilage which decomposes so fast the tissue is not replaced by minerals. However, shark teeth are made of dentine and enamel and fossilize readily. A single shark may lose thousands of teeth in its lifetime. New sharp teeth replace old worn teeth which fall out and, sometimes, become fossils. Fossil teeth are often the only evidence of ancient sharks.

Blue Shark Photograph © Steve Drogin

Shark School | Kids' Habitat

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