FAQ's About Sharks
Frequently Asked Questions about Sharks
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 spine 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.
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.
Is a shark a fish?
Yes. There are basically three kinds of fishes alive today—the primitive jawless fishes (hagfishes and lampreys), the cartilaginous fishes (sharks, skates and rays) and the bony fishes, which includes most of the living species of fishes.
Sharks evolved from fishes with bony skeletons, but now sharks have skeletons made of cartilage (the same material as the tips of our noses). Lacking swim bladders, which most bony fishes use to regulate buoyancy, they may have lost bone as one means of achieving more neutral buoyancy. Instead of a swim bladder, sharks have large, oil-filled livers that give them buoyancy.
Because they have cartilaginous skeletons, sharks do not fossilize well—except for their teeth. Sharks shed their teeth throughout their lives, so fossil shark teeth are common in some places. People collect a lot of fossil shark teeth near Scotts Valley, California; Bakersfield, California; and Venice, Florida.
Scientists think that having their nostrils separated helps hammerheads to better follow the direction of a scent trail. A hammerhead can detect a slight change in the concentration of a scent between the two nostrils. The shark's Electro receptor organs are also widely spread, perhaps increasing their sensitivity. And their eyes sit out on the ends of their head, giving them extremely good binocular vision.
In addition, most sharks use the underside of the head, as well as the pectoral fins, to help them "fly" through the water. It is possible that the broadened head also provides additional lift.
Can sharks hear?
Sharks and other cartilaginous fishes are able to hear sounds in the water. They hear best in low frequency ranges below 1,000 Hz, the range of most of the natural sounds under water. No cartilaginous fishes are known to produce sound, as is the case in many bony fishes. A shark's lateral line system, like that in other fishes, can detect nearby mechanical vibrations and sounds, as well
Can sharks sense electrical currents?
Yes, scientists have found that sharks have the keenest electric sense yet discovered. Sharks have a system of electro receptors—special sense organs located in tiny pits in the shark's skin. These electro receptors can detect electrical currents and changes in their intensity—as small as thirteen-billionths of a volt per inch. Since all living creatures produce a weak electrical field, the electric sense can help sharks locate prey.
How do deep-sea sharks see in the dark?
There is some light in the deep sea, where many animals are bioluminescent. But most deep-sea sharks don't see well and probably rely heavily on their other senses: smell, vibration and electro reception.
The exception is the deep-sea catshark. Catsharks are well adapted for seeing in dim light. They have big, well-developed eyes with large numbers of light-gathering cells. In addition, in the back of their eyes, catsharks have a reflective surface, called a tapetum lucidum, which helps concentrate dim light. Catsharks, unlike other sharks, can also adjust the size of their pupil.
Catsharks get their name from the similarities between their eyes and the eyes of cats, which hunt in the dark on land.
Which shark is the largest?
The largest shark is the whale shark, which can grow to about 70 feet (21.3 meters) long. Whale sharks live in shallow water in the tropics and near-tropics around the world. These giant sharks swim close to the surface, and open their mouths wide to feed. But they don't eat fish (or any other big prey). The largest shark in the world feeds on microscopic plankton—primarily small, shrimp like crustaceans called copepods—which it filters out of the water. Feeding whale sharks look a lot like huge vacuum cleaners swimming along just below the surface.
How large do great white sharks get?
The longest great white sharks accurately measured range from 19 to 23 feet (5.8 to 7 meters). A 21 foot (6.4-meter) white shark was estimated at 7,000 pounds (3,175 kilograms). Great white sharks eat fishes until they reach large size, and then they switch to seals, sea lions and other marine mammals while continuing to eat some fishes. No one knows how long white sharks live, but 20 years may well be a conservative estimate.