Discovery Channel

A great white shark comes out of the water off the coast of South Africa in the new special "Air Jaws: Fin of Fury," one of the new specials in this year's Shark Week lineup.

(Chris Fallows)

Don't go near the water! Discovery Channel's annual Shark Week returns for its 27th year beginning Sunday, with a dozen new specials and the return of its late-night talk show "Shark After Dark." All this week, we're previewing some of this year's best new programs. But to whet your appetite, here are 51 cool facts about sharks.

Sharks don't have bones. Instead, they have tough, flexible cartilage similar to the cartilage humans have in their ears and nose. Cartilage allows sharks to be more flexible so they can get closer to their prey.

Most sharks are a shade of gray or brown. But sharks can be colorful, too. The goblin shark is bright pink, and mako sharks are a sleek metallic blue.

Thin-skinned politicians could learn a thing or two from sharks. Whale sharks have skin that's up to 3-1/2 inches thick – the thickest skin on any animal on land or sea.

The whale shark may live up to 150 years, making it one of the longest-living creatures on Earth.

Whale sharks are anything but aggressive. They ignore or swim away from humans when they see them.

Whale sharks are the world's biggest fish – and they have big families, too. One whale shark can give birth to 300 live shark pups in one litter.

The smallest sharks are the dwarf lantern shark and pygmy shark, which are only 6 inches long.

Some sharks are notorious enough to have earned a nickname. Tiger sharks are often referred to as "garbage guts" because they'll eat just about anything – license plates, car parts and even tires have been found in their stomachs. Bull sharks are sometimes called shovelnoses because they hit their prey with their snouts.

Sharks have keen senses. They can hear low-frequency sounds from more than a mile away, and can smell things that are more than half a mile away. And they've got electroperception, a sense that alerts them to the electrical impulses that all living things give off. These senses work together to give them amazing hunting and survival skills.

Talk about the silent treatment! Sharks don't have vocal chords, and no evidence has ever been gathered of sharks making vocal sounds.

Swell sharks swallow water and swell in size to intimidate their predators.

The jaws of large sharks are about twice as powerful as the jaws of a lion and can generate up to 40,000 pounds per square inch of pressure in a single bite.

Shark meat has an unpopular image as food, so fish markets and chefs change the name of shark meat to rock salmon, rock eel, huss or flake.

Port Jackson sharks lay eggs that have a corkscrew shape.

Basking sharks suck in more than 10,000 quarts of plankton-filled water in one hour.

Sharks have 5 to 7 pairs of gills on the sides of their heads, which they use to extract oxygen from water.

Great white, mako and salmon sharks will drown if they stop moving because water won't pass over their gills.

Some sharks have strong cheek muscles and can store water in their mouths to force over their gills.

Shipwrecks are like a playground for sharks. Hulls sink to the ocean floor, where they eventually develop their own ecosystems, attracting all manner of marine life, including sharks.

Very few of the more than 350 species of shark – a small minority – are known to attack humans.

Sharks don't actually chew their prey, but tear it up into chunks and swallow.

Sharks' eyes are on the sides of their heads, so they have an amazingly wide sightline spanning nearly 360 degrees.

Sharks have highly tuned inner ears that help them hear their prey from a distance of up to two city blocks away.

The cookiecutter shark is a master of camouflage. This shark's underside glows, with the exception of a small strip on its neck that looks like a much smaller fish.

Predators mistake this strip for a snack, and the cookiecutter takes a bite of their flesh before swimming away.

A shark's tooth-shaped scales are designed for dynamic movement but have also been mimicked in biotechnological research for their ability to repel barnacles and algal growth.

Sharks can sense injured fish that make infrasonic sound vibrations in the water and quickly become an easy dinner.

Some shark species moms can be pregnant for up to two years.

Sharks living in frigid waters can heat their eyes using a special organ next to a muscle in their eye socket to keep hunting their prey in extreme temperatures.

Sharks never run out of teeth. They have new ones on a "conveyor belt" at the ready to move up and replace any that become lost during feeding. Some sharks can produce over 30,000 teeth in their lifetime.

Sharks have existed almost unchanged for 400 million years – long before the dinosaurs – and yet are at risk from human activities such as fishing.

50-foot megalodon sharks swam the oceans for more than 50 million years, but became extinct about 35 million years ago. These sharks inspired

Salmon sharks are the world's fastest sharks and can swim up to 55 miles per hour.

Great white sharks eat more than 20 times what a human eats in a year.

The bluntnose sixgill shark can dive as deep as 7,550 feet, or the length of more than five Empire State Buildings.

The largest shark family, scyliorhinidae, is comprised of about 90 catsharks, many of which are commonly called dogfish.

Baby sharks are called pups, male sharks are called bulls and female sharks are just called females.

Shark pups are born or hatch fully nourished. While they can swim right away, they don't need to hunt for food for the first few weeks of their lives.

What happens to sharks when they get old? If they evade other predators, they die from heart or liver problems, kidney failure, or other diseases – just like us.

Shark life expectancy varies dramatically. Blue sharks only live for about 16 years, while Greenland sharks can live up to 200 years ago. That means there could be sharks alive now that were born when James Madison was in the White House.

People think of tropical waters when they think of sharks, but some sharks can survive in freezing waters, like Greenland sharks, slow-moving sea sharks that typically swim about a mile below the ocean's surface. They are the northernmost of all sharks.

Talk about your social network! While some sharks are loners, hammerheads gather in schools. No one is sure why, but it may be to help protect themselves from larger predators, or to help males find mates.

Hammerhead sharks have been around for millions of years – long enough for different species to develop different-shaped heads.

Do sharks ever sleep? Many species need to keep moving to keep water moving over their gills, but some sharks can find places where the ocean currents are strong enough to keep water flushing over their gills, allowing for short naps.

Many male sharks let females know they are interested in mating by biting them. That's why female sharks develop tough skin – sometimes three times as thick as the males in their species.

Blue sharks are notorious for over-eating, but that doesn't mean they are fatties. Some food may remain in their bodies undigested for days or even weeks until it's needed for energy. That allows them to keep swimming even during periods when food isn't readily available.

Bull sharks are one of the few varieties that can live in either salt or fresh water. That's why they've been spotted in the Mississippi River as far north as Illinois, and why they were found in Lake Pontchartrain in the aftermath of Hurricane Katrina.

Bull sharks are anything but docile. They're territorial and will attack when threatened – even animals that are larger than them.