Sharks are unique because they have flexible, light skeletons made from cartilage and teeth that grow back if they're lost. Fish float by filling their swim bladders with air. Sharks have to rely on a buoyant, or lighter than water, chemical in their livers, which make up 30% of their bodies. Since they can't float naturally, they start to sink if they stop swimming.
Right after the whale shark comes the world's second largest shark, the basking shark. The largest basking shark was caught in 1851 and was over 40 feet long. Basking sharks are filter feeders, just like whale sharks. They filter 2,000 tons of water per hour to draw out plankton and small fish.
Unlike most sharks, blue sharks live in groups. They swim in tropical oceans and deep water, giving birth to up to 100 shark pups at a time. They are lazy hunters and long-distance swimmers, sometimes traveling between New England and South America. The only danger they present to humans is their habit of traveling in large, scary-looking groups.
Bull sharks live in shallow waters all around the world. Unlike most other sharks, they can swim in fresh water and often make their way up rivers and streams. Because of this, bull sharks are responsible for most shark attacks on humans. They're naturally solitary and very aggressive, so don't get too close.
The great white shark is the largest sea predator, growing up to 21 feet and weighing 5,000 pounds. It doesn't have feeling in anything but its mouth, so the great white bites before it eats to see what an object is. Great white sharks have been caught biting buoys, piers, surfboards and yes, humans. It's more likely to bite, though, not kill, even though many people believe otherwise.
Scientists have been puzzling over the hammerhead for years. Why is its head shaped like a hammer, with its eyeballs and nostrils on the end? Sharks use an electric field to sweep the water for prey, this process is called electrolocation. It turns out that the hammerhead's unique head makes it ten times more sensitive to electric fields than other sharks.
The leopard shark is a bottom feeder, eating mollusks, crustaceans and small fish off of the ocean floor. It has a spotted pattern to blend in with rocks and sand, and a mouth on its belly. Unlike most sharks, this one has a very specific habitat. It lives in the Pacific Ocean from Oregon down to Baja California.
Tiger sharks are among the biggest sharks. They can grow to be 14 feet long and weigh 1400 pounds. They get their name from dark stripes on the side of their bodies which fade as the shark gets older. Tiger shark attacks are a big problem, especially in Hawaii. The tiger shark is one of the most dangerous sharks in the world.
The whale shark gets its shape from a shark, but its way of eating from a whale. It feeds on plankton by flushing water through its fine filters. The whale shark is unlike its shark cousins because it is a very inefficient swimmer, topping out at speeds of 3 miles per hour.