Shark Facts from HowStuffWorks

How Sharks Work
Sharks aren't just hunters -- they're survivors. They sit atop the apex of the ocean’s food chain and are among the most fearsome creatures on Earth. However, they're also one of the most sophisticated and enduring species known to man, with fossils dating back 300 million years before the dinosaur age. Take a look at the anatomy, senses and daily life of the shark. And get up close to their scariest attributes, their teeth and jaws -- if you dare.

Why do people collect shark teeth?
Shark teeth can be found on just about any beach, but some spots are hotter than others for hunting. Venice, Fla., the self-proclaimed " shark tooth capital of the world” brings out collectors in droves. Sharks lived in the area for millions of years, and beach erosion has helped surface some long-buried incisors over the years. And because sharks shed and regenerate teeth constantly -- one might last a week while others suffice for just 24 hours -- the area is always ripe with washed-up chompers. But what exactly drives people to unearth these buried sea collectibles? Read on to find out…

Could shark cartilage help cure cancer?
Take a quick stroll down your local pharmacy’s vitamin aisle and you'll see various powdered and capsuled supplements that contain shark cartilage. It’s a $25 million industry that began with a simple theory: Sharks didn’t get cancer, therefore, shark cartilage may help humans combat the disease as well. So is it true? Do people who take these supplements live longer? And what does the FDA think about it? Get the facts.

How are shark pups born?
If you think explaining reproduction to a child is difficult, try explaining it to a shark. There isn’t just one way for a shark to give birth. There are three: live birth, hatching from an egg or -- oddly enough -- an egg and live birth combination. Even stranger than that, in some shark species, pups have to survive gestation without being eaten by their developing siblings, and that’s no easy feat. It’s called intrauterine cannibalism, and it happens when embryos eat other fertilized or unfertilized eggs in the womb.

How do sharks see, smell and hear?
When you go swimming or scuba diving in the ocean, your senses are limited. You can't keep your eyes open underwater for a long time. The only thing you can smell might be the salt of the sea. And while you may be able to hear splashing or nearby boats, these sounds are likely muffled. Sharks, on the other hand, are at a clear advantage in the deep. They have advanced sensory systems that enable them to locate their prey, avoid their predators and find a mate. This is part of why they're so scary: Sharks can find us, but we can't find them.

How many sharks are killed recreationally each year -- and why?
In the few million years that sharks have been around, they've survived everything Mother Nature has thrown at them. So you’d think they'd be around for another couple hundred million years. But this may not be the case. Research indicates that about 100 million sharks are killed each year by humans -- roughly 11,000 sharks every hour around the clock. And these numbers may be on the low side, since the estimate is based only on those catches that are reported. So how many sharks are caught without being reported?

What is electroreception -- and how do sharks use it?
HowStuffWorks author Cristen Conger puts it succinctly: Sharks are literally wired for hunting. These finned predators of the high seas are equipped with a special sense called electroreception, an asset that allows them to hone in on prey with deadly accuracy. Yes, other members of the elasmobranch fish family, including rays and skates, share this trait, but sharks' electroreception abilities are the most finely tuned. Read more about how sensitivity to electrical currents helps sharks feed.

Why are goblin sharks called that?
Beady eyes, an enormously flat snout and retractable jaws make for a bizarre face you might find in a Picasso painting. A goblin shark's elongated nose creates a strange facial proportion while three rows of nearly 25 crooked, needlelike teeth line its gums. To top it all off, a goblin shark’s jaws also sit strangely on its face due to a double set of ligaments that let them extend and retract them for feeding purposes. Yes, goblin sharks are definitely the ugly ducklings of the shark family. So, is their appearance tied to their name? Find out.

Why is a cookiecutter shark called that?
Judging by its brown, slender profile, a cookiecutter looks almost docile -- especially compared to a great white or tiger shark. Often referred to as “cigar sharks,” they grow to be about only 20 inches in length. And while they may have weak fins and a rather puny lbody, this shark’s smile belies its cute name. With 30 to 37 teeth on its top palate and 25 to 31 along its bottom jaw, it’s obvious why cookiecutters are still a scary sight. So where did the name come from? And why is their bite so distinctive? Find out in this article.

Will a shark drown if it stops moving?
Think of all the things you might have on your schedule on a given day. Hit the gym, go to work, do laundry, manage a household, make meals – you know the drill. Now imagine you have to do all these things, all day long … while exercising. Perhaps that is what it’s like for a shark. It has to hunt for prey, meet mates and remain hyper-aware of its predators (other fish and humans alike). But does it have to continually swim just to stay alive, like many of us assume? If so, how do they sleep? Find out in this article from HowStuffWorks.com.

Can flapping fish really attract sharks?
Scenario: You love animals. Sad-eyed shelter puppies begging to be taken home and treated like part of the family. Skinny stray cats. Sweet fuzzy rabbits – even while eating your backyard plants – are just plain lovable. And this compassion doesn’t end at the shoreline. You feel the same sense of responsibility to help hurt fish and other aquatic life. Say, there's a fish flapping around in the surf right now. Should you run to its rescue? Is there a reason to think twice? Perhaps so. Read why.

Does light attract sharks?
Most sharks have keen peeping perception. Of course, there are always exceptions to the rule. Bull sharks are nearly blind and use their sense of smell to find prey. But due to many millions of rod cells found in sharks' eyes -- the same cells humans have – some sharks see as well as 10 times better in dim environs than we do. Sharks' eyes have an added feature that our eyes don't: a membrane in the back of a shark's eye increases their sensitivity to light so they can see better in murky water. The bad part? A shark has a good chance of seeing you before you see it.

Exactly how strong is a shark's bite?
Imagine peering into a great white shark’s mouth: intimidating jaws filled with rows of jagged, flesh-ripping teeth. It may seem clear that these chompers are quite capable of some major destruction. But exactly how strong is a shark's bite? That’s what HowStuffWorks writer Josh Clark wanted to know. “As it turns out, the image of a shark biting through anything in its path is largely unfounded. Shark bites aren't quite as strong as we might imagine,” he writes. How could this be? I mean, we’ve all seen Jaws, right?

Can wearing magnets really repel a shark?
During experiments in the Bahamas, scientists with the company SharkDefense stumbled upon something interesting: when they dropped a magnet in water near a shark, it would swim away. Why? The simple explanation is that the charged metals and salt water interacted to produce a weak, but effective, magnetic field. When the sharks approached, this field disrupted their “sixth sense” of electroperception (for more on this topic, read the HowStuffWorks article What is electroperception and how do sharks use it?). So, given the scientists’ results, can swimmers toss a few magnets in their swimsuits and wade out safely into shark-infested waters? Read on to find out.