Shark Week: 12 Fascinating Facts to Know

It’s the most wonderful time of the year! No, it’s not Christmas; it’s Discovery Channel’s Shark Week, which kicks off Sunday, July 5.

To celebrate, we talked to our friends at The Maritime Aquarium at Norwalk in Connecticut to get some interesting (and surprising) facts about these mysterious (and sometimes feared) creatures.

There are more than 400 species of sharks in a great variety of sizes and shapes. Sharks range in size from the whale shark (up to 40 feet) to the dwarf lantern shark (just seven inches). Half of all shark species never grow larger than six feet long. Only 10 of all known shark species regularly reach 13 feet or more.
Of the 400+ species of sharks, fewer than 40 are known to have ever attacked humans. Scientists believe that often sharks attack humans by accident, confusing them for their normal prey.
The gestation period for spiny dogfish sharks is two years! This slow process of reproduction is why it can take so long for some endangered populations of sharks to rebound. Most sharks have a gestation period between six and 22 months.
Most sharks do not sleep like we sleep. But they do have periods of rest, which generally means slow movement. Most sharks have to keep moving to sustain water flow over their gills. But some species, such as nurse sharks, can sit on the ocean bottom without swimming. They’re able to do this, because they can pump water into their mouths and over their gills to breathe.
Tiger sharks have been found with random objects in their stomachs, including tires, license plates and more, earning them the nickname "garbage cans of the sea."
Female sand tiger sharks have two uteruses and will develop eggs inseminated by multiple males. The sand tiger shark embryos will eat each other in utero — in other words, they attack and feed on each other before being born. Only two will actually be born — one from each uterus.
The blue shark, on the other hand, can give birth to as many as 134 shark pups in one litter.
Because there are so many kinds of sharks, there are different kinds of shark mouths — each adapted to its feeding strategy. Whale sharks filter feed, so they have little teeth that are pretty much useless as far as biting or chewing goes. Smooth dogfish sharks have molar-like teeth more suited for crushing and grinding. Great whites, of course, have big triangular teeth with serrated edges for slicing through flesh. Most sharks have multiple rows of sharp teeth. When one tooth falls out, the one behind it moves forward to take its place — this is true for all sharks, but it happens more frequently for sharks that chomp down on food. A shark can have up to 30,000 teeth in a lifetime.
Shark skin is an evolutionary adaption that — instead of scales — actually consists of teeth-like structures called dermal denticles embedded in the skin. They lie flat to be hydrodynamic in the water as the shark moves. But rub a shark backward, from tail to head, and it will feel rough, like sandpaper, because you’ll be rubbing "against the grain."
Sharks have special ways to sense what’s going on around them. Some have excellent color vision (even in dim light) and an advanced sense of smell. Also, like all fish, they have something called a lateral line running down their bodies, which is sort of like a sense of touch that allows them to feel or detect impulses of movement in the water. And sharks have one more special sense that other fish don’t have: a specialized ability to detect the very faint electrical fields that living organisms emit. These sensory organs are called the ampullae of Lorenzini, and they can be seen as little dots on a shark’s head. So by detecting a flounder’s weak electrical field, a shark can find one buried in the seafloor at night. Pretty impressive!
Sharks actually have "friends" in the sea. The pilot fish is known to hang around sharks hoping to get some of the leftovers from the shark’s next meal, and the remora is a sort of hitchhiker. It has a suction cup on its head where it attaches to the bottom of a shark, grabs leftovers from any meals and returns the favor by eating parasites off the shark.
Some species of sharks, including the cookiecutter shark and the dwarf lantern shark, have organs (called photophores) that produce light. Their luminescence attracts curious prey.