Ranging in size from just a few inches to more than 52 feet long, the 400+ species of sharks are as diverse as the oceanic ecosystem that is their home.
Sharks only have one type of cone photoreceptor, compared with our three cone photoreceptors, so they can only see in black and white.
Though we enjoy the benefit of seeing color, sharks have the advantage of a sixth sense. They are able to sense even the slightest pulses, like that of an electrical field, a muscle movement or a heartbeat. Tiny organs in their snouts enable them to detect these pulses.
Mercury, arsenic and lead are found in high volumes in shark’s tissue, mostly as a result of their diet—which means you probably wouldn’t want to include shark meat in yours. Their meat has higher levels of heavy metal concentrations than any other fish.
The Hammerhead’s cranium gives them an edge as predators—and it’s not that they look intimidating. Researchers in the Bahamas discovered that Hammerheads can feed on the illusive sting ray by knocking it to the sea floor and pinning it down while feeding on it. Most other sharks with their rounded noses aren’t able to trap sting rays.
When Researchers in California trained cameras on fishing lures they caught footage of thresher sharks whipping the bait with their tails repeatedly. None of the sharks on tape tried to bite the bait first, they all attacked with their tails at lightning fast speeds. Other researchers observed thresher sharks attacking sardines in the same way and said the whipping crippled the sardines and even split some in half, which made them easy to eat after the initial attack.
Bull sharks have been spotted in rivers around the globe and have even attacked people in Rivers in Iran, India and South Africa.
In most major shark species, female sharks usually outweigh males.
In a typical year, sharks kill an average of six people—humans, on the other hand, kill up to 273 million sharks by some estimates. Conservative assessments put the rate of dead sharks closer to 100 million a year and their deaths are usually caused by fishermen who harvest and sell their fins and meat.