The truth about great white sharks

It goes by several common names. The most widespread is "great white shark", but Australians call it the "white pointer" and scientists simply refer to the "white shark".

In fact, great white sharks are not white. The epithet is thought to have come about because these sharks are predominantly white in one circumstance: when they are lying dead, belly-up on the deck of a boat.

It would arguably be more appropriate to call this species the "black shark". They have a dark upper surface, which means their surface-dwelling prey struggle to spot them approaching from the murky depths.

Speaking of prey, they have been recorded dining out on a wide range of species, including whales, squid, turtles and occasionally penguins.

"If you make a list of everything that's been found in a white shark's stomach, you'd get a variety of things," says marine biologist George Burgess of the University of Florida in Gainesville. But what's clear is that their tastes change as they age.

"They are almost exclusively fish-eaters until they are 7, 8, 9 feet long," says Burgess. "As they get bigger and reach sexual maturity, they will begin to start eating mammal prey if they get the opportunity."

These older sharks prefer seals, sea lions and walruses. When they strike from below, at speed, white sharks can clear the surface by as much as 3m.

To locate their prey, white sharks use almost every trick in the book. "They have a series of senses that are overlapping and complementary," says Burgess.For starters they have surprisingly nifty hearing.

In a 1963 study, researchers hung a speaker over the edge of their boat off Miami to see if they could attract sharks with sound. Low-frequency pulses, rather like those produced by a distressed fish, resulted in a rash of shark sightings.

No great white sharks were spotted in this study, but it's reasonable to assume they have good hearing too.

As a great white gets closer to its prey, its legendary sense of smell begins to kick in. A study of the brains of different species of shark shows that the great white's olfactory bulb is especially large.

Their vision is not bad, either. "They see contrasts particularly well," says Burgess.

They also have two less familiar senses. Their lateral lines, which run along their sides, can detect changes in water pressure that reveal their prey's movements. Once they are really close to their target, they can pick up electromagnetic fields.

"All of those things come together making this a very, very efficient predator," says Burgess. But they rarely apply their hunting skills to humans.

(BBC)