Great White Shark
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| Great White Shark Conservation status: Vulnerable | ||||||||||||||||
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| Missing image Large_white_shark.jpg Great White Shark | ||||||||||||||||
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| Carcharodon carcharias (Linnaeus, 1758) |
The Great White Shark (Carcharodon carcharias), also known as White Pointer, White Shark or Amaletz, is an exceptionally large lamniform shark found in coastal surface waters in all major oceans. Reaching lengths of about 6 meters (about 21 feet) and weights of about 1,800 kilograms (4,000 pounds), the Great White is the world's largest predatory fish. They are the only known surviving species of their genus, Carcharodon.
Great Whites have excellent eyesight and can see in colour, and have highly-developed behaviors which are only now being researched. Their reputation as ferocious predators is well-earned, yet they are not (as once was believed) indiscriminate "eating machines". Great White sharks primarily eat fishes and pinnipeds such as seals and sea lions. Great Whites are apex predators; the only animals known to attack them are other Great Whites, sperm whales, humans, and orcas.
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Breeding, Behavior and Lifespan
There is still a great deal that is unknown about Great White behavior, such as mating habits. Birth has never been observed, but several pregnant females have been examined. Great Whites are ovoviviparous, the eggs developing in the female's uterus, hatching there and continuing to develop until they are born, at which point they are perfectly capable predators. The young are about 1.5 m (5 ft) long when born. Almost nothing, however, is known about how and where the Great White mates.
Their lifespan is not known, but 25 to 30 years is a generally accepted estimate.
Attacks on Humans
While Great Whites have been responsible for many fatalities in humans, they typically do not target humans as prey. Many incidents seem to be caused by the animals "test-biting" out of curiosity. Great white sharks are known to perform test-biting with buoys, flotsam, and other unfamiliar objects as well, grabbing a human or a surfboard with their mouth (their only tactile organ) in order to determine what kind of object it might be.
Other incidents seem to be cases of mistaken identity, in which a shark ambushes a bather or surfer, usually from below, believing the silhouette it sees on the surface is a seal.
Humans, in any case, aren't good for Great White sharks to eat, because the sharks' digestion is too slow to cope with the human body's high ratio of bone to muscle and fat. Accordingly, in nearly all recorded attacks, Great Whites have broken off contact after the first bite. Fatalities are caused by loss of blood from the initial injury. Most attacks also occur in waters with low visibility, or in other cases in which the shark's senses are impaired.
Biologist Douglas Long writes that the Great White's "role as a menace is exaggerated; more people are killed in the U.S. each year by dogs than have been killed by white sharks in the last 100 years."[1] (http://www.ucmp.berkeley.edu/vertebrates/Doug/shark.html)
Many "shark repellents" have been tested, some using smell, others using protective clothing, but to date the most effective is an electronic beacon worn by the diver/surfer that emits a high frequency signal disturbing to the shark's electromagnetic sensors.
Great Whites, like many other sharks, have rows of teeth behind the main ones, allowing any that break off to be replaced rapidly. Their teeth are unattached to the jaw and are retractable, like a cat's claws, moving into place when the jaw is opened. This arrangement also seems to give their teeth high tactile sensitivity.
Conservation status
It is unclear how much the film Jaws, and a consummate increase in fishing for Great Whites, had to do with the decline of Great White populations from the 1970s to the present. No accurate numbers on population are available, but populations have clearly declined to a point at which the Great White is now considered endangered. Their reproduction is slow, with sexual maturity occurring at about nine years of age, such that populations can take a long time to rise.
The Convention on International Trade in Endangered Species (Cites) has put the great white shark on its 'Appendix II' list of endangered species. The shark is targeted by fishermen for its jaws, teeth, and fins, and as a game fish.
Related species
These sharks have an extinct relative, the Megalodon (Carcharodon megalodon), which could possibly have reached sizes of 18 m (59 ft) or more, and is currently known only from its teeth. Megalodon is thought to have been similar to the White Shark, but substantially larger. From time to time it is suggested that Megalodon might still exist. Megalodon teeth have been found from as recently as 10,000–12,000 years ago, though some have questioned the reliability of these estimates. However, while Megalodon fossils are widespread and plentiful, no evidence has surfaced that the species is anything but extinct.