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Smith, 1838
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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 (20 feet) and weighing near 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.
Diffusion
White sharks live in almost all the cold or temperate waters of the planet, with greater concentrations in the southern coasts of Australia, in South Africa, California and Central Mediterranean. It can be also found in hotter waters like those of the Caribbean or the Adriatic Sea. It is a pelagic fish which reaches the coasts only in the presence of rich game like tunnies, otaries or penguins.
Capabilities
Great Whites have a sixth sense given by the Ampullae of Lorenzini, which permits them to detect the electromagnetic field emitted by the movement of living animals. It has been recently discovered, anyway, that their main and most refined sense is their sense of sight. Individuals who lose, partially or totally, their sense of sight can scarcely survive.
White shark's reputation as ferocious predators is well-earned, yet they are not (as once was believed) indiscriminate "eating machines". They hunt using an "ambush" technique, taking their prey by surprise from the bottom. It is the one shark that uses its head to gaze from the sea surface.
Great White sharks primarily eat fish, smaller sharks, turtles, dolphins and pinnipeds such as seals and sea lions. They are apex preadators; the only animals known to attack them are other Great Whites, sperm whales, orcas, and humans.
Great Whites, like many other sharks, have rows of teeth behind the main ones, allowing any that break off to be rapidly replaced. 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.
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 embryos can feed off unfecundated eggs. The delivery takes place in the period transitioning Spring and Summer.
The young, which number 8-9 (with a maximum of perhaps 14) for a single delivery, are about 1.5 m (5 ft) long when born. Their teeth are provided with small side cusps. They grow rapidly, reaching 2 meters of length in the first year of life. Almost nothing, however, is known about how and where the Great White mates.
A White Shark can reproduce when a male's length is around 3.8 meters and a female's length is around 4.5 to 5 meters. Their lifespan is not known, but 14 to 15 years is a generally accepted estimate.
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 population 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 population can take a long time to rise.
In 2005, a Great White was followed swimming from South Africa to Australia. Researchers believe it may have undertook this journey to mate and hope studies such as this will produce more effective conservation measures.
A Great White shark named "Sandy" is the only recorded Great White shark being kept in a zoo. She was returned to the wild when she would not eat anything given to her and would constantly bump against the walls which injured her badly. If she remained, she would have died.
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. White shark, however, is rarely an object of commercial fishing, although its flesh is considered valuable. If casually captured (it happens for example in some tonnare in the Mediterranean), it is sold as Smooth-hound shark.
Size
While the average length of a Great White is 3 to 4 m (females generally being larger than males), the maximum size of Great White sharks has been subject to much debate, conjecture and misinformation. Richard Ellis and John E. McCosker, both academic shark experts, devote a full chapter in their book The Great White Shark (1991) to analysis of various accounts of extreme size.
For some decades, many standard ichthyology reference books listed a 11 m (36 feet) Great White captured in south Australian waters near Port Fairy in the 1870s as the largest individual. While this was the commonly accepted maximum size, reports of 7.5 to 10 m (25 to 30 ft) Great Whites were common and often deemed credible.
Some researchers questioned the reliability of the Port Fairy shark, noting it was much larger than any other accurately reported Great White. The question was settled in the 1970s, when examination of the shark's jaws revealed it was actually about 5 m (16 to 17 ft) long, and the error assumed likely a typographical error.
Ellis and McCosker write that "the largest White Sharks accurately measured range between 19 and 21 ft (about 6 m), and there are some questionable 7 m (23 feet) in the popular — but not the scientific — literature". Furthermore, they add that "these giants seem to disappear when a responsible observer approaches with a tape measure."
The largest specimen Ellis and McCosker endorse is a 6.4 m (21 ft) caught in Cuban waters in 1945, though other sources speaks of a size of even 7.9 m. A 7/7.8 m feminine was fished in Malta in 1987.
Today, most experts contend that the Great White's "normal" maximum size is about 6 m (20 ft), with a maximum weight of about 1900 kg (4200 lb). Any claims much beyond these limits are generally regarded as doubtful.
The question of maximum weight is complicated by an unresolved question: when weighing a Great White, does one account for the weight of the shark's recent meals? With a single bite, a Great White can take in up to 14 kg (30 lb) of flesh, and can gorge on several hundred pounds or kilograms of food.
Ellis and McCosker write that "it is likely that sharks can weigh as much as 2 tons", but also note that the largest verified examples weigh in at about 1.75 short tons (1.6 metric tons).
The largest Great White recognized by the International Game Fish Association is one landed by Alf Dean in south Australian waters in 1959, weighing 1208 kg (2664 lbs). Several larger Great Whites caught by anglers have since been verified, but were later disallowed from formal recognition by IGFA monitors for rules violations.
Attacks on Humans
While Great Whites have been responsible for occasional fatalities in humans, they typically do not target humans as prey: for example, in the Mediterranean Sea there were 31 confirmed attacks against man in the last two centuries, only a small part of them deadly. 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 other situations 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."
Many "shark repellents" have been tested, some using scent, others using protective clothing, but to date the most effective is an electronic beacon worn by the diver/surfer that creates an electric field which disturbs the shark's sensitive electro-receptive sense, the Ampullae of Lorenzini
Occurrence in fiction
The Great White achieved high notoriety with Steven Spielberg's blockbuster movie, Jaws, in 1975 (based on the best-selling novel by Peter Benchley). It also occurred in the sequels: Jaws 2, Jaws 3-D and Jaws: The Revenge.
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.
Related articles
External links
- MarineBio: Great White shark, Carcharodon carcharias
- Review of the Great White shark
- Envirofacts: Great White Shark
Source
- Richard Ellis and John E. McCosker, The Great White Shark, Stanford University Press, 1991, ISBN 0804725292