Great White Sharks |
The Great White Shark (Carcharodon carcharias), also known as White Pointer, White Shark or Amaletz, is an exceptionally big lamniform shark found in coastal surface waters in all major oceans. Reaching lengths of about 6 meters (20 feet) and weighing over 2000 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. Distribution Capabilities 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 lifts its head above the sea surface to gaze at other objects such as prey. This is known as 'spy-hopping'. It is theorized that the shark may also be able to smell better this way, since smells travel through air faster than through water. Great White sharks primarily eat fish, smaller sharks, turtles, dolphins, and pinnipeds such as seals and sea lions. They are apex predators; the only animals known to attack them are other Great Whites, sperm whales and orcas. 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. Their teeth also rotate on their own axis (outward when the jaw is opened, inward when closed). The teeth are linked to pressure and tensor-sensing nerve cells. This arrangement seems to give their teeth high tactile sensitivity.
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. It should be noted that there is some evidence that points to the near-soporific effect as the result of a large kill (such as a large whale) possibly inducing mating. 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 has not been definitively established, though many sources estimate 30 - 40 years. It would not be unreasonable to expect such a large marine animal to live longer however. Captivity In 1984, the Monterey Bay Aquarium in Monterey, California housed its first Great White. [2] However, in July 2003, Monterey researchers captured a small female and kept it in a large, netted pen off Malibu for five days, where they had the rare success of getting the shark to feed in captivity before it was released. [3] It was not until September 2004 that the aquarium made history by becoming the first aquarium in the world to place a Great White on long-term exhibit. The young female, who was caught off the coast of Orange County, was kept in the aquarium's massive 1 million-gallon Outer Bay exhibit for 198 days before her successful release back to the wild in March 2005. [4] Probably the most famous Great White to be kept in captivity was "Sandy" and in August 1980 she became the first and only Great White to be housed at the Steinhart Aquarium in San Francisco, California. She was returned to the wild when she would not eat anything given to her and would constantly bump against the walls.
In 2005, a tagged Great White named Nicole was recorded swimming from South Africa to Australia and back, 22,000 kilometers round trip. Researchers believe it may have undertaken this journey to mate, and hope studies such as this will produce more effective conservation measures. [6] 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 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, and are closely scrutinized. For some decades, many standard ichthyology reference books listed an 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 J.E. Reynolds examined the Port Fairy shark's jaws and "found that the Port Fairy shark was of the order of 5 m (17 feet) in length".[7] 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 as reliably measured is a 6.4 m (21 ft) caught in Cuban waters in 1945. There have since been claims of larger Great Whites, but, as Ellis and McCosker note, verification is often lacking and these extraordinarily large Great Whites have, upon examination, all proved of average size. For example, a female said to be 7.13 meters (over 23 feet) was fished in Malta in 1987 by Alfredo Cutajar, but experts eventually found reason to doubt the claim, due in no small part to conflicting accounts offered by Cutajar and others. A BBC photo analyst concluded that even "allowing for error ... the shark is concluded to be in the 18 ft [5.5m] range and NO WAY approaches the 23 ft [7 m] reported by Abela." (as in original) [8] According to the Canadian Shark Research Centre, the largest accurately measured Great White shark was a female caught in August 1983 at Prince Edward Island off the Canadian coast (North Atlantic) and measured 6.1 m (20 ft). 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 [Great White] 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 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. Many attacks occur in waters with low visibility, or other situations in which the shark's senses are impaired. It has been speculated that the species typically does not like the taste of humans, or at least that the taste is unfamiliar. Humans, in any case, are not healthy 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 most recorded attacks, Great Whites have broken off contact after the first bite. Fatalities are usually caused by loss of blood from the initial limb injury rather than from critical organ loss or from whole consumption. 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." [9] 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.
Recent scientific documentation proposes that the Great White is not related to the Megalodon. New theories suggest that they originate from different species lines (see the Megalodon entry). However, as of now, it is most widely accepted that the Megalodon belongs in the Carcharodon family. Source - From Wikipedia, the free encyclopedia. |