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Great white shark

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

                iGreat white shark

                             Conservation status

   Vulnerable (VU)
            Scientific classification

   Kingdom:  Animalia
   Phylum:   Chordata
   Class:    Chondrichthyes
   Subclass: Elasmobranchii
   Order:    Lamniformes
   Family:   Lamnidae
   Genus:    Carcharodon
             Smith, 1838
   Species:  C. carcharias

                                Binomial name

   Carcharodon carcharias
   (Linnaeus, 1758)
   Range (in blue)
   Range (in blue)

   The great white shark (Carcharodon carcharias), also known as white
   pointer, white shark, or white death, is an exceptionally large
   lamniform shark found in coastal surface waters in all major oceans.
   Reaching lengths of about 6 metres (20 ft) and weighing almost 2,000
   kilograms (4,400 lb), the great white shark is the world's largest
   known predatory fish. It is the only known surviving species of its
   genus, Carcharodon.

Distribution and habitat

   Great white sharks live in almost all coastal and offshore waters which
   have a water temperature of between 12 and 24°  C (54° to 75°  F), with
   greater concentrations off the southern coasts of Australia, off South
   Africa, California, Mexico's Isla Guadalupe and to a degree in the
   Central Mediterranean and Adriatic Seas. The densest known population
   is found around Dyer Island, South Africa where up to 31 different
   white sharks have been documented by Michael Scholl of the White Shark
   Trust in a single day. It can be also found in tropical waters like
   those of the Caribbean and has been recorded off Mauritius. It is a
   pelagic fish, but recorded or observed mostly in coastal waters in the
   presence of rich game like fur seals, sealions, cetaceans, other sharks
   and large bony fish species. It is considered an open-ocean dweller and
   is recorded from the surface down to depths of 1,280 metres (4,200 ft),
   but is most often found close to the surface.

   In a recent study white sharks from California were shown to migrate to
   an area between Baja California and Hawaii, where they spend at least
   100 days of the year before they migrate back to Baja. On the journey
   out, they swim slowly and dive to up to 900 metres (3,000 ft). After
   they arrive, they change behaviour and do short dives to about 300 m
   (1,000 ft) for up to 10 minutes. It is still unknown why they migrate
   and what they do there; it might be seasonal feeding or possibly a
   mating area.

   In a similar study a white shark from South Africa was tracked swimming
   to the northwestern coast of Australia and back to the same location in
   South Africa, a journey of 20,000  kilometres in under 9 months.

Anatomy and appearance

   The great white shark has a robust large conical-shaped snout. It has
   almost the same size upper and lower lobes on the tail fin (like most
   mackerel sharks, but unlike most other sharks). It is pale to dark grey
   and has a white stomach.

   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 tension-sensing nerve
   cells. This arrangement seems to give their teeth high tactile
   sensitivity. A great white's teeth are serrated and when the shark
   bites it will shake its head side to side and the teeth will act as a
   saw and tear off large chunks of flesh. Great whites often swallow
   their own broken off teeth along with chunks of their prey's flesh.
   These teeth frequently cause damage to the great white's digestive
   tract. However great whites often feed on stingrays and swallow the
   'sting' as well, the barbed sting often getting stuck in the shark's
   guts. There are anecdotal reports of the sting working its way out
   through the shark's side. Correspondingly, a tooth causes the shark no
   major harm.

Size

   The average length of a full grown great white is 4 to 4.8 metres (13.3
   to 15.8 ft), with a weight of 680 to 1,100 kilograms (1,500 to
   2,450 lbs), females generally being larger than males. But the question
   of the maximum size of a great white shark 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.
   A 3 to 4 m great white swimming in a shoal of mackerel scad off of Isla
   Guadalupe, Mexico in August 2006.
   Enlarge
   A 3 to 4 m great white swimming in a shoal of mackerel scad off of Isla
   Guadalupe, Mexico in August 2006.

   Today, most experts contend that the great white's "normal" maximum
   size is about 6 metres (20 ft), with a maximum weight of about
   1,900 kilograms (4,200 lb). Any claims much beyond these limits are
   generally regarded as doubtful, and are closely scrutinized.

   For some decades many ichthyological works, as well as the Guinness
   Book of World Records, listed two great whites as the largest
   individuals caught: an 11 metre (36 ft) great white captured in south
   Australian waters near Port Fairy in the 1870s, and an 11.3 metre (37.6
   ft) shark trapped in a herring wier in New Brunswick, Canada in the
   1930s. While this was the commonly accepted maximum size, reports of
   7.5 to 10 metre (25 to 33.3 ft) great whites were common and often
   deemed credible.

   Some researchers questioned the reliability of both measurements,
   noting they were much larger than any other accurately-reported great
   white. The New Brunswick shark may have been a wrongly-identified
   basking shark, as both sharks have similar body shapes. The question of
   the Port Fairy shark was settled in the 1970s, when J.E. Reynolds
   examined the shark's jaws and "found that the Port Fairy shark was of
   the order of 5 m (17 feet) in length and suggested that a mistake had
   been made in the original record, in 1870, of the shark's length.

   Ellis and McCosker write that "the largest White Sharks accurately
   measured range between 19 and 21 ft [about 5.8 to 6.4 m], and there are
   some questionable 23-footers [about 7 m] 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." (For more about legendary exaggerated shark measurements, see
   the submarine).

   The largest specimen Ellis and McCosker endorse as reliably measured
   was 6.4 metres (21.3 ft) long, caught in Cuban waters in 1945 (though
   confident in their opinion, Ellis and McCosker note, however, that
   other experts have argued this individual might have been a few feet
   shorter). Click here to see a photo of this Cuban shark.

   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 metres (over 23 ft) was fished in
   Malta in 1987 by Alfredo Cutajar. In their book, Ellis and McCosker
   agree this shark seemed to be larger than average, but they did not
   endorse the measurement. In the years since, 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 18.3 ft
   [5.5 m] range and NO WAY approaches the 23 ft [7 m] reported by Abela."
   (as in original)

   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 (North Atlantic) coast and measured
   6.1 metres (20.3 ft). The shark was caught by David McKendrick, a local
   resident from Alberton, West Prince.

   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 kilograms (30 lb) of flesh, and can gorge on several
   hundred kilograms or pounds of food.

   Ellis and McCosker write in regards to modern great whites that "it is
   likely that [great white] sharks can weigh as much as 2 tons", but also
   note that the largest recent scientifically measured examples weigh in
   at about 2  tonnes (1.75  short tons).

   The largest great white recognized by the International Game Fish
   Association (IGFA) is one landed by Alf Dean in south Australian waters
   in 1959, weighing 1,208 kilograms (2,664 lb). Several larger great
   whites caught by anglers have since been verified, but were later
   disallowed from formal recognition by IGFA monitors for rules
   violations.

Diet

   Great white sharks primarily eat fish, smaller sharks, turtles,
   dolphins, and pinnipeds such as seals and sea lions. Great Whites have
   also been known to eat garbage that can't be digested. In great white
   sharks above 3.41 metres (11 ft, 2 in) towards a diet consisting of a
   higher proportion of mammals has been observed. Sometimes, they swim so
   fast that they actually jump out of the water while chasing/attacking
   seals. They are apex predators; the only animals known to attack them
   as prey are other great whites, and orcas.

   Great whites are warm-bodied (certain parts of the body running at
   higher temperatures, while the heart and gills run at sea-temperature),
   keeping most of their body up to 14° C above the surrounding water,
   which would suggest a high metabolism. Despite that, the few estimates
   that have been made suggest they are economical with their calories and
   can go weeks between meals. Due to problems keeping great whites in
   captivity, no concrete figures for this exist.

Behaviour

   Great white sharks' reputation as ferocious predators is well-earned,
   yet they are not (as was once believed) indiscriminate "eating
   machines". They typically hunt using an "ambush" technique, taking
   their prey by surprise from below. Off Seal Island in South Africa
   studies have shown that the shark attacks most often in the morning,
   within 2 hours after sunrise. The reason for this is that it is hard to
   see a shark close to the bottom at this time. The success rate of
   attacks in average is 55% in the first 2 hours, it falls to 40% in late
   morning and after that the sharks stop hunting. Sometimes, they swim so
   fast that they actually jump out of the water while chasing/attacking
   seals. This is one of only a few sharks that can jump fully out of the
   water, the others are thresher shark, shortfin mako, longfin mako,
   spinner shark, basking shark, blacktip shark, salmon shark, porbeagle
   shark and the copper shark. This is the only shark known to regularly
   lift its head above the sea surface to gaze at other objects such as
   prey; this is known as " spy-hopping". This behaviour has also been
   seen in at least one group of blacktip reef sharks, but this might be a
   behaviour learned from interaction with humans (it is theorized that
   the shark may also be able to smell better this way, since smells
   travel through air faster than through water). They are very curious
   animals, and can display a high degree of intelligence and personality
   when conditions permit (such as in the crystal-clear waters of Isla
   Guadalupe, Mexico).

Capabilities

   Great whites, like all other sharks, have an extra sense given by the
   Ampullae of Lorenzini, which enables them to detect the electromagnetic
   field emitted by the movement of living animals. Every time a living
   creature moves it generates an electrical field and great whites are so
   sensitive they can detect half a billionth of a volt. This is
   equivalent to detecting a flashlight battery from 1,600 kilometres
   (1,000  miles) away. Thus a great white's sense of sight is useful, but
   the shark does not depend on it. A shark primarily uses its extra
   senses (i.e, electrosense and mechanosense) to locate prey from far
   off. Then, the shark uses smell and hearing to further verify that its
   target is food. At close range, the shark utilizes sight for the
   attack. The shark will often in ambush deliver a massive disabling bite
   and then back off to allow the prey to expire. This tactic allows the
   animal to avoid combat with dangerous prey, such as sea lions. It also
   has allowed occasional rescue of humans bitten by the animal, though it
   appears to attack humans mostly in error.

Reproduction

   There is still a great deal that is unknown about great white
   behaviour, 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 or 9 (with a maximum of perhaps 14) for a
   single delivery, are about 1.5 metres (5 ft) long when born. Their
   teeth are provided with small side cusps. They grow rapidly, reaching
   2 metres of length in the first year of life. Almost nothing, however,
   is known about how and where the great white mates. There is some
   evidence that points to the near-soporific effect resulting from a
   large feast (such as a whale carcass) possibly inducing mating.

   A white shark can reproduce when a male's length is around 3.8 metres
   (12 ft) and a female's length is around 4 to 4.8 metres (13.3 to 15.8
   ft). Their lifespan has not been definitively established, though many
   sources estimate 30 to 40 years. It would not be unreasonable to expect
   such a large marine animal to live longer however.

Relationship to humans

Shark attacks

   A large great white shark cruising offshore from the Farallon Islands.
   Enlarge
   A large great white shark cruising offshore from the Farallon Islands.

   More than any documented attack, Steven Spielberg's 1975 film Jaws
   provided the great white with the image of a "man eater" in the public
   mind. While great whites have been responsible for fatalities in
   humans, they typically do not target humans as prey: for example, in
   the Mediterranean Sea there were 31 confirmed attacks against humans in
   the last two centuries, only a small number 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, and might grab 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. 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.

   However some researchers have hypothesized that the reason the
   proportion of fatalities is low is not because sharks do not like human
   flesh, but because humans are often able to get out of the water after
   the shark's first bite. In the 1980s John McCosker noted that divers
   who dived solo and were attacked by great whites were generally at
   least partially consumed, while divers who followed the buddy system
   were normally pulled out of the water by their colleagues before the
   shark could finish its attack. Tricas and McCosker suggest that a
   standard attack modus operandi for great whites is to make an initial
   devastating attack on its prey, and then wait for the prey to weaken
   before going in to consume the ailing animal. A human's ability to get
   to land (or onto a boat) with the help of others is unusual for a great
   white's prey, and thus the attack is foiled.

   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 and Tyler B. write 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 ( POD) worn by the diver/surfer that creates an
   electric field which disturbs the shark's sensitive electro-receptive
   sense organs, the Ampullae of Lorenzini.

Great white sharks in captivity

   All attempts to keep a great white shark in captivity prior to August
   1981 lasted 11 days or less. However, that month a great white broke
   previous records by lasting 16 days in captivity at SeaWorld San Diego
   before being released into the wild.

   In 1984, shortly before opening day, the Monterey Bay Aquarium in
   Monterey, California housed its first great white, which died after 10
   days. 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. 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 Ventura, was kept in the aquarium's massive 1 million-gallon
   (3,800,000 L) Outer Bay exhibit for 198 days before her successful
   release back to the wild in March 2005. She was tracked for 30 days
   after her early morning release. On the evening of August 31, 2006 the
   aquarium introduced a second shark to the Outer Bay exhibit. The
   juvenile male, caught outside Santa Monica Bay on August 17 , had its
   first official meal in captivity (a large salmon steak) on September 8,
   2006 and as of that date, the shark was estimated to be 1.72 metres
   (5 ft 8 in) and to weigh approximately 47 kilograms (104 lb).

   Probably the most famous great white to be kept in captivity was a
   female named "Sandy", which in August 1980 became the first and only
   great white to be housed at the Steinhart Aquarium in San Francisco,
   California. She was returned to the wild because she would not eat
   anything given to her and constantly bumped against the walls.

Shark tourism and cage diving

   Viewing sharks from the safety of a cage gives tourists an adrenaline
   rush and has become a booming industry. Common practice is to chum the
   water to draw in sharks for the tourists to view. These practices have
   raised the fear that as a result of this form of tourism, sharks are
   becoming accustomed to people in their environment and beginning to
   associate human activity with food - a potentially dangerous situation.

   Tour companies respond that they are being made the scapegoats, as
   people try to find someone to blame for shark attacks on humans. Most
   point out that lightning tends to strike more often than sharks bite.
   Their position is that further research needs to be done before banning
   practices such as chumming which are said to alter sharks natural
   behaviour.

Conservation status

   It is unclear how much a concurrent 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 tagged great white named "Nicole" was recorded swimming from
   South Africa to Australia and back, a 22,000 kilometre round trip.
   Researchers believe it may have undertaken this journey to mate, and
   hope studies such as this will produce more effective conservation
   measures.

   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. The great 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.

Related species

   Dental features and the extreme size of both the great white and the
   megalodon, Carcharodon megalodon, lead some scientists to believe they
   were closely related, however there is much doubt about this hypothesis
   and other scientists would place the megalodon and white shark as
   distant relatives - sharing the family Lamnidae but no closer
   relationship. Megalodon is only known from its teeth, and may have
   reached sizes of 12 metres (40 ft) or more, considerably larger than
   even the largest white sharks. From time to time it is suggested that
   megalodon might still exist. Megalodon teeth have been found from as
   recently as 10,000 to 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.

   Other evidence suggests that the great white is more closely related to
   the mako shark than to the megalodon.
   Retrieved from " http://en.wikipedia.org/wiki/Great_white_shark"
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