Great white shark
The great white shark (Carcharodon carcharias), also known as great white, white pointer, white shark, or white death, is a large lamniform shark found in coastal surface waters in all major oceans. Reaching lengths of more than 6.50 metres (21 ft) and weighing up to 2,240 kilograms (4,938 lb), reaching sexual maturity at around 15 years of age and having a lifespan of 30 to over 100 years. The great white shark is arguably the world's largest known predatory fish, eating dolphins, porpoises, whale carcasses and pinnipeds such as seals, fur seals and sea lions. It is the only surviving species of its genus, Carcharodon.
The best selling novel Jaws and the subsequent film by Steven Spielberg provided the great white shark with the image of a "man eater" in the public mind even though humans are not appropriate prey for white sharks.
C.I.T.E.S. has listed the great white shark as an endangered species.
Carolus Linnaeus gave great white shark its first scientific name, Squalus carcharias in 1758. Sir Andrew Smith gave it the generic name Carcharodon in 1833, and in 1873 the generic name was identified with Linnaeus' specific name and the current scientific name Carcharodon carcharias was finalised. Carcharodon comes from the Greek words karcharos, which means sharp or jagged, and odous, which means tooth..
Dental features and the extreme size of both the great white and the prehistoric Megalodon led many scientists to believe they were closely related, and the name Carcharodon megalodon was applied to the latter. At present there is considerable doubt about this hypothesis, as many scientists would place the megalodon and white shark as distant relatives - sharing the family Lamnidae but no closer relationship. Latest research suggests that the great white shark is more closely related to the mako shark than to the megalodon. According to this theory, Isurus hastalis is the ancestor, while the megalodon has strong ties with Carcharocles genus. Otodus obliquus is thus the ancient representative of the extinct Carcharocles lineage.
Distribution and habitat
Great white sharks live in almost all coastal and offshore waters which have water temperature between 12 °C (54 °F) and 24 °C (75 °F), but they have been found in waters down to 12 °C (285 K) with greater concentrations off the southern coasts of Australia, South Africa, California, Mexico's Isla Guadalupe and to a degree in the Central Mediterranean (particularly the Adriatic Sea) and New Zealand, where they are a protected species. One of the densest known populations is found around Dyer Island, South Africa where much shark research is conducted. It can also be found in tropical waters like those of the Caribbean, and has been recorded off Mauritius, Madagascar, Kenya, the Seychelles and even the colder September waters of Massachusetts.
It is an epipelagic fish, observed mostly in inland tributaries in the presence of rich game like fur seals, sea lions, cetaceans, other sharks and large bony fish species. It is an open-ocean dweller and lives between the surface and 1,280 m (4,200 ft). It is most often found close to the surface.
According to a recent study, California great whites migrated to an area between Baja California and Hawaii known as White Shark Café, to spend at least 100 days before migrating back to Baja. On the journey out, they swim slowly and dive down to around 900 m (3,000 ft). After they arrive, they change behavior and do short dives to about 300 m (980 ft) for up to 10 minutes. Another white shark tagged off the South African coast swam to the southern coast of Australia and back within the year. This refuted traditional theories that white sharks are coastal territorial predators and opens up the possibility of interaction between shark populations that were previously thought to be discrete. Why they migrate and what they do at their destination is still unknown. Possibilities include seasonal feeding or possibly mating.
A similar study tracked a great white shark from South Africa swimming to Australia's northwestern coast and back, a journey of 20,000 km (12,000 mi) in under 9 months.
Anatomy and appearance
Great whites display countershading, having a white underside and a grey dorsal area (sometimes in a brown or blue shade) that gives an overall "mottled" appearance. The coloration makes it difficult for prey to spot the shark because it breaks up the shark's outline when seen from the side. From above, the darker shade blends with the sea and from below it exposes a minimal silhouette against the sunlight.
Great white sharks, like many other sharks, have rows of serrated teeth behind the main ones, ready to replace any that break off. When the shark bites it shakes its head side to side helping the teeth saw off large chunks of flesh.
A typical adult measures 4–5.2 metres (13–17 ft) and has a mass of 680–1,100 kilograms (1,500–2,400 lb). Females are generally larger than males. The great white shark's maximum size is about 6 m (20 ft), and its maximum weight of about 2,000 kg (4,400 lb).
The maximum size has been hotly debated. Richard Ellis and John E. McCosker, both academic shark experts, devote a full chapter in their book, Great White Shark (1991), to analyzing various accounts of extreme size.
For several decades, many ichthyological works, as well as the Guinness Book of World Records, listed two great white sharks as the largest individuals: a 10.9 m (36 ft) great white captured in Southern Australian waters near Port Fairy in the 1870s, and a 11.3 m (37 ft) shark trapped in a herring weir in New Brunswick, Canada in the 1930s. While this was the commonly accepted maximum size, reports of 7.5–10-metre (25–33 ft) great white sharks were common.
Some researchers question these measurements' reliability, noting they were much larger than any other accurately-reported sighting. The New Brunswick shark may have been a misidentified basking shark, as the two 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 ft) in length and suggested that a mistake had been made in the original record, in 1870, of the shark's length".
The largest specimen Ellis and McCosker endorse as reliably measured was 6.4 m (21 ft) long, caught in Cuban waters in 1945; though confident in their opinion, Ellis and McCosker note that other experts argue this individual might have been a few feet shorter. The unverified weight reported for the Cuban shark was 3,270 kilograms (7,200 lb). There have since been claims of larger great white sharks, but all proved under the 6.1–6.4 metres (20–21 ft) record. For example, a much-publicized female great white said to be 7.13 m (23.4 ft) was caught 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 7.13 m (23.4 ft) measurement. Experts now discount the claim, due 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 5.6 m range (18.3 ft) range and in no way approaches the 7 m (23 ft) reported by Abela." (as in original)
According to the Canadian Shark Research Center, the largest accurately measured great white shark was a female caught by David McKendrick of Alberton, West Prince, in August 1988 at Prince Edward Island. It measured 6.1 m (20 ft).
The question of maximum weight is complicated by the unresolved question of whether or not to include the shark's stomach contents when weighing the shark. With a single bite, a great white can take in up to 14 kg (31 lb) of flesh, and can consume several hundred kilograms of food.
Ellis and McCosker write in regards to modern great white sharks that "it is likely that [Great White] sharks can weigh as much as 2 tons", but also note that the largest scientifically-measured examples weigh in at about 2 metric tons (2.2 short tons). Other large, predatory sharks may grow to comparable lengths, including the Tiger shark, the Greenland Shark and the Pacific sleeper shark. However, the great white is the most massive predatory shark to exceed 6 metres (20 ft) and is the only one known to weigh more than 2 metric 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 kg (2,660 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.
Great white sharks, 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. Even heart beats emit a very faint electrical pulse. If close enough the shark can detect even that faint electrical pulse. Most fish have a less-developed but similar sense using their body's lateral line.
To more successfully hunt fast and agile prey such as sea lions, the great white has adapted to maintain a body temperature warmer than the surrounding water. One of these adaptations is a "rete mirabile" (Latin for "wonderful net"). This close web-like structure of veins and arteries, located along each lateral side of the shark, conserves heat by warming the cooler arterial blood with the venous blood that has been warmed by the working muscles. This keeps certain parts of the body (particularly the brain) at temperatures up to 14 °C (25 °F) above the surrounding water, while the heart and gills remain at sea-temperature. When conserving energy the core body temperature can drop to match the surroundings. A great white shark's success in raising its core temperature is an example of gigantothermy. Therefore, the great white shark can be considered an endothermic poikilotherm, because its body temperature is not constant but is internally regulated.
Ecology and behavior
This shark's behavior and social structure is not well understood. In South Africa, white sharks have a dominance hierarchy depending on size, sex and squatter's rights: Females dominate males, larger sharks dominate smaller sharks, and residents dominate newcomers. When hunting, great whites tend to separate and resolve conflicts with rituals and displays. White sharks rarely resort to combat although some individuals have been found with bite marks that match those of other white sharks. This suggests that when another shark approaches too closely, great whites react with a warning bite. Another possibility is that white sharks bite to show dominance.
The great white shark is one of only a few sharks 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 learned from interaction with humans (it is theorized that the shark may also be able to smell better this way, because smell travels through air faster than through water). They are very curious animals, and display intelligence and individuality when conditions permit (such as in the clear waters off of Isla Guadalupe, Mexico).
Great white sharks are carnivorous, and primarily eat fish (including rays, tuna, and smaller sharks), dolphins, porpoises, whale carcasses and pinnipeds such as seals, fur seals and sea lions and sometimes sea turtles. Sea otters and penguins are attacked at times although rarely, if ever, eaten. Great whites have been known to eat objects that they are unable to digest. In great white sharks above 3.41 metres (11 ft) a diet consisting of a higher proportion of mammals has been observed. These sharks prefer prey with high contents of energy-rich fat. Shark expert Peter Klimley used a rod-and-reel rig and trolled carcasses of a seal, a pig, and a sheep to his boat in the South Farallons. The sharks attacked all three baits but rejected the sheep carcass.
Although the great white is typically regarded as an apex predator whose only real predators are humans, they are occasionally preyed upon by the larger orca. While their diets greatly overlap, great whites do not seem to directly compete with orcas and there are few reports of encounters between them; the sharks may avoid areas with orcas. In one recorded incident in the Farallon Islands off California, a female orca killed a subadult great white and ate its liver. Another similar attack apparently occurred there in 2000. After both attacks, the local population of about 100 great whites vanished. Following the 2000 incident, a great white with a satellite tag was found to have immediately submerged to depth of 500 m and swum to Hawaii. Prior to the evolution of orcas, great whites may have similarly avoided the much larger shark C. megalodon. Great whites are also sometimes cannibalized by larger individuals.
Great white sharks' reputation as ferocious predators is well-earned, yet they are not (as was once believed) indiscriminate "eating machines". They are ambush hunters, taking prey by surprise from below. Near the now-famous Seal Island, in South Africa's False Bay, shark attacks most often occur in the morning, within 2 hours after sunrise, when visibility is poor. Their success rate is 55% in the first 2 hours, falling to 40% in late morning, after which hunting stops.
Hunting techniques vary by prey species. Off Seal Island the shark ambush cape fur seals from below at high speeds, hitting the seal mid-body. They go so fast that they can completely leave the water. The peak burst speed of these sharks is largely accepted in the scientific community to be above 40 kilometres per hour (25 mph). However further precision is still speculative. They have also been observed chasing prey after a missed attack. Prey is usually attacked at the surface.
Off California, sharks immobilize northern elephant seals with a large bite to the hindquarters (which is the main source of the seal's mobility) and wait for the seal to bleed to death. This technique is especially used on adult male elephant seals which can be as large or larger than the hunter and are potentially dangerous adversaries. Prey is normally attacked sub-surface. Harbour seals are simply grabbed from the surface and pulled down until they stop struggling. They are then eaten near the bottom. California sea lions are ambushed from below and struck mid-body before being dragged and eaten.
White sharks attack dolphins and porpoises from above, behind or below to avoid being detected by their echolocation. Targeted species include dusky dolphins, harbour porpoises, Risso's dolphins, bottlenose dolphins, and Dall's porpoises.
A 2007 study from the University of New South Wales in Sydney, Australia, used CT scans of a shark's skull and computer models to measure maximum bite force. The study reveals the forces and behaviors its skull is adapted to handle and resolves competing theories about its feeding behaviour.
Little is known about great white shark behavior, such as mating habits. Birth has never been observed, but pregnant females have been examined. Great white sharks are ovoviviparous (eggs develop and hatch in the uterus, and continue to develop until birth. The great white has an 11 month gestation period. The shark pup's powerful jaws begin to develop in the first month. The unborn sharks participate in intrauterine-cannibalism: stronger pups consume their weaker womb-mates. Delivery is in spring and summer.
Almost nothing is known about mating behavior. Some evidence points to the near-soporific effect of a large feast (such as a whale carcass) possibly inducing mating.
Great white sharks reach sexual maturity at around 15 years of age. Such a slow maturing animal may live longer than other, faster maturing species, and may live 30 to over 100 years.
Relationship with humans
More than any documented attack, Peter Benchley's best selling novel Jaws and the subsequent 1975 film adaptation directed by Steven Spielberg provided the great white shark with the image of a "man eater" in the public mind. While great white sharks have killed a few humans, they typically do not target them: for example, in the Mediterranean Sea there have been 31 confirmed attacks against humans in the last two centuries, most non-fatal. Many incidents seem to be "test-bites". Great white sharks also test-bite buoys, flotsam, and other unfamiliar objects, and might grab a human or a surfboard to identify it.
Other incidents seem to be cases of mistaken identity, in which a shark ambushes a bather or surfer from below, believing the silhouette is from a seal. Many attacks occur in waters with low visibility, or other situations which impair the shark's senses. The species appears to not like the taste of humans, or at least finds it taste unfamiliar. Further research shows that they can tell in one bite whether or not the object is worth attacking. Humans, for the most part, are too bony for their liking. They much prefer a fat, protein-rich seal.
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 escape after the first bite. In the 1980s John McCosker noted that divers who dove solo and were attacked by great whites were generally at least partially consumed, while divers who followed the buddy system were rescued by their colleagues. Tricas and McCosker suggest that a standard pattern for great whites is to make an initial devastating attack, and then wait for the prey to weaken before consuming the wounded animal. Humans' ability to move out of reach with the help of others, thus foiling the attack, is unusual for a great white's prey.
Humans, in any case, are not appropriate prey because shark's digestion is too slow to cope with the human high ratio of bone to muscle and fat. Accordingly, in most recorded attacks, great whites broke off contact after the first bite. Fatalities are usually caused by blood loss from the initial limb injury rather than from critical organ loss or from whole consumption.
Biologist Douglas Long writes that the great white shark's "role as a menace is exaggerated; more people are killed in the U.S. each year by dogs than have been killed by great white sharks in the last 100 years." However, such comments should be taken in context; human/canine interaction takes place far more regularly and in greater numbers than it does between humans and sharks.
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.
Attacks on boats
Great white sharks infrequently attack and sometimes even sink boats. Only 5 of the 108 authenticated unprovoked shark attacks reported from the Pacific Coast during the Twentieth Century involved kayakers. In a few cases they have attacked boats up to 10 metres (33 ft) in length. They have bumped or knocked people overboard, usually 'attacking' the boat from the stern. In one case in 1936, a large shark leapt completely into the South African fishing boat Lucky Jim, knocking a crewman into the sea. Tricas and McCosker's underwater observations suggest that sharks are attracted to boats due to the electrical fields they generate.
Great white sharks in captivity
Prior to August 1981, no great white shark in captivity lived longer than 11 days. In August 1981, a shark survived for 16 days at SeaWorld San Diego before being released. The idea of containing a live great white at SeaWorld Orlando was used in the 1983 film Jaws 3-D.
In 1984, shortly before its opening day, the Monterey Bay Aquarium in Monterey, California housed its first great white shark, which died after 10 days. In July 2003, Monterey researchers captured a small female and kept it in a large netted pen near Malibu for five days. They had the rare success of getting the shark to feed in captivity before its release. Not until September 2004 was the aquarium able to place a great white on long-term exhibit. A young female, who was caught off the coast of Ventura, was kept in the aquarium's massive 3,800,000-litre (1,000,000 US gal) Outer Bay exhibit for 198 days before she was released in March 2005. She was tracked for 30 days after release. On the evening of August 31, 2006 the aquarium introduced a juvenile male caught outside Santa Monica Bay His first meal as a captive was a large salmon steak on September 8, 2006 and as of that date, he was estimated to be 1.72 metres (68 in) and to weigh approximately 47 kilograms (100 lb). He was released on January 16, 2007 after 137 days in captivity.
In addition, Monterey Bay Aquarium housed a third great white, a juvenile male, for 162 days between August 27, 2007 through February 5, 2008. On arrival, he was 1.4 metres (4 ft 7 in) long and weighed 30.6 kilograms (67 lb). He grew to 1.8 metres (5 ft 11 in) and 64 kilograms (140 lb) at release. A juvenile female came to the Outer Bay Exhibit on August 27, 2008. While she swam well, the shark fed only one time during her stay and was tagged and released on September 7. Another juvenile female was captured near Malibu on August 12, 2009, introduced to the Outer Bay exhibit on August 26, and successfully released to the wild on November 4, 2009. 
Probably the most famous captive was a 2.4 metres (7.9 ft) female named "Sandy", which in August 1980 became the only great white to be housed at the California Academy of Sciences' Steinhart Aquarium in San Francisco, California. She was released because she would not eat and constantly bumped against the walls.
Their infamous reputation gives sharks great appeal for tourists. While it is safe to dive near sharks of most species, diving with great whites requires great care. One common approach is for divers to stay within a steel cage.
Cage diving is most common off the coasts of Australia, South Africa, and Guadalupe Island off the coast of Baja California, which great whites frequent. Cage diving has become a booming industry. A common practice is to chum the water with pieces of fish to attract sharks. These practices may make sharks more accustomed to people in their environment and to associate human activity with food—a potentially dangerous situation. By drawing bait on a wire towards the cage, tour operators lure the shark to the cage, possibly striking it, exacerbating this problem. Other operators draw the bait away from the cage, causing the shark to swim past the divers.
Companies object to being blamed for shark attacks, pointing out that lightning tends to strike humans more often than sharks bite humans. Their position is that further research needs to be done before banning practices such as chumming which may alter natural behaviour.
One compromise is to only use chum in areas in which whites actively patrol anyway, well away from human leisure areas. Also, responsible dive operators do not feed sharks; only sharks that are willing to scavenge follow the chum trail, and if they find no food at the end then the shark soon swims off and does not associate chum with a meal. It has been suggested that government licensing strategies may help enforce these suggested advisories.
The shark tourist industry has some financial leverage in conserving this animal. A single set of great white jaws can fetch a one-time price of up to £20,000. However, that is a fraction of the tourism value of a live shark, a more sustainable economic activity. For example, the dive industry in Gaansbai, South Africa, consists of six boat operators with each boat guiding 30 people each day. With fees between £50 to £150 per person, a single live shark that visits each boat can create anywhere between £9,000 to £27,000 of revenue daily.
It is unclear how much a concurrent increase in fishing for great white sharks has caused the decline of great white shark populations from the 1970s to the present. No accurate population numbers are available, but the great white shark is now considered endangered. Sharks taken during the long interval between birth and sexual maturity never reproduce, preventing population recovery.
The Convention on International Trade in Endangered Species (C.I.T.E.S.) has put the great white shark on its 'Appendix II' list of endangered species. Fishermen target many sharks 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.
From April 2007 great white sharks were fully protected within 370 kilometres (230 mi) of New Zealand and additionally from fishing by New Zealand-flagged boats outside this range. The maximum penalty is a $250,000 fine and up to six months in prison.
- ^ http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=83173&is_real_user=1
- ^ Fergusson, I., Compagno, L.; Marks, M. (2000). "Carcharodon carcharias in IUCN 2009". IUCN Red List of Threatened Species, Vers. 2009.1. International Union for Conservation of Nature and Natural Resources. View current version