Great white shark

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Great white shark, photo by National Geographic
The great white shark, scientific name Carcharodon carcharias, is also known as the Great white, White pointer, White shark, or White death, is a large lamniform shark found in coastal surface waters in all major oceans. The great white shark is known for its size, with the largest individuals known to have approached or exceeded 6 meters (20 ft) in length, and 2,268 kilograms (5,000 lb) in weight. This shark reaches maturity at around 15 years of age and can have a life span of over 30 years.

The great white shark is arguably the world's largest known extant macropredatory fish and is one of the primary predators of marine mammals. It is also known to prey upon a variety of other marine animals including fish, pinnipeds, and seabirds. It is the only known surviving species of its genus, Carcharodon, and is ranked first in a list of number of recorded attacks on humans. The IUCN treats the great white shark as vulnerable.

Humans are not the preferred prey of the great white shark.

Contents

Etymology

Carolus Linnaeus gave the 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.[10] Left: Megalodon tooth with two great white shark teeth and a U.S. quarter for size comparison

Ancestry

The great white shark came into existence during the Mid-Miocene epoch. The earliest known fossils are about 16 million years old. However, the phylogeny of the great white is still in dispute. The original hypothesis for the great white's origins is that it shares a common ancestor with a prehistoric shark, C. megalodon. Similarities among the physical remains and the extreme size of both the great white and C. megalodon led many scientists to believe that these sharks were closely related, and the name Carcharodon megalodon was applied to the latter.[11] However, a new hypothesis proposes that C. megalodon and the great white are distant relatives (albeit sharing the family Lamnidae), and that the great white is more closely related to an ancient mako shark, Isurus hastalis, than to C. megalodon. In addition, the new hypothesis assigns C. megalodon to the Carcharocles genus, which also comprises other megatoothed sharks, and Otodus obliquus is 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 and 24 °C (54 and 75 °F), with greater concentrations in the United States (Atlantic Northeast and California), South Africa, Japan, Australia (especially New South Wales and South Australia), New Zealand, Chile, and the Mediterranean. One of the densest known populations is found around Dyer Island, South Africa where much shark research is conducted.

It is an epipelagic fish, observed mostly in the presence of rich game like fur seals, sea lions, cetaceans, other sharks, and large bony fish species. In the open ocean it has been recorded at depths as great as 1,220 m (4,000 ft). These findings challenge the traditional notion about the great white as being a coastal species.

According to a recent study, California great whites have 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 (1,000 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 mating.[14]

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; 11,000 nmi) in under 9 months.

Anatomy and appearance

The great white shark has a robust large conical snout. The upper and lower lobes on the tail fin are approximately the same size (like some mackerel sharks).

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.

Size

Males reach maturity at 3.5–4.0 metres (11–13 ft) and females at 4.5–5.0 m (15–16 ft). Adults on average are 4–5.2 m (13–17.1 ft) long and have a mass of 680–1,100 kilograms (1,500–2,400 lb). Females are generally larger than males. It is widely accepted that the great white shark can reach 6.1 m (20 ft) in length and 1,900 kg (4,200 lb) in weight. The maximum size is subject to debate because some reports are rough estimations or speculations performed under questionable circumstances.

A number of very large great white shark specimens have been recorded. For 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. 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. Randall 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".

According to J. E. Randall, the largest white shark reliably measured was a 6.0 m (19.7 ft) individual reported from Ledge Point, Western Australia, in 1987. Another great white specimen of similar size has been verified by the Canadian Shark Research Center: A female caught by David McKendrick of Alberton, Prince Edward Island, in August 1988 in the Gulf of St. Lawrence off PEI. This female great white was 6.1 m (20 ft) long.[3] However, a larger great white shark specimen was verified by T. C. Tricas and J. E. McCosker in 1984. This specimen was 6.4 m (21 ft) long and had a body mass of about 3,324 kg (7,330 lb).

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 it is 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 stomach) at temperatures up to 14°C (25°F)[26] above that of 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. Bite force

Its 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 behavior 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). The white sharks are generally very curious animals, display intelligence and may also turn to socializing if the situation demands it. At Seal Island, white sharks have been observed arriving and departing in stable "clans" of two to six individuals on a yearly basis. Whether clan members are related is unknown but they get along peacefully enough. In fact, the social structure of a clan is probably most aptly compared to that of a wolf pack in that each member has a clearly established rank and each clan has an alpha leader. When members of different clans meet, they establish social rank nonviolently through any of a fascinating variety of interactions. Diet

Great white sharks are carnivorous and prey upon fish (e.g. tuna, rays, other sharks), cetaceans (i.e., dolphins, porpoises, whales), pinnipeds (e.g. seals, fur seals, and sea lions), sea turtles, sea otters, and seabirds. Great whites have also been known to eat objects that they are unable to digest. Upon approaching a length of nearly 4 metres (13 ft), great white sharks begin to target predominately marine mammals for food. These sharks prefer prey with a high content 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 from his boat in the South Farallons. The sharks attacked all three baits but rejected the sheep carcass.

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 brown 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, Risso's dolphins, bottlenose dolphins, Humpback dolphins, harbour porpoises, and Dall's porpoises. Close encounters between dolphins and predatory sharks often result in evasive responses by the dolphins. However, in rare cases, a group of dolphins may chase a single predatory shark away in an act of defense. White shark predation on some species of whales have also been observed. White sharks often attack and prey upon pygmy sperm whales, Kogia breviceps, in the Mediterranean Sea. In addition, white sharks also attack and prey upon beaked whales.

Even though the great whites are known to generally avoid conflicts with each other, the phenomenon of cannibalism is not alien to this species. Large individuals may aggressively interact intraspecifically with small individuals. A 3 m (9.8 ft) long great white shark was nearly bitten into two by a reportedly 6 m (20 ft) long great white shark in Stradbroke Island, near Brisbane in Australia.

Natural threats

Although the great white is typically regarded as an apex predator in the wild, it is in rare cases preyed upon by larger Orcas (also known as a Killer whales). Interspecific competition between the great white shark and the orca is probable in regions where dietary preferences of both species may overlap.

An incident was documented on October 4, 1997, in the Farallon Islands off California. An estimated 4.7–5.3-metre (15–17 ft) female orca immobilized an estimated 3–4-metre (9.8–13 ft) great white shark. The orca held the shark upside down to induce the tonic immobility and kept the shark still for fifteen minutes, causing it to suffocate and then proceeded to eat the dead shark's liver.

Another similar attack apparently occurred there in 2000, but its outcome is not clear. 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.

Breaching behavior

A breach is the result of a high speed approach to the surface with the resulting momentum taking the shark partially or completely clear of the water. This is a hunting technique employed by great white sharks whilst hunting seals. This behavior most often takes place on cape fur seals at Seal Island in False Bay, South Africa, and was first documented by photographer Chris Fallows. Here, in the region of 600 natural predatory events are recorded annually between April and September each year. The seals swim on the surface and the great white sharks launch their predatory attack from the deeper water below. They can reach speeds of up to 40 miles per hour and can at times launch themselves more than 10 feet in the air. Data recorded shows that the sharks are successful in just under 50% of all these natural predatory events. In 2011, a 3-metre long shark jumped onto a 7-person research vessel off Seal Island. The crew were undertaking a population study using sardines as bait, and the incident was judged to be an accident.

Relationship with humans

While great white sharks have killed 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.

The great white shark is one of only four kind of sharks that have been involved in a significant number of fatal unprovoked attacks on humans

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 the 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 generally rescued by their buddy. 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 the shark's digestion is too slow to cope with a human's 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 bite rather than from critical organ loss or from whole consumption. Since the year 2000 there have been a total of 66 unprovoked great white shark attacks, with only 14 of these attacks being fatal.

A shark conservationist, Jimmy Hall, reported and documented his personal encounter with a very large great white shark, nicknamed Schatzi, in December, 2005, in waters off Hawaii. This encounter received worldwide attention as it remained entirely peaceful. J. Hall was first cautious but later on swam with this shark without cage protection and touched it repeatedly while filming it simultaneously.

Dressed for Dinner

David Blaine shows how humans can interact with Great white sharks in his video Dressed For Dinner:

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