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. Most fish have a less developed but similar ability in the horizontal line along their body.
To more successfully hunt fast moving and agile prey such as sea lions, the poikilothermic great white shark has developed adaptations that allow it 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 above the surrounding water, while the heart and gills remain at sea-temperature. When conserving energy (a great white shark can go weeks between meals), 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.
A typical adult great white shark measures 4 to 4.8 m (13 to 16 ft) with a typical weight of 680 to 1,100 kg (1,500 to 2,450 lb), females generally being larger than males. The maximum size of the 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 analysing various accounts of extreme size. Today, most experts contend that the great white shark's "normal" maximum size is about 6 m (20 ft), with a "normal" maximum weight of about 1,900 kg (4,189 lb).
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). Great white sharks 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 colouration makes it difficult for prey to spot the shark because it breaks up the shark's outline when seen from a lateral perspective. When viewed from above, the darker shade blends in with the sea and when seen from below casts a minimal silloutte against the sunlight.
Great white sharks, like many other sharks, have rows of teeth behind the main ones, allowing any that break off to be rapidly replaced. A great white shark'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 white sharks often swallow their own broken off teeth along with chunks of their prey's flesh.
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. One of the densest known populations is found around Dyer Island, South Africa where much research on the shark is conducted. 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, sea lions, 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 m (4,199 ft), but is most often found close to the surface.
In a recent study great 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 down to around 900 m (2,953 ft). After they arrive, they change behaviour and do short dives to about 300 m (984 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 great 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 km (12,428 mi) in under 9 months.
The white shark is an exceptionally large lamniform shark found in coastal surface waters in all major oceans. Reaching lengths of about 6 m (20 ft) and weighing up to 2,250 kg (5,000 lb), the great white shark is the world's largest known predatory fish. It is the only surviving species of its genus, Carcharodon.
The great white is classified as a mackerel (Lamnidae) shark. There are four other living species in this family, two mako and two Lamna sharks. Dental features and the extreme size of both the great white and the prehistoric Megalodon lead 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.[2] According to this theory, the extinct broad tooth mako, Isurus hastalis, is considered to be the true ancestor of the great white, while the megalodon has strong ties with the sharks belonging to Carcharocles genus. In this case, Otodus obliquus is considered to be the ancient representative of the extinct Carcharocles lineage; indeed, Carcharocles megalodon is a popular alternative classification of the megalodon.
Megalodon is only known from its teeth and from a few cartilage remains, and probably reached sizes of 15 m (49 ft) or more, considerably larger than even the largest great white sharks. From time to time it is suggested that megalodon might still exist. Megalodon teeth have supposedly been found from as recently as 10,000 to 13,000 years ago, but these results appear to be based on misinterpretation of the evidence.[3] However, while megalodon fossils are widespread and plentiful, no evidence has surfaced that the species is anything but extinct.
