Great white shark

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 which is similar to some mackerel sharks.

A great white displays countershading, by having a white underside and a grey dorsal area 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.

Distribution

Great white sharks live in almost all coastal and offshore waters which have water temperature between 12 and 24 °C , with greater concentrations in the United States , South Africa, Japan, Oceania, Chile, and the Mediterranean. One of the densest known populations is found around Dyer Island, South Africa, where almost all of the shark research is done.

The great white is an epipelagic fish, observed mostly in the presence of rich game, such as 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 1,200 m ....hieroglyph snipped... 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 the 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 . After they arrive, they change behavior and do short dives to about 300 m for up to ten minutes. Another white shark that was tagged off of the South African coast swam to the southern coast of Australia and back within the year. A similar study tracked a different great white shark from South Africa swimming to Australia's northwestern coast and back, a journey of 20,000 km in under nine months.
These observations argue against traditional theories that white sharks are coastal territorial predators, and open up the possibility of interaction between shark populations that were previously thought to have been discrete. The reasons for their migration and what they do at their destination is still unknown. Possibilities include seasonal feeding or mating.

Status

It is unclear how much of 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 global population numbers are available, but the great white shark is now considered vulnerable. Sharks taken during the long interval between birth and sexual maturity never reproduce, making population recovery and growth difficult.

The IUCN notes that very little is known about the actual status of the great white shark, but as it appears uncommon compared to other widely distributed species, it is considered vulnerable. It is included in Appendix II of CITES, meaning that international trade in the species requires a permit. As of March 2010, it has also been included in Annex I of the CMS Migratory Sharks MoU, which strives for increased international understanding and coordination for the protection of certain migratory sharks. A February 2010 study by Barbara Block of Stanford University estimated the world population of great white sharks to be lower than 3,500 individuals, making the species more vulnerable to extinction than the tiger, whose population is in the same range.

Fishermen target many sharks for their jaws, teeth, and fins, and as game fish in general. The great white shark, however, is rarely an object of commercial fishing, although its flesh is considered valuable. If casually captured , it is misleadingly sold as ''smooth-hound shark''.

Behavior

This shark's behavior and social structure is not well understood. In South Africa, white sharks have a dominance hierarchy depending on the 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 to another great white, they react with a warning bite. Another possibility is that white sharks bite to show their 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 . 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.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 often takes place on cape fur seals at Seal Island in False Bay, South Africa but due to the randomness of the location of a shark's breach, it was very hard to document. It was first photographed by Chris Fallows and Rob Lawrence who developed the technique of towing a slow moving seal decoy to trick the sharks to breach. Here, in the region of 600 natural predatory events are recorded annually from April to 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 kilometres per hour and can at times launch themselves more than 10 feet into the air. Data recorded shows that the sharks are successful in just under 50% of all these natural predatory events. In 2011, a 3 metres long shark jumped onto a seven-person research vessel off Seal Island in Mossel Bay. The crew were undertaking a population study using sardines as bait, and the incident was judged to be an accident.

Habitat

Great white sharks live in almost all coastal and offshore waters which have water temperature between 12 and 24 °C , with greater concentrations in the United States , South Africa, Japan, Oceania, Chile, and the Mediterranean. One of the densest known populations is found around Dyer Island, South Africa, where almost all of the shark research is done.

The great white is an epipelagic fish, observed mostly in the presence of rich game, such as 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 1,200 m ....hieroglyph snipped... 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 the 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 . After they arrive, they change behavior and do short dives to about 300 m for up to ten minutes. Another white shark that was tagged off of the South African coast swam to the southern coast of Australia and back within the year. A similar study tracked a different great white shark from South Africa swimming to Australia's northwestern coast and back, a journey of 20,000 km in under nine months.
These observations argue against traditional theories that white sharks are coastal territorial predators, and open up the possibility of interaction between shark populations that were previously thought to have been discrete. The reasons for their migration and what they do at their destination is still unknown. Possibilities include seasonal feeding or mating.This shark's behavior and social structure is not well understood. In South Africa, white sharks have a dominance hierarchy depending on the 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 to another great white, they react with a warning bite. Another possibility is that white sharks bite to show their 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 . 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.

Reproduction

Almost nothing is known about reproduction in great whites. Some evidence points to the near-soporific effect of a large feast possibly inducing mating. Great white sharks also reach sexual maturity at around 15 years of age. Maximum life span was originally believed to be more than 30 years, but in a study by the Woods Hole Oceanographic Institute, the true lifespan of the great white shark was revealed to be up to 70 years or more with examinations of growth ring count in vertebrae including ages of 73 years old in the oldest male and 40 years old in the oldest female in the study, making the species far more vulnerable to pressures such as overfishing and environmental change. .

Little is known about the great white shark's behavior in the way of mating habits. Birth has never been observed, but pregnant females have been examined. Great white sharks are ovoviviparous, which means 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 oophagy, in which they feed on ova produced by the mother. Delivery is in spring and summer. The Northern Pacific population of great whites is suspected to breed off of the Sea of Cortez , as evidenced by local fisherman who have said to have caught them and evidenced by teeth found at dump sites for discarded parts from their catches. If the Sea of Cortez is such a breeding ground, it is imperative that the area's laws be better enforced to ensure the survival of the breeding population.

Food

Great white sharks are carnivorous and prey upon fish , cetaceans , pinnipeds , 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 , 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.

The great white shark's reputation as a ferocious predator is well-earned, yet they are not indiscriminate "eating machines". They are ambush hunters, taking prey by surprise from below. Near 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 species of the prey. Off Seal Island, the sharks 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 . 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 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 taken from the surface and dragged 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.

Off The East Coast of North America, where white sharks are still poorly understood, individuals have been filmed and documented hunting grey seals. When hunting, atlantic great whites will hunt very close to shore, unlike their counterparts elsewhere which prefer deeper water for ambush and breach attacks. The sharks also utilize sandbars to set up ambushes, and will then chase the seals in a flat-out pursuit. This behavior was revealed to the public media during two episodes of Shark Week, the first being "Jaws Comes Home" and the second being "Return of Jaws".

White sharks also 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 other species of small cetacean has also been observed. In August 1989, a 1.8 metres juvenile male pygmy sperm whale, ''Kogia breviceps'', stranded in central California with a bite mark on its caudal peduncle from a great white shark. 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 long great white shark was nearly bitten into two by a reportedly 6 m long great white shark in Stradbroke Island, near Brisbane in Australia.

White sharks also scavenge on whale carcasses. In one such documented incident, white sharks were observed scavenging on a whale carcass alongside tiger sharks.

Predators

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 4 October 1997, in the Farallon Islands off California in the United States. An estimated 4.7–5.3-metre female orca immobilized an estimated 3–4-metre great white shark. The orca held the shark upside down to induce tonic immobility and kept the shark still for fifteen minutes, causing it to suffocate and then proceeded to eat the dead shark's liver. It is believed that the scent of the slain shark's carcass caused all the great whites in the region to flee, forfeiting an opportunity for a great seasonal feed. 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 a depth of 500 m and swum to Hawaii.

Evolution

The great white shark came into existence during the mid-Miocene epoch. The earliest known fossils of the great white shark 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, such as the ''C. megalodon''. Similarities among the physical remains and the extreme size of both the great white and ''C. megalodon'' led many scientists to believe these sharks were closely related, and the name ''Carcharodon megalodon'' was applied to the latter. However, a new hypothesis proposes that the ''C. megalodon'' and the great white are distant relatives . The great white is also more closely related to an ancient mako shark, ''Isurus hastalis'', than to the ''C. megalodon'', a theory that seems to be supported with the discovery of a complete set of jaws with 222 teeth and 45 vertebrae of the extinct transitional species Carcharodon hubbelli in 1988 and published on 14 November 2012. In addition, the new hypothesis assigns ''C. megalodon'' to the genus ''Carcharocles'', which also comprises the other megatoothed sharks; ''Otodus obliquus'' is the ancient representative of the extinct ''Carcharocles'' lineage.