No-Prey-Remains

Type: Fish

Diet: Carnivore

Size: 15 ft (4.6 m) to more than 20 ft (6 m)

Weight: 5,000 lbs (2,268 kg) or more

Group name: School or shoal

Did you know? Great whites can detect one drop of blood in 25 gallons (100 liters) of water and can sense even tiny amounts of blood in the water up to 3 miles (5 kilometers) away.

Protection status: Endangered

Size relative to a bus:

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).

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 coloration 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 silhouette 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.

Size

A typical adult great white shark measures 4–4.8 metres (13–16 ft) and has a mass of 680–1,100 kilograms (1,500–2,400 lb), females generally being larger than males. The great white shark's maximum size is about 6 m (20 ft), with a maximum weight of about 2,000 kg (4,400 lb). The maximum size of the great white shark 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 caught: an 11 m (36 ft) great white captured in Southern Australian waters near Port Fairy in the 1870s, and an 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 and often deemed credible.
 

Some researchers questioned the reliability of both measurements, noting they were much larger than any other accurately-reported great white shark. The New Brunswick shark may have been a misidentified 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 ft) in length and suggested that a mistake had been made in the original record, in 1870, of the shark's length.^[10]

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 other experts have argued this individual might have been a few feet shorter. The unverified weight reported for the shark from Cuba was 3,270 kilograms (7,200 lb). There have since been claims of larger great white sharks, but, as Ellis and McCosker note, verification is often lacking and these extraordinarily large great white sharks have, upon examination, all proved under the 6.1–6.4 m (20–21 ft) limit. For example, a much-publicized female great white said to be 7.13 m (23.4 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 7.13 m (23.4 ft) 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 5.6 m range (18.3 ft) range and in no way approaches the 7 m (23 ft) reported by Abela." (as in original)^[11]

According to the Canadian Shark Research Centre, the largest accurately measured great white shark was a female caught in August 1988 at Prince Edward Island off the Canadian (North Atlantic) coast and measured 6.1 m (20 ft). The shark was caught by David McKendrick, a local resident from Alberton, West Prince. McKendrick and a man by the name of David Livingstone have the first and second biggest teeth from this shark.^[11]

The question of maximum weight is complicated by the unresolved question of whether or not to account for the weight of a shark's recent meals when weighing the shark itself. With a single bite, a great white can take in up to 14 kg (31 lb) of flesh, and can gorge on several hundred kilograms or pounds 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 recent scientifically measured examples weigh in at about 2 metric tons (2.2 short tons). Other large, predatory sharks may grow to comparable lengths as the Great White, including the Tiger shark^[12], the Greenland Shark^[13] and the Pacific sleeper shark^[14]. 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 shark 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 white sharks caught by anglers have since been verified, but were later disallowed from formal recognition by IGFA monitors for rules violations.
 

Adaptations
 

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, which if close enough the shark can detect even that faint electrical pulse.^[15] 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 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 (25 °F) ^[16] 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.

Diet

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 also 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.^[17] 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.^[18]

The great white is regarded as an apex predator with its only real threats from humans. Although their diets overlap greatly, great whites do not seem to directly compete with orcas and there are few reports of encounters between them. The average orca is larger and faster which is probably why the sharks do not bother to compete.^{[citation needed]} In one recorded incident a female orca killed a subadult great white and her calf ate the shark's liver.^[19] Pods of dolphins can kill a great white shark through mobbing behaviour in which the dolphins ram the shark.^{[citation needed]} Great whites are also sometimes cannibalized by larger specimens.^{[clarification needed]}

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. Near the now-famous Seal Island, in South Africa's False Bay; studies have shown that the shark attacks most often occur 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 is 55% in the first 2 hours, it falls to 40% in late morning and after that the sharks stop hunting.^[20]

The hunting technique of the white shark varies with the species it hunts. When hunting Cape fur seals off Seal Island, South Africa, the shark will ambush it from below at high speeds and hit the seal at mid-body. They go so fast that they actually breach out of the water. The peak burst speed of these sharks is largely accepted in the scientific community to be above at least 40 kilometers per hour (25 mi/h), however further precision is still regarded as speculation and obviously depends on the individual shark.^[21] They have also been observed chasing their prey after a missed attack. The prey is usually attacked at the surface.^[22]

When hunting Northern elephant seals off California, the shark immobilizes the prey with a large bite to the hindquarters (which is the main source of the seal's mobility) and waits 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 a great white 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 in mid-body before being dragged and eaten.^[23]

When hunting dolphins and porpoises, white sharks attack them from above, behind or below to avoid being detected by their echolocation. Among the species targeted are dusky dolphins, harbour porpoises, Risso's dolphins and Dall's porpoises.^[24]

A new study from the University of New South Wales in Sydney, Australia, is using CT scans of a shark's skull and complex computer models to measure the maximum bite force of the great white. The study will reveal what forces and behaviours the carnivore's skull is adapted to handle and will help resolve competing theories about its feeding behaviour.^[25]

Behavior

The behavior and social structure of the white shark 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, white sharks tend to space out and resolve conflicts with rituals and displays.^[20] 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 their personal space is intruded upon, white sharks give the intruder a warning bite. Another possibility is that white sharks softly 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 a behaviour learned from interaction with humans (it is theorized that the shark may also be able to smell better this way, because 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 clear waters off of Isla Guadalupe, Mexico).

Reproduction

There is still a great deal that is unknown about great white shark behaviour, such as their mating habits. Birth has never been observed, but several pregnant females have been examined. Great white sharks are ovoviviparous, the eggs developing in the female's uterus, hatching there and continuing to develop until they are born. The great white has an 11 month gestation period, with the shark pup's powerful jaws beginning to develop in the 1st month. The unborn sharks are thought to participate in a phenomenon known as intrauterine-cannibalism in which the strongest pups consume their weaker womb-mates. This behavior is known to occur in several other species of shark as well. The delivery is thought to take place in the period between spring and summer.

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.

Great White Sharks take around 15 years to reach sexual maturity. The lifespan of the great white has not been definitively established, although many sources estimate that great whites live 30 to over 100 years. It would not be unreasonable to expect such a slow maturing animal to live longer than other, faster maturing varieties.^[26]

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.^[31] 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.^[32]

Shark attacks

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.^[27] While great white sharks 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 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. Further research shows that they can tell in one bite whether or not the object is worth the energy for attacking. Humans, for the most part, are far too bony for their liking. They'd much prefer a fat, protein-rich seal.^[28]

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 dove 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 wounded 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.^[29]

Humans, in any case, are not appropriate prey for white sharks as 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 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."^[30] However, such comments should be taken in context; interaction between humans and canines 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.