GREAT WHITE SHARK

Habitat & Distribution

The great white shark is found mostly in temperate seas throughout the world's oceans. It makes infrequent visits to cold waters and has been recorded off Alaska and Canada. Great whites can be found along the temperate coastlines of the world, as the map below shows.

The white shark lives mainly in the upper part of the water column, near the shore. However, it ranges from the surf line to well offshore and from the surface to depths of over 775ft (250m). This shark commonly patrols small coastal islands inhabited by pinnipeds, (seals, sea lions and walruses) offshore reefs, banks and rocky headlands where there is deep-water close to shore. The white shark usually cruises either just off the bottom or near the surface.

Great White Shark

Order - Lamniforme Family - Lamnidae

Genus - Carcharodon

Species - Carcharias

World Distribution Map for the White Shark

Movement

Although information about the white shark's movements is limited, some information has been gathered through tag-and-release programs in the United States, South Africa and Australia. These studies reveal that the white shark is capable of making movements on local, regional and intercontinental scales.

Generally, it is the larger individuals that undertake long journeys across the great oceans. The great white is also capable of short, high-speed pursuits and even launching itself clear from the water (breaching). They are propelled through the water by their powerful tails, and they use their fins for balance. Sharks swim constantly, otherwise they will sink as they don't have a buoyant swim bladder like other fish.

Distinctive Features

Unlike the true fishes, sharks don’t have internal bone, but instead have a cartilaginous skeleton.

About halfway between Hawaii and the Baja coast is an area researchers dubbed the “café,” a gathering spot for the usually solitary ani-mals. It is speculated the purpose is to forage and mate. Peak time at the café is April to July, when many males hang out there and females drop by. Most of these sharks spend winters nearer to the coasts of Hawaii or North America.

The great white is one of the largest species of shark. The snout is short and conical. The eye is circular and solid black. The five gill slits are long, and all in front of the pectoral fin. The tail fin support area (caudal peduncle) has a wide lateral keel that strengthens the fin’s movement. The caudal fin is crescentic (both upper and lower lobes are about the same size). The upper part of the body, roughly on a line through the eye to the pelvic fin, is dark to light grey. Below this, the body is white. This coloration helps to camouflage the shark when approaching prey.

Size

Males reach maturity at between 11 and 13 feet and females at 15 to 16 feet. Most great white sharks encountered are 12-16 feet long. The largest reliable measurements for white sharks are: length 21 feet, weight 4,140 pounds. On a per-length basis, great whites from California waters seem more massive than those from other regions.

Arrangement of Teeth

The teeth of the great white are large, arrowhead-shaped and serrated. They have about 3,000 teeth at any one time. The teeth are in rows, which rotate when needed. As teeth are lost, broken or worn down, teeth rotate in to replace them.

Top tooth Bottom tooth

Male Female

Social Behavior Of Great White Sharks

White sharks are intelligent and have one of the largest brains for their body size of any animal - more similar to mammals than other fish. Their sense organs are outstanding. Great whites primarily use their sense of smell and their ability to sense the electrical fields of other animals.

Great whites are usually solitary animals but are occasionally seen in pairs. Scientists are beginning to understand more about the behavioral interactions between great whites. Sharks definitely interact with each other and communicate using body language. For instance stiff, arched bodies and gaping mouths (underwater) seem to be threat displays warning off other sharks. Some of the great white's swimming habits, such as a carefully timed turn away between two sharks on approaching courses, is interpreted as maintenance of individual space. Paral-lel swimming with two sharks heading in the same direction also seems to be a means for the shark to preserve its space from others.

When white sharks feed on the same prey, it doesn't make sense for one to bite and wound the other as this may reduce either shark's future ability to catch prey. For this reason white sharks use displays in order to discourage other sharks. White sharks have been observed with their caudal fin out of the water slapping the surface, usually in the direction of a second shark. This "tail slap" is the most common avoidance display shown by white sharks.

Sometimes a white shark will position itself between prey and another shark, preventing the second shark from feeding. White sharks have also been known to propel their body out of the water and land flat against the surface, causing a large splash. This behavior is called a breach and may represent a similar message as the tail slap. Breaching might also help remove external parasites, attract a mate or may be the result of a vertical charge approach toward its prey.

Reproduction

White sharks are ovoviviparous. Fertilization of the eggs occurs in the female; later the eggs hatch inside her and she gives birth to live young. Embryos are nourished through ingestion of unfertilized eggs, as there is no placenta. Their size at birth ranges from 47-59 inches in length. The new-born shark is not cared for by the mother, and swims away from her immedi-ately after birth.

Scientists are uncertain of when the female becomes reproductive but their estimates range between 10-14 years. White sharks are likely to produce litters of 4 to 11 pups. Gestation time is unknown, but is thought to be quite long, possibly up to 14 months. Scientists don't know how many litters a female produces in her lifetime and aren't sure how long after the last litter a female becomes receptive again. As in other species of sharks, the male white shark most likely bites the female during mating. Predators

The white shark is an apex predator (on top of the food chain) and as such, has very few predators and a relatively small population. Killer whales and larger sharks pose the only natural threat to an adult white shark. Humans are the greatest threat. Despite being rare, the white shark's rate of capture by humans is alarmingly high. This is due partly to the increasing value of its jaws and teeth. Their fins are also used for shark fin soup. In the despicable practice of finning the fins are sliced off of the shark and then the living animal is left to die. When fully utilized, the flesh is eaten, the skin used for leather, the liver for oil and the carcass for fishmeal. As an apex predator, its population is not large. The National Marine Fisheries Service estimates there are 3,000 individuals (young of the year to adult) in the North East Pacific population.

Food & Feeding

The white shark is a macro predator that is active during the daytime. Its most important prey are marine mammals (including, seals, sea lions, elephant seals, dolphins) and fish (including other sharks and rays). Marine birds and sea otters are commonly found having suffered injuries from encounters with white sharks, but are rarely eaten by them.

The white shark has multiple attack strategies available. With large pinnipeds such as elephant seals, the attack is a fast upward vertical strike at the hindquarters of the prey. The shark then backs off to allow the prey to bleed out and avoid a struggle.

An attack on smaller marine mammals may involve an initial strike from below or from the surface. The prey may be dragged under and held there until it drowns. If the first bite tells the shark that the prey is low in fat, or not even an animal, the prey will be released. Their intelligence means they are able to adapt their hunting strategy depending on the prey. In shallow waters they often use stealthy ambush techniques to capture seals. Occasionally great whites swim with their ventral side up and perform an inverted approach. White sharks sometimes scavenge from fishermen's nets and long lines—often resulting in accidental injury to the shark.

The Elephant Seal and White Sharks

The behavior of elephant seals gives them some advantages against white sharks. Because most pinnipeds live in coastal waters, and most of their hunting is done at depths above 500 feet, that is where sharks hunt. Elephant seals are protected by the fact that most of their time at sea is spent farther from the coast than other pinnipeds. Elephant seals are solitary creatures at sea and spend most of their time below depths normally hunted by white sharks making encounters between the two less likely.

The results of experiments reveal that when white sharks have a choice between a square target and a seal-shaped target, they select the seal shape, as it is more common in their natural environment. When only a single bait was presented, it was regularly investigated. Some scientists believe diver and surfer silhouettes, when viewed from below, resemble those of pinnipeds and that this misidentification by the shark is the cause of most white shark attacks on humans. Researchers suggest that white sharks often strike unfamiliar objects to determine their potential as food. Grasping an unfamiliar object would be the shark's only reliable method of determining whether it is suitable as prey. Great white sharks prefer energy rich prey, such as marine mammals, rather than less fatty, low energy prey.