Great White Shark
The Great White shark is the largest known predatory fish in the sea. It is a solitary predator that is on average about 4.6 meters, but can reach lengths of over 6 meters long and weigh over 2,000 kg, females generally being larger than males. The white shark is a robust, torpedo-shaped shark with a conical-shaped snout. The upper and lower lobes of the caudal fin are about even in size, and its serrated triangular teeth are virtually symmetrical. Their teeth are unattached to the jaw and are retractable, like a cat's claws, moving into place when the jaw is opened. The upper teeth are triangular and sharply serrated, and are used for cutting large pieces of flesh from prey. Bottom teeth are narrower and not serrated, and are used to hold prey. Great whites, like many other sharks, have rows of teeth behind the main ones, allowing any that break off to be rapidly replaced. Despite its name the white shark is only white on its underside; the top of the shark is grey to black or blue.
The Great White belongs to the Lamnidae Family or mackerel sharks, which include mako and salmon sharks as well. An unique characteristic of the Great White is the ability to maintain parts of their body (swimming muscles and stomach) at temperatures above that of the surrounding water, which classifies them as endothermic or warm-blooded, like mammals.
Encounters
Great White sharks are found in all the cold or temperate coastal waters in the world and offshore waters of the continental shelf. Greater concentrations can be found in the southern coasts of Australia, in South Africa, California, Mexico's Isla Guadalupe and to a degree in the Central Mediterranean and the Adriatic Sea. They have also been seen in the tropical waters off Mauritius and in the Caribbean. The densest known population is found around Dyer Island, South Africa. Periodically it will wander into bays and harbours and will also inhabit waters around oceanic islands . Along the California coast, they can be found hunting near elephant seal haul-out areas from October through March. Though considered an open-ocean dweller (diving down to depths of 1280 meters), it frequently wanders into shallow waters, and even into surf zones. In North American waters, it has been reported from Newfoundland to Florida, and from Southeast Alaska to southern California. In Atlantic Canadian waters it is rare, but has been caught off Deer Island in the Bay of Fundy and off Campobello Island, New Brunswick.
Diet
Great Whites are an important predator of marine mammals, focusing mostly on elephant seals. They also feed on harbor porpoises, dolphins, other sharks, sea turtles and seabirds. They may also feed upon blubber from dead whale carcasses. Juveniles feed mostly on fish, switching to marine mammals once they reach approximately 454 kg. Fish such as salmon, hake, halibut, mackerel and tunas are common prey. A shark primarily uses its extra senses (i.e, Electrosense and Mechanosense) to locate prey from far off. Then, the shark uses smell and hearing to further verify that its target is food. At close range, Great Whites hunt their prey visually using their dark dorsal colors to help them blend in while cruising near rocky bottoms. Here they watch for unsuspecting seals on the surface above. When an acceptable animal is sighted, they accelerate quickly (sometimes breeching the water) and ram into the seal, stunning it, and at the same time take a large bite from the animal. They then return to feed on the carcass. Great Whites often receive considerable damage from their prey and as a result many have very large, visible scars. This is the only shark known to regularly lift its head above the sea surface to gaze at other objects such as prey . After one Great White makes a kill, others will come and feed off the same kill with no apparent aggressive interactions. The only animals known to attack them are other Great Whites and Orcas.
Reproduction
Very little is known about the reproductive cycle (live births have never been observed), however it is believed that Great Whites give birth to their live young in the warmer southern California waters. The young may then slowly migrate northward as they grow larger. Great Whites are Ovoviviparous which means eggs are retained within the body of the female in a brood chamber where the embryo develops, receiving nourishment from a yolk sac. The pups hatch from egg capsules inside the mother's uterus and are born soon afterwards. Females give birth to 4 to 14 live pups and may only reproduce 4 to 6 litters in a lifetime. White sharks reach sexual maturity at 10 to 12 years of age. Their lifespan has not been definitively established, though many sources estimate 30–40 years
Attacks
Many attacks on humans 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 (their only tactile organ) 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. Humans, in any case, are not healthy for great white sharks to eat because 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. More people are killed in the U.S. each year by dogs than have been killed by White sharks in the last 100 years. The great white is far more threatened by humans than we are of them.
Captivity
Great whites generally die in captivity after a few days due to their refusal to eat, or they are released back into the wild. It was not until September 2004 that the aquarium in Monterey Bay, California made history by becoming the first aquarium in the world to place a great white on long-term exhibit. The young female, who was caught off the coast of Orange County, was kept in the aquarium's massive 1 million-gallon Outer Bay exhibit for 198 days before her successful release back to the wild in March 2005. She was tracked for 30 days after her release.
Conservation
No accurate numbers on population are available, but populations have clearly declined to a point at which the great white is now considered endangered. Their reproduction is slow, with sexual maturity occurring at about nine years of age, such that population can take a long time to rise. The shark is targeted by fishermen for its jaws, teeth, and fins, and as a game fish. The great white shark, however, is rarely an object of commercial fishing, although its flesh is considered valuable.
Distinguishing Charachteristics:
- Serrated triangular teeth
- Lobes of caudal fin of about equal size
- Caudal keel
- Black spot may be present at axil of pectoral fin
- Lunate tail