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View Full Version : Week 12 - Great White Shark



Catiana
July 30th, 2007, 02:09 AM
In honor of Shark Week on the Discovery Channel, we visit the Great White Shark


Carcharodon carcharias
Great White Shark

Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Lamniformes
Family: Lamnidae
Genus: Carcharodon
species: Carcharodon carcharias

Description & Behavior

The great white shark, Carcharodon carcharias, aka white shark, white pointer, blue pointer, man-eater, manila shark, has, according to E.O. Wilson "...rightfully been called a top carnivore, a killing machine, the last free predator of man—the most frightening animal on earth." While this is a common perception of white sharks, some courageous explorers have not only free-dived with these "killing-machines," they lived to talk about it. Not that diving with white sharks is recommended, but these bold experiments have shown that these majestic, yet intimidating, creatures are not predators of men.

The great white shark is the largest known predatory fish in the sea. They reach lengths of over 6.1 m long and weigh up to 2,268 kg. They have a conical snout, pitch black eyes, a heavy, torpedo-shaped body, and a crescent-shaped, nearly equal-lobed tail fin that is supported on each side by a keel. The great white swims in a stiff-bodied, tuna-like fashion, unlike the sinuous whole-bodied swimming stroke of most sharks.

The name "white shark" is thought to have come from its universal all-white belly. The dorsal coloring of great white sharks, however, ranges from pale to dark gray and can vary tremendously depending on lighting and water color and visibility.

The great white's average length is around 3.6 m, but there have been reports of sharks as large as 7.62 m. The great white belongs to the Family Lamnidae (the mackerel sharks), which includes mako and salmon sharks. Along the California coastline, adult great whites are an important predator of marine mammals, particularly the calorie-rich elephant seals. Juveniles feed mostly on fish and add marine mammals to their diet when they reach about 450 kg.

White sharks are able to prey on such large creatures with their large upper teeth, which are triangular in shape and sharply serrated to cut large pieces of flesh from prey. The bottom teeth are narrower and not serrated and used to hold prey. An unusual characteristic the white sharks (shared by other mackerel sharks and thresher sharks, Family Alopiiidae) is the ability to maintain parts of their body (swimming muscles, stomach, and brain) at temperatures above that of the surrounding water, which classifies them as endothermic or warm-blooded, like mammals.

World Range & Habitat

Great white sharks have one of the widest geographic ranges of any marine animal. They are found in all cold temperate and tropical waters, from 60°N latitude to 60°S latitude. They were long thought to be primarily coastal inhabitants; however, from recent satellite tracking studies we now know that they migrate long distances, sometimes crossing entire ocean basins. Along the central California coast, they can be found hunting near elephant seal haul-out areas from October through March. Off the western cape of South Africa, they can be found near cape fur seal haul-outs from May to September. In North American waters, white sharks have been reported from Newfoundland to Florida, and from from the Aleutian Islands, Alaska to southern Mexico. Nowhere in its range is the white shark very common, and in fact, they are becoming increasingly rare.

Feeding Behavior (Ecology)

Recent research on interactions between great whites and various species of seals and sea lions suggests that great whites hunt their prey visually. Using their dark dorsal colors to help them blend in while cruising near rocky bottoms, they watch for unsuspecting seals on the surface above. When an animal is sighted, they accelerate quickly to the surface and ram into their prey, simultaneously stunning it and taking a large bite. They then return to feed on the carcass.

It should be noted that great whites often receive considerable injuries from their prey, many have been observed with deep scarring on the head from the teeth and claws of elephant seals and sea lions. It is still undetermined whether great whites are territorial; however, current observations indicate they seem to possess a home range. Recent research has shown that great whites exhibit complex social behavior that establishes rank among individuals. After one great white makes a kill, others sometimes come and feed off the same kill with no apparent aggressive interactions.

Life History

Very little is known about the reproductive cycle of the great white shark. Development is ovoviviparous. The smallest known free swimming white shark measured 1.1 m and weighed about 16 kg. Along the west coast of North America, 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.

Ovoviviparous: eggs are retained within the body of the female in a brood chamber where the embryo develops, receiving nourishment from a yolk sac. This is the method of reproduction for the "live-bearing" fishes where pups hatch from egg capsules inside the mother's uterus and are born soon afterwards. Also known as aplacental viviparity.

Gestation period is unknown, but may be longer than a year, after which mother Great Whites may take a year “off” before becoming pregnant again. Litter size ranges from 2 to 10 (possibly to 17) pups, each 1.0-1.5 m long at birth. Male great whites mature at 3.5-4.1 m in length and 9 to 10 years of age; females mature at 4-5 m and 14 to 16 years. Maximum lifespan is believed to be more than 30 years.

Comments

Although great whites have little commercial value, fishing for these sharks became a popular sport with big game fish anglers. The fearsome reputation of the great white has given it almost legendary status as an apex predator and they are often killed by humans for sport and for their jaws, teeth and fins.

Great whites are very curious and most so-called “attacks” appear to be motivated by curiosity rather than a desire to feed and most attacks on humans are not fatal. Ironically, the great white is far more threatened by humans than we are of them.

Great white sharks, Carcharodon carcharias, are now listed as Vunerable (VU A1cd+2cd) on the IUCN RedList of Threatened Species:


Because of the importance of this species as a key predator in marine ecosystems, the great white was granted protected status in 1991 in South Africa and in 1994 in California and Australia. Great white sharks are also an important species for marine ecotourism, observed by divers from the safety of cages in South Africa, southern Australia and Isla Guadalupe, Mexico.