Great white sharks (Carcharodon carcharias) have gotten a bad reputation for attacking humans. Contrary to myth and misinformation, great white sharks do not desire human beings as prey. To unravel the mystery behind how great white sharks capture their prey, scientists have examined what these sharks eat and experimented with how they attack their prey.
An immature great white shark does not have the higher metabolism an adult shark needs to keep itself afloat and active in temperate waters. Its food source tends to be rays, other sharks, and bony and cartilaginous fish. While an adult great white shark will eat these as well as mollusks, crustaceans, sea turtles, sea birds, sea otters, cetaceans like dolphins and porpoises, and cephalopods like squid, they favor pinnipeds like sea lions and seals.
A South African project which studies great white sharks and southern right whales have conducted experiments to understand the attack behaviors of great white sharks. They wondered why some sea otters and birds had injuries from their encounters with the sharks but were not consumed. What they discovered led to the conclusion that the first bite a great white shark took was to evaluate the fat and calorie value of the morsel in its mouth. Somehow the great white shark is able to determine if its prey is rich in calories and fat. If the prey is calorie and fat rich, the shark takes a powerful bite and allows the prey to bleed to death in a process called exsanguination. Up to fifty percent of the total body composition of a sea lion, seal, or elephant seal is fat, making these animals a favorite meal for adult great white sharks.
In the same study, square targets and inedible baits in the shape of swimming seals were used to determine if shape influenced the great white shark to attack. The shape that looked like a swimming seal was attacked. If the square target was the only bait dangled before the shark, the great white shark would explore the object by biting, then releasing, it.
Great white sharks do not travel in groups or even in pairs. When they have been seen in groups, they have been feasting on the carcass of a large whale. The great white shark travels alone. Usually the shark swims a short distance below the water’s surface. Its blue gray top colors camouflages it from any living thing which may be swimming above. Great white sharks have a mechanism called ampullae of Lorenzini in their heads. These are passages filled with a gelatinous substance which aids the shark in sensing minute electrical currents created by movement by other creatures in the water. Great white sharks can also sense a droplet of blood even when diluted in 25 gallons of water. They can locate a bleeding animal from three miles away.
Three methods of attack are utilized by great white sharks. The preferred way is to approach the prey from below until about one meter away and then increase speed to up to fifteen miles per hour while opening its mouth. Sometimes this lunge causes the shark to breach the water surface. The shark takes a bite to determine the food value of the prey. The shark will then either release the prey or will complete the bite and allow the prey to die from loss of blood. In the second method, the shark swims toward its prey with its dorsal fins above the water and quickens its speed when within striking distance. A much less common approach is when the great white shark comes up to its prey by swimming on its back.
In any event, once the prey is near death, the great white shark rips chunks from it with the first two rows of its three thousand sharp, serrated teeth. It then swallows the morsels whole. If the prey is an adequate meal, the great white shark may not have to kill again for up to two months.
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Sources:
http://www.enchantedlearning.com/subjects/sharks/species/Greatwhite.shtml
http://greatwhiteshark.netfirms.com/gwdiet.htm
http://www.oceanlight.com/html/great_white_shark.html several excellent photos of great white sharks
http://animals.nationalgeographic.com/animals/fish/great-white-shark.html
http://animals.howstuffworks.com/fish/great-white2.htm
