by P.L. Hubble

Created on: January 29, 2009

The Great White shark, scientifically named Carcharodon carcharias, is the breed of shark that comes to mind whenever we think of shark attacks. The movie "Jaws" is mostly responsible for this. In reality, there have only been about 250 shark attacks reported in almost 150 years. Those are excellent odds for the ocean swimmer. The Great White can grow up to 7 meters long, although the average length is closer to 10 feet. A shark uses cartilage for it's skeleton, which doesn't preserve like bone. As a result the only fossil records of sharks are their jaws and teeth.

A GW uses two main senses to hunt its prey. The first is the sense of smell. Two nostrils are near the end of the snout, and since the gills do the breathing, the nostrils only function is to smell. Inside the nostrils are many sensor organs called lamellae which are each covered with millions of olfactory cells. This makes the shark into a mobile nose, able to sniff out blood at long distances. The second sense a GW uses to hunt with is a very unusual and specialized. Again on the snout of the GW are many markings called ampullae of Lorenzini. Each is a capsule filled with a substance excreted by the shark which is sensitive to electrical discharges. Every creature in the ocean emit's a small electric field where their skin meets the water. Since the mouth and gills are covered with a mucous membrane, an electric field is generated according to their breathing pattern. Last, but not least, a bleeding creature emits even more electricity. This allows the shark to differentiate between prey that are moving naturally and those in a panic. Combined with the sense of smell, this sense makes the Great White an almost perfect predator for its environment.

The Great White is an apex predator, meaning it is at the top of the food chain with no natural predator. GW sharks will eat almost anything in the ocean, including fish, squids, other sharks and whales. However, their favorite meals are seals and sea lions. Studies have revealed that sharks seem to adjust their attack pattern according to the type of prey they are hunting. An example of this is the seal, which the GW sharks seem to like attacking from behind and just under the surface. With the sea lion as prey, the sharks seem to prefer attacking on the surface, often throwing itself out of the water in a savage attack. Nearly every attack observed has been from below, leaving the only avenue of escape towards the surface, exactly what the shark prefers. It seems that most attacks occur during the day in late summer and early winter. The attacks seem to follow a schedule according to the rise and fall of the tide.

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