"This shark..swallow you whole." We've all heard the line from the 1975 horror thriller Jaws. The film rocked the world and threw the Great White Shark (Carcharodon carcharias) into the public eye like never before. In the 30 plus years since the release of Jaws the white shark has been identified as a man-eating machine. A shark that prowls the ocean, taking a bite out of anything and everything that it comes across. According to popular belief a white shark will seek you out and tear you to pieces should you dare venture into the sea. When in reality, nothing could be further from the truth.
The Great White Shark is an apex predator. It is at the top of the food chain. They have no natural enemies and are not preyed upon by any other creature in the sea. The shark's only enemy is humans, who kill hundreds of thousands of sharks every year. Contrary to what many would like to think, the great white is a complex and elusive fish that has a very specific and picky diet. They begin life feeding on small fishes, rays and other sharks in addition to scavenging on animal carcasses. This allows the juvenile shark to hone its hunting skills on smaller prey that is less likely to injure the shark in a struggle. As they mature, white sharks slowly switch their diet to larger prey in the form of elephant seals, sea lions and small toothed whales. Although, even as an adult the white shark will continue to scavenge on carcasses if the opportunity arises.
White sharks prefer a prey that has a thick blubber layer, as they normally inhabit colder waters it is not worth expending the energy on a kill if they are not going to get a good amount of energy-rich food from it. The white's attack strategy starts with smell and sound. The white shark will cruise along at the floor of the ocean and look for potential prey on the surface; they will also "listen" for any sounds of struggling or injured animals. All animals emit an energy signature, and the shark can sense this. A struggling or dying animal will emit higher frequency sounds, exciting the shark to a potentially easy meal. Once they spot potential prey, it is not uncommon for the shark to make a few passes a bit closer to it, just to determine if it is something they are interested in consuming.
Once the shark has decided that it wants to attack, it will drop back to the bottom and swim at the highest speed it can manage toward its prey. A few seconds before the attack, the shark will roll a third eyelid (nictitating membrane) over its eyes and continue on smell and sound alone. This is to prevent a struggling seal from injuring the shark's eyes, but can also lead to disaster if the "prey" turns out to be a human. Once the shark inflicts its first devastating bite, the shark will usually back away and allow the animal to bleed to death before consuming it. This attack method uses the least amount of energy and contains the least risk of injury, in addition to providing the greatest reward for the shark.
Unfortunately all of these things working in conjunction make it a bad day for a human in the area of a hunting shark. It is possible that an erratic swimmer could excite the shark as a possible meal. The shark then decides to bite, and comes away with a mouthful of bone instead of blubber and will usually leave. Unfortunately the damage is already done. Thankfully, most white sharks bites on humans are not fatal. In fact the percentage of fatal attacks by white sharks are considerably less than most other shark species. It appears that white sharks will occasionally make a mistake when biting a human being, believing that we are just another large marine mammal. Or, on occasion, the bite is a mild one that is meant only to investigate. Sharks do not have hands, so cannot touch something to find out if its edible. They have most of they're nerves and sensory abilities in their mouths and bite to investigate and "touch" an object. But for us humans, those investigative bites are equally devastating even if the shark decides we are not on the menu.
As you can see, the great white shark is an advanced and complex predator. But it is not the killing machine that many would like to believe. They have a very specific diet that rarely, if ever, includes us. They use their millions of years of evolution to their full advantage in order to ensure their own survival. As long as we can keep from appearing like prey, our chances of being mistaken for such are slim.