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Why do white sharks bite people?

Photo © Thomas P. Peschak, Chief Photographer, Save Our Seas Foundation. Photo by © Thomas P. Peschak

Several theories have been put forward by experts as to why white sharks sometimes bite people. In this article we examine three of the most prominent theories and look at why most of these incidents are non-fatal.

Firstly it is important to realise that shark attacks are far more rare than many people might expect. According to the International Shark Attack File there have been an average of just over 60 shark attacks per year worldwide over the last decade. However, on average, less than 5 people per year die from these attacks – so the overwhelming majority of shark attacks are non-fatal. Considering the amount of people who use beaches every year these numbers represent a relatively small risk to the average beach-goer, compared to say driving a car, where according to the World Health Organisation 1.2 million people are killed annually in road accidents.

Sharks have wandered our oceans for the past 400 million years, at least 200 million years earlier than the dinosaurs and 396 million years before the first hominids evolved. At the beginning of the Jurassic period, about 200 million years ago, the first ‘modern’ sharks developed. Smaller sharks and other fish as well as marine mammals joined great white sharks on their journey through time and as these evolved in the water beside them they became their natural prey.

Though we humans may be fascinated by the ocean and endeavor to extend our natural limits in or on it through the use of modern technology, it is not our natural habitat. We did not evolve alongside sharks and hence they do not recognize us as their natural prey or part of their diet.

White Shark Beach Photo by Enrico Gennari / © Alison Kock

So why do sharks bite people and why are most of the attacks non-fatal? Here are some of the main theories put forward to explain what might be happening.

1: Investigatory theory
White sharks are intelligent and curious apex predators with complex behaviour patterns. They sit at the top of the marine food chain, and although they are hunted by man, they have no natural predators. As a result white sharks, especially the larger individuals, are confident in nature and extremely curious. They are much more likely than other marine species to investigate unknown objects in or on the water. Unfortunately, when they are unable to identify an object they rely on an investigatory bite to gather more information. White sharks don’t have arms like we humans do and so their mouths are their best exploratory tool when it comes to up-close investigations. White sharks are known to have ‘tasted’ a variety of animals and objects, including seabirds, kayaks, boats, plastic bags, and paddle skis.

2: Mistaken identity theory
A shark is able to sense a person in the ocean long before that person can detect a shark. White sharks have excellent senses. They can detect sound and pick up smells from hundreds of metres away. They can sense moving objects through their lateral line, which consists of pressure-sensitive receptors along their body, and their vision underwater is far better than ours. However, these senses, impressive as they are, are not perfect. A large number of attacks occur when water conditions are poor leading many scientists to believe that bad visibility, background noise from heavy surf, and other conditions can cause white sharks to mistake humans for their normal prey.

3: Social / defensive theory
White sharks defend their ‘personal space’ by communicating through body posturing and biting, and the less dominant shark is normally forced to give way to the more dominant. A surfer or swimmer at the surface, totally unaware of a shark’s presence below the water, would be unaware of a shark defending its space until bitten. A shark could even view a person as a competitor when fish or other prey is in the water.

So we see that there are a number of reasons why a white shark might “attack” a person, although these seem less like attacks and a lot more like accidents. Especially when most of the incidents tend to be non-fatal.

Some researchers believe that in the initial bite a shark can detect the calorific value of its potential prey, informing the shark through the ratio of fat to bone or muscle whether its mouthful is worth eating or not. This could explain why in many cases the white shark has bitten lightly and let go, as the initial contact with its taste buds sends clear signals that a human is not prey, particularly if the swimmer or surfer is wearing a wetsuit. It is extremely rare that a white shark bites a human and continues feeding. Most of these incidents involve bites of minimal force and this could account for why there are so many more non-fatal shark “accidents” than fatal ones.