Why do sharks bite people?Science communicator
You’ve come here because you want to know why sharks bite people, and it’s a great question! Before we get to some potential answers, let’s unpack a few important facts to keep in mind when you read about shark bites.
Which sharks bite people?
In order to better understand your risk of being bitten by a shark, it’s important to take a look at the shark family tree. Only about a dozen of more than 500 known shark species have ever fatally injured a human. Sharks are vital to the health of the oceans and most of them pose no threat to humans whatsoever.
The dwarf lantern shark, for example, is small enough to fit in your hand. At the other end of the spectrum, the biggest fish in the sea – the whale shark – would struggle to swallow a grapefruit. Despite their impressive size, whale sharks are harmless filter feeders whose teeth and throats are built for slurping down plankton and other small prey.
To be considered a potential threat, a shark must be predatory and longer than roughly 1.8 metres (six feet). It’s these sharks that have teeth and jaws of the right shape and strength to inflict a significant injury. Just three members of this group – the white shark, tiger shark and bull shark – are implicated in the bulk of shark bites on humans. But even such cases are far more rare than you might expect.
How often do sharks actually bite people?
According to the International Shark Attack File, which is a comprehensive database of shark bite cases that have occurred between the 1500s and the present, between 70 and 100 people are bitten by sharks each year. In most of these cases, the bites are not fatal, and many of them cause only minor injury.
Humans also have a hand in a large percentage of shark bites. Of the 96 bites recorded in 2020, just 57 were unprovoked, meaning the person bitten didn’t initiate contact with – or harass – a shark before being injured. And of those 57 unprovoked bites, 10 were fatal.
Media reports often highlight ‘spikes’ in shark-related deaths, which can paint a scary picture. But these fluctuations are normal and do not necessarily indicate a pattern or trend. Many factors, including changing weather and ocean conditions or socio-economic shifts (which affect the number of sharks and bathers in a given area) can influence how many people are bitten in a given year.
Long-term trends show a decreasing number of shark bite fatalities per year. And while the average number of shark bites goes up each decade, there is no evidence that there are more shark bites per capita. What this means is that as our population continues to grow, the number of people bitten by sharks is likely to grow too. But it doesn’t follow that the risk of being bitten is higher for an individual person. There are just more of us spending time in shark habitat.
How do the numbers stack up?
There are more than 7.6 billion people on earth and about 40 per cent of that population lives within 100 kilometres (60 miles) of the coast. Remember that just 10 people were killed by sharks in 2020. While every shark-related death is tragic, the risk sharks pose to human life is exceedingly low. In fact, bees and wasps are responsible for more deaths each year.
Between 2004 and 2013, sharks killed eight people. During that same period, officials launched more than 300,000 rip-tide rescues. Every year, an estimated 236,000 deaths by drowning occur around the globe, along with over 1.3 million fatal traffic accidents. Indeed, drives to and from the beach pose a bigger threat to your life than sharing the water with sharks. So do lightning strikes, power tools and sand holes! More people are hospitalised annually for sunburn, dehydration and jellyfish stings than for shark bite trauma. More sutures are used to stitch cuts caused by seashells.
Why do sharks bite people?
Several theories have been put forward by experts as to why white sharks sometimes bite people.
What we can say for sure is that sharks do not bite humans because they want to eat them. These animals have cruised the world’s oceans for more than 400 million years. Sharks were searching for prey 200 million years before the dinosaurs showed up and 396 million years before the arrival of our most distant hominid ancestors. Humans have never been sharks’ natural prey and we can see that in the way they bite.
White sharks and many of their predatory cousins have teeth built to shear, not grip. It’s that dental toolkit that helps large sharks to take bites out of tough prey like seals, sea turtles and dead whales. It also means that a bite on a human can do significant damage. And yet, most white shark bites are not fatal. The cause of death in the overwhelming majority of shark-related fatalities is blood loss.
Save Our Seas Foundation project leader Dr Alison Kock notes that some researchers believe sharks can detect the ‘value’ of prey during an initial bite. ‘This could explain why, in many cases, a white shark has bitten lightly and let go,’ she says, noting that most white shark incidents involve bites of minimal force.
Imagine chomping into a sandwich. Now imagine taking a bite of two pieces of bread with nothing between them – you’d be able to tell the difference. Sharks may pick up similar cues, like the ratio of muscle, to fat, to bone in a potential meal. Perhaps, explains Kock, ’the initial contact with [the shark’s] taste buds sends clear signals that a human is not prey, particularly if the swimmer or surfer is wearing a wetsuit’.
Most shark bites occur in near-shore waters, where sharks are most likely to come into contact with bathers. But many of their favourite menu items – animals like stingrays and other fish, as well as seals – also gather in those areas. Man-eating ‘rogue’ sharks make good TV villains, but there is no evidence to support the idea that any sharks patrol beachfronts for human prey.
Large sharks like white sharks, bull sharks and tiger sharks are highly migratory; they don’t stay in one place for long. In fact, there are only a few cases in documented history where a single shark might have bitten several people in one area, and the jury is still out on each of them.
If sharks don’t bite people with the intention of eating them, why do they bite people at all? One reason might be curiosity. Sharks don’t have hands, so they rely on their sensitive mouths to gather information. The sharks that bite humans most often sit high in the food web. Because they don’t have to worry about being eaten, they’re often curious and confident, and they’re more likely than other marine species to investigate unknown objects in the water. Sharks have been known to ‘taste’ test – and subsequently spit out – everything from cameras to boats, to plastic, to seabirds.
Some shark bites may come down to a case of mistaken identity. While sharks have an arsenal of super-sensing abilities, those senses are not perfect. A large number of bites occur when water conditions are poor, which could indicate that factors like low visibility and background noise from heavy surf make it harder to distinguish prey from non-prey. Activity like splashing and paddling may add to this confusion. What’s more, sharks may mistake people for competition in some cases, particularly when fish and other prey are nearby.
It’s also possible that some bites are the result of a shark defending itself. While sharks aren’t the indiscriminate aggressors they’re made out to be, they are wild animals that should be respected. Many sharks give warning signs to other individuals through body posturing. If those ‘back off’ signals fail, the next step is to bite. A surfer or swimmer at the surface, totally unaware of a shark’s presence below the water, would not be privy to those warnings.
I understand that shark bites are rare, but I’m still scared. What can help?
If you’ve swum in salt water before, chances are you’ve been closer to a shark than you realise. If that gives you more anxiety than comfort, don’t beat yourself up. Fear is important; it helps to keep us safe. When it comes to sharks, however, it’s also important to think about how decades of films, television, novels and news stories have shaped perceived danger.
One of the best ways to tackle your fear of sharks is to keep learning. The unknown is scary, so get to know sharks! Dive into their Incredible diversity, warning signs and behaviour and the many roles they play in keeping the ocean ecosystem balanced and healthy.
Learning about the sharks in your area can also help you to stay ‘Shark Smart’. Knowing which sharks you might encounter, why and when they spend time nearby and how to behave if you bump into one will help ease your mind. It’s always a good idea to avoid water where seals, running bait fish and other common prey species congregate. Pay attention to postings and warnings and avoid swimming or surfing when water conditions are poor. If you encounter a shark, do not feed or touch it.
In reality, we pose a far larger threat to sharks than they do to us. It’s estimated that as many as 100 million sharks are killed by humans each year and many shark species already face the threat of extinction. While overfishing presents the biggest threat, increased human activity, pollution, habitat destruction and the impacts of climate change all affect shark populations. And remember, we’re better off when those populations are thriving. What makes sharks so important? Find out here!
Nicholas K Dulvy, et al., Extinction risk and conservation of the world’s sharks and rays, eLife.
World Health Organisation, 2021, Drowning
World Health Organisation, 2021, Road traffic injuries
Florida Museum, 2018, Shark attack compared to other risks
Florida Museum, 2018, Shark Attacks vs. Population Growth
Florida Museum, 2020, Species Implicated in Attacks
Florida Museum, 2018, Beach Attendance
Florida Museum, 2021, Yearly Worldwide Shark Attack Summary
Florida Museum, 2021, Shark Attacks in Perspective
David S. Shiffman, 2013, World’s largest group of shark scientists calls on AP and Reuters to resist using the phrase “shark attacks”, Southern Fried Science.