Myth: Why do sharks attack swimmers?

05 June 2018

Interview with

Adam Murphy

There's a common belief that sharks attack swimmers because they mistake them for seals. Is that true? Adam Murphy has been investigating this biting question...

Adam - Great white sharks can seem absolutely terrifying. “Jaws” was proof enough of that. They can be up to six metres long, weigh nearly 2000 kilograms, and can swim at 35 miles an hour. They are apex predators. Nothing goes near them. 

There's an idea floating around that sharks attack surfers and other swimmers unprovoked because to the shark it looks like a seal, and a seal looks like lunch. But that's probably not true, and the reasons why might be a comfort to you, or they might not. Is there a comforting way to be bitten by a shark? Sharks don't think we're seals. Sharks approach seals and other human-sized prey in a totally different way to how they approach us. Now while it's possible that sharks occasionally have cases of mistaken identity when they can't see very well, in open water when a shark hunts a seal it torpedoes itself towards the surface in a move called a breach. The shark rocket takes out the seal before the seal has time to think “hey what's that thing rushing towards me at tremendous speed?”

Meanwhile, sharks usually approach us calmly and quietly in comparison. Then, yes, they do take a bite but not for food. It's usually because they're just curious wondering what that thing in their backyard is, and they don't have hands to prod and poke something. Babies do that too. Need to understand what something is? Are you a baby? Put it in your mouth. So sharks are just like babies; giant, serrated tooth-filled babies. Isn’t that nice? And even if they were going to attack humans for food, we're really not worth the effort. Compared to blubber rich seals and sea lions we’re very boney things.

Research published in 2016 has shown that most of the bites inflicted on surfers and surfboards aren't strong enough to take out or incapacitate a seal. And sharks are very good at doing that. That idea is supported by Peter Klimley from the UC Davis College of wildlife fish and conservation biology and was supported by R. Aidan Martin, Former Director of the reef Quest Center for Shark Research in Vancouver, Canada before his death in 2007.

There is a theory that sharks will make an initial bite, swim off, and wait for the thing to bleed out. Well, they tend to use that for large prey. Elephants-seal-large, and we are not that large.

So unless they are desperate, they don't think we're seals and they want to investigate more than they want to hurt us. Sadly the sentiment is not returned. In 2013 humans were killing 100 million sharks a year, which is roughly two hundred every minute. That means the great white shark is now listed as vulnerable, and great whites can take up to 30 years to be able to reproduce making it that much harder for them to replace their population. Maybe it's time we start looking after them and stop being so afraid of them. We should probably do that before we seal their fate.

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