Are unprovoked shark attacks becoming more common?

Tiger shark Tiger sharks tend to be very cautious

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Sharks have again made the headlines for all the wrong reasons.

On Tuesday a British man, Ian Redmond, was fatally attacked by a shark while he was snorkelling in the Seychelles in the Indian Ocean.

It was the second fatal attack by a shark in the area this month.

But are shark attacks becoming more common, and are more swimmers and bathers dying as a result?

According to the International Shark Attack File (ISAF), a program run by marine biologists at the Florida Museum of Natural History, the number of unprovoked shark attacks has grown at a steady pace over the past century with each decade having more attacks than the previous.

For example, in the 1900s there were, worldwide, around 20 recorded unprovoked attacks by sharks on people.

That steadily climbed to around 100 by the 1940s, passing 500 by the 1990s. By the 2000s the figure had surpassed 650.

Expert View

  • Having dived with some 40 species of shark, including some of the biggest and scariest, I've come to the conclusion that almost every attack can be explained through understanding their natural behaviour.
  • Sometimes the shark simply makes a mistake: swimming in poor visibility and looking like a seal is not a good idea if there's a great white around. Sometimes we give off cues that stimulate an attack, such as wearing flashy jewellery or by splashing erratically, simulating prey in distress. Sometimes it's the introduction of another factor in the shark's environment, such as effluent, fish blood or even the sudden arrival of a competitor - another shark perhaps.
  • To understand what occurred in this latest tragic incident we have to first be sure what species the shark was. The most likely candidates from the dozen or so species commonly found in the Seychelles would be a tiger shark, a bull shark or perhaps an oceanic white tip.
  • Given the attack occurred in shallow water, it's less likely to be an oceanic white tip - as its name suggests it's more of an open water species. I've worked with tiger sharks in shallow tropical water and know them to be generally very cautious, so it seems at this stage that the culprit is most likely to be a bull shark. Bull sharks have a reputation for making attacks in shallow water. They are a broad, sturdy shark and, in the Seychelles, can grow to some three metres long. One bite will strip muscle from bone or even remove a limb entirely.
  • Initial reports suggest that Ian Redmond tragically suffered multiple injuries. This suggests a repeated attack - which is highly unusual. Sharks usually realise their mistake on the first bite and back off, which is why most shark attack victims survive.

But in many respects, this data is misleading.

The ISAF is the best current data set for shark attacks we have, yet by its curators' own admission, this rising tally of recorded unprovoked attacks does not actually mean that sharks have in any way gained a greater taste for humans, or are attacking them at a greater rate.

That is because the media and scientists paid far less attention to shark attacks in the past than they do now.

In 1916, people along the coast of New Jersey, US were gripped by panic as a spate of shark attacks occurred in quick succession between July 1 and July 12.

The national media descended on the area to report the attacks, which killed four people and injured another. Scholars to this day debate which shark species was responsible, with a bull shark or great white being most often blamed.

But those attacks created an exceptional media storm. Most attacks went unreported and data about them was not systematically and objectively collated.

The ISAFs own records show a dip in the number of attacks occurring during the 1970s and 80s. But that, says the ISAF, is more likely due to the fact that the organisation itself didn't keep as complete records as it did before and since.

Other factors have changed too, and must be taken into account.

The human population has grown rapidly in the past century, meaning many more people are taking to the water, and engaging in recreational activities for longer periods that put them in closer proximity to sharks.

Florida has the most unprovoked shark attacks recorded anywhere in the world. The state's increase in shark attacks, from a handful in 1900-10 to around 190 in 2000-10, mirrors almost exactly the decade by decade increase in the numbers of human residents, from 1 million to more than 16 million today.

California, Japan and Hawaii show a similar trend. In Australia, there are no more attacks today than there were in the 1920s, 40s or 50s, and actually far less than in the 1930s or 1960s, despite the human population rising from 4 million to more than 18 million.

Great white shark (image: Great white sharks attack the most, if records are accurate

Another interesting statistic is that while recorded attacks have steadily climbed each decade, the proportion of people dying as a result has fallen consistently across the same period.

In the 1900s, 0.6% of unproved shark attacks on people proved fatal. By the 1960s that had fallen below 0.2% and today less than 0.1% of victims die as a result of an unprovoked attack.

There are likely to be many reasons for this decline; modern surfboards and diving gear get bitten rather than their owners, while victims reach vastly improved medical facilities much sooner.

Even identifying which sharks are most likely to attack is notoriously difficult.

Great white sharks get the most blame. This species, one of the largest of the predatory rather than filter-feeding sharks, has been recorded attacking unprovoked 182 people, killing 65.

Tiger and bull sharks, a species that can frequent fresh and salt water, have similar statistics, both having attacked around 60 people, each species killing around 25.

Tips to avoid an attack, by James Honeyborne

Here are some truths about shark behaviour gleaned from 20 years making wildlife films, that may help put the odds on your side:

  • Sharks are generally cautious predators. Swim with a buddy - don't swim alone as they are less likely to approach a group.
  • Sharks are visual hunters - don't swim when their vision is compromised and mistakes can be made: avoid dawn and dusk, or swimming in murky water.
  • Sharks are attracted to bright objects: don't wear shiny jewellery, reflective watch-faces or high contrast clothing that might be mistaken for their flashy prey.
  • Sharks sense panic. Swim efficiently and minimise splashing and erratic movements. If a shark turns up, keep calm and confident and leave the water. Keeping eye-contact with some sharks will make them reluctant to approach. Never turn your back on the shark.
  • Sharks communicate visually. You can often tell a shark's disposition by its body language. An aggressive shark accentuates its body posture. A relaxed shark looks languid. Remember they are all opportunistic however and can change their mood very quickly.
  • Sharks can be aggressive. Never antagonise a shark or allow it to feel threatened. Equally, don't let it dominate you. If you're in its world, give it the respect it deserves. If a shark looks grumpy, get out of the water.
  • Sharks prefer some places to others. More sharks hang-out near steep drop-offs, for example. Avoiding areas known for sharks to congregate seems wise, unless of course you're a wildlife film-maker seeking out an encounter.

But victims or onlookers are rarely able to accurately identify which shark species actually attacked, which is unsurprising given the stress of any attack and the speed at which it happens.

That means even these statistics must be treated with caution.

They are likely to be skewed toward more easily identifiable species, such as great whites, tiger, hammerheads and nurse sharks.

But a range of species have also attacked people, including sandtiger sharks, blacktip sharks, narrowtooths, blues, shortfin makos and even wobbegong sharks.

Tooth remains are seldom found in wounds, and according to the ISAF even trained professionals find it difficult to tell which species caused a particular bite, especially among the requiem shark species belonging to the genus Carcharhinus, which include bull sharks, oceanic whitetips and many others implicated in attacks.

If more of these sharks were accurately identified after an attack, then species such as hammerheads would get pushed down the list of those which attack people most often.

"Nonetheless," says the ISAF, "the white, tiger and bull sharks are the 'big three' in the shark attack world because they are large species that are capable of inflicting serious injuries to a victim, are commonly found in areas where humans enter the water, and have teeth designed to shear rather than hold."

However, overall, the tally against each species remains small, especially relative to the large number of interactions significant numbers of individual sharks have with swimmers and divers.

Sharks, it seems, are not attacking people at a greater rate than in the past.

It's just that more people are getting into the water with sharks. And the more frequently we do so, the greater the likelihood that attacks will happen.

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