18 Jul 2012 0 Share

Jock Serong

Senior Writer

Why shark attack statistics tell us so much, and so little

By Jock Serong

The media cycle played out again over the weekend: the footage of helicopters at a beach, boats circling endlessly, and the painful sight of photos supplied by the family: in this case a smiling kid in a wetsuit who looked much like anyone else you’ve nodded to in the carpark of a surfbeach. Someone’s son.

Shark attacks are every bit as traumatic as road accidents, but we’re nowhere near as accustomed to them. Young people in particular are fatalistic about road trauma, which is why they drive fast and send text messages and do dozens of other foolish things behind the wheel. But no-one is blasé about the prospect of being ripped to pieces by a wild animal. It’s highly emotive territory, and even cold hard statistics do little to cut through the dread.

The Australian shark attack file is a database covering the 700-odd shark attacks in Australian waters since 1791. It’s maintained by Taronga Zoo in the interests of providing objective data for research. The ASAF’s John West, who curates all that information, estimates that there are 100,000,000 beach visits each year in Australia, along 35,000 kms of coast.

Yet shark attack fatalities tick along at a steady rate of around one per year, despite our population and visitor numbers increasing all the time. According to the ASAF, 28% of attacks in Australian waters, a little over one in four, are fatal. And that ratio of deaths to attacks is falling, as it is all around the world, most likely due to better medical care. Considering the sheer number of dangling legs along our coast at any given time, it is reasonable to call the fatal attacks freak occurrences.

Breaking the numbers down a little further, in the last twenty years, there have been twenty-five fatalities, which averages out to around 1.25 per year. In the last fifty years, there have been forty-six fatalities, averaging less than one (0.92) per year. Therefore, there is substance to the idea that attacks are on the rise - it’s just that it’s a statistically tiny increase. The same thing can be demonstrated when looking at non-fatal attacks: from an average of 6.5 incidents per year in 1990–2000, these are now occurring at a rate of 15 incidents per year over the past decade. But the explosion in participation in watersports over this period dwarfs the increase in attacks.

Surfers are by far the most heavily represented group among victims: they are attacked at nearly three times the rate for swimmers, and five times the rate for divers. According to research work done by John West, there has been “a 310% increase in attacks on surfers since 1999. There have also been substantial increases in the attacks on swimmers, SCUBA divers and sailboarders.”

Perversely, we tend to look for anomalies which will make the statistics feel unsafe. We search for patterns to give gravity to terms like “shark infested” and “man-eater”. If attacks happen close together, whether in time or physical location, there’s talk of how far one shark can move in a day, as though an individual animal has gone rogue and taken victims at multiple beaches like a serial killer. 

Fear has the upper hand over mathematics again: this time due to a remarkable cluster of attacks in W.A. There's been six attacks in the last 12 months, five of them fatal, in the 300km stretch between Lancelin and Busselton. Of those, five were within 200km and nine months of each other. Five were outside the "cricket season" months when attacks are usually concentrated, and in fact the last couple have been deep within winter. What does it all mean? 

Kent Stannard of the research funding body Whitetag makes the point that sequences of attacks are not unprecedented. “S.A. had a similar run of fatalities back in the early 2000s,” he says. “Just because shark numbers appear to be high in one area doesn't mean they are high elsewhere. The Neptune Islands have a shark index which goes in peaks and troughs - some years high shark activity, some years low. Dangerous Reef in the Spencer Gulf was consistently the site of most white shark activity back in the 70s and the 80s.We went out with the Fox group late last year dropped off acoustic receivers and returned in April this year to find only one tagged shark had been in the area over that period.”

Would a mathematician tell you these peaks and troughs are within the bounds of normal statistical variation? Or does the WA cluster give credibility to concerns that great whites are becoming more numerous in southern WA, or that something about their diet or habitat is changing, to bring them inshore? Seal and whale numbers along our coast are known to have increased over the last decade, but conversely, the impact of our fisheries is greater by the year. 

On a recent shark tagging trip with Barry Bruce, the CSIRO’s chief researcher of great whites, I remember raising these questions and being told that no-one knows how many great whites are out there. There is simply no way of counting a solitary wild animal in an unwatchable environment. So we protect them on the precautionary principle that if it’s likely we are pushing an animal towards extinction through the combined effect of our actions, we should assume the need for protection. As he told me this, Barry Bruce and I were sitting on a rented fishing trawler, filling the water with pungent burley in a known nursery area. We’d been at it for six hours, and hadn’t seen a fin.

But in the wake of Ben Linden’s tragic death last weekend, there’s talk of lifting the ban on commercial and recreational great white fishing, and specific orders have been given by the state fisheries minister to exterminate all four to five metre sharks in the area. It is unclear from the relevant press release exactly what constitutes “the area”, and whether officers should measure sharks - to establish guilt by body length - before shooting them. The scientific consensus is that such killings are politically effective but practically useless. Even if every large shark off Perth is caught, killed and dissected until human remains are found, the exercise has all the scientific rigour of a witch hunt. There is no research basis for the idea that sharks involved in one attack will go on to attack other humans. On the contrary, it is believed that in the majority of cases sharks immediately leave the area and don't return. 

According to Kent Stannard, “Australian salmon are in abundance inshore along the southern coasts at this time of year and migratory species - including white sharks - are working their way up the east and west coasts of Australia. White sharks when migrating are in transit mode, and behave differently than at seal colonies. They tend to be opportunistic feeders. This, mixed with more surfers and ocean users, suggests chances of interaction are heightened.”

Tagging is beginning to provide the data that might ease our minds. Movement patterns, residency times, site fidelity and behaviour can now be measured and plotted. But it’s expensive, time consuming work, and it’s a lot less sexy than a mass killing. It matters, because the more tags are out there, the more accurate the data becomes. As long as good quality information is finding its way to the broader ocean user community, then it can be said tagging is potentially saving lives. Stannard gives the example of a 5m tagged white shark triggering the receivers off Perth beaches recently: the signal gave surf lifesavers time to activate their shark response plan. “This shark was tagged down near Albany,” he says, “which also confirmed these animals are a migratory species moving up and down the WA coast at certain times of the year.”

“CSIRO research has identified an eastern seaboard population of white sharks all stemming from and returning to the one region in eastern Bass Strait,” he continues. “These sharks all share the same genetic code, and they track between Wilson’s Prom and the Port Stephens region of NSW. All are considered juveniles - 1.2 - 2.8m, and 1-5 yrs of age. When they return to eastern Bass Strait, they don't go beyond Wilson’s Prom. It’s possible that’s genetically hard-wired in them.”

We’re in the early stages of what might be achieved by tagging and genetic coding. The risk of shark attack could be dramatically lowered through scientific intervention. But in the meantime, an average of 87 people are drowning at Australian beaches every year. Just plain old drowning. These deaths are not as gruesome, but in many cases they’re far more preventable. For the cost of a national shark cull, for the environmental damage it would do, how many sharks could we tag? How many kids could we teach to swim? How many more beaches could we patrol? This is the delicate dance of numbers, so easily skewed by fear.

Tags: jock , serong , THE TEETH OF THE GREAY WHITE DEBATE , great whites , great white sharks , great white , great white shark , shark , sharks , whitetag , Ben Linden , CSIRO (create Alert from these tags)

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