A Time to Kill?

The fatal shark attack off western Australia at the weekend was the fifth such incident in less than a year.

The death of surfer Benjamin Linden, 24, who was apparently mauled by a large white shark, has sparked concern among government officials and prompted calls for the animals’ protected status to be lifted.

But are unprovoked attacks really rising in the region, and, if so, what might be behind such a trend?

Dr Bob Hueter, director of the Mote Marine Laboratory’s Center for Shark Research in Sarasota, Florida, cautions against jumping to conclusions.

He told BBC News: “When you have multiple attacks, it can be one of two things or a combination of both. The most obvious is that there are more sharks there in a place where people frequent for some reason.”

Dr Hueter pointed to the example of Cape Cod in Massachusetts, where great white sharks are increasingly coming close to beaches popular with bathers because conservation efforts have caused populations of seals – which the sharks prey on – to rocket.

“The other factor – which is often the most difficult one to understand – is just this concept of statistical clustering,” he explained.

“Because you get two events that seem to be close together in time and space, doesn’t mean you’ve got a trend.

“That’s what the media often doesn’t get, as soon as you get a couple of these together they’re talking on the evening news about an increase in this, or an increase in that. And that’s just not necessarily the case.”

The death on Saturday of Mr Linden has re-ignited a debate on lifting the protection afforded to great whites, to allow either fishing or a cull.

After the last fatal attack in March, state premier Colin Barnett ruled out a culling programme, saying it was impossible to protect all people at all times.

But talking to Australia’s ABC television, fisheries minister Norman Moore said: “I think we need to have another look now to see whether or not there’s been a significant increase in great white numbers since they became protected. And if that’s the case, should they still be on a protected list?”

He suggested researchers look at whether there had been an increase “commensurate perhaps with an increase in the number of whales going up the coast, a number of seals that are also protected – which are food for great white sharks.”

Rare occurrences

Sharks are common in Australian waters, but fatal attacks remain rare, averaging about one a year over the last two decades.

John G West, curator of the Australian Shark Attack File, pointed out that there were an average of 87 drownings per year on the country’s beaches.

“People should be more concerned with swimming at a beach than being killed in a shark attack,” Dr West, who is based at the Taronga Conservation Society in New South Wales, told BBC News.

He added: “For the last 100 years there have been as many as five occasions where there have been over 10 shark attack fatalities and eight occasions where five fatalities have occurred over a two year period. The events in Western Australia over the last two years are unusual in that they occurred in the one State.

“What is known is that white sharks in particular do swim along the Western Australia coast at various times of the year on their way between feeding and possibly mating grounds.

“They have been doing this for millions of years. The ‘path’ they travel brings them in close contact with the shoreline and in some case with people in the water.”

Last year, Dr West published a scientific paper showing that the total number of shark attacks in Australia has risen from about 6.5 incidents between 1990 and 2000 to 15 incidents per year in the last decade.