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17 January 2011

Shark attacks on the increase?

There seems to have been a steady increase in shark attacks in South Africa's waters, but is it the fault of humans or sharks?

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A young provincial surfer, Zama Ndamase (14), died in Port St Johns on Saturday when he was attacked by what is presumed to be a Zambezi shark. Are shark attacks on the increase?

Shark attacks are way down on the scale of health risks facing the average person (even surfers and divers). That’s cold comfort to victims of shark attacks and their families, but the point that shark conservationists and scientists frequently make is not that sharks aren’t dangerous – rather that they have been unfairly ‘demonised’.

The so-called ‘increase’ in attacks is really a public perception fuelled by media hype, says Leonard Compagno of the South African Museum’s Shark Research Centre. Your chances of being attacked by a shark, Compagno points out, are very low. This doesn’t mean people shouldn’t be cautious, but there are other far greater dangers to worry about in the ocean – drowning, for instance.

According to Geremy Cliff, head of research at the Natal Sharks Board, although the numbers of attacks in KwaZulu-Natal have actually decreased, in the Eastern and Western Cape they have increased slightly over the years. The national average now stands at about four or five a year. Some years do exceed this, says Cliff: “In 1998, there were 18 attacks. But not all are fatal.”

Humans on the increase
But when increased numbers of shark attacks occur, it may be because of changes in human rather than shark behaviour. There are more people taking up salt-water sports like surfing and spear-fishing, and people may be taking more risks in the water.

“When you think of the thousands of people swimming off our beaches, the shark attack figures are really very low,” says Cliff. “The increase in attacks may simply be because there are more people in the water. Also, there are more surfers these days than in the past, and they’re able to stay in the cooler waters for longer because they have better wetsuits. Most of the attacks we’re seeing happen to people like surfers who spend a lot of time in the sea, and go further out.”

Chumming, where shark tour operators use a mixture containing fish blood to attract sharks, has also often been proposed as a cause of attacks, although this is hotly contested. “It’s hard to prove that chumming causes more attacks,” says Cliff. “The practice has been going on in this country since 1991, and since then the increase in attacks has been slight.”

Could pollution increase shark attacks?
Southern African coastal waters don’t fall into one of the hundreds of recognised ‘dead zones’ – oxygen-poor areas of the ocean that result from nitrate pollution – which may force sharks to look for food in areas closer to popular beaches.

Most of the dead zones are situated in coastal areas near developed countries, from where the bulk of nitrates is entering the environment. That doesn’t mean, though, that nitrates from South Africa’s fertilisers aren’t having an impact on ocean life, but at this stage it can’t be said to be affecting numbers of shark attacks.

 - Olivia Rose-Innes, EnviroHealth editor, Health24, updated April 2010)

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