Sharks: should we fear them?Comment on this story
Cape Town - Selachophobia – English (noun), abnormal and persistent fear or dislike of sharks. Why do sharks, and particularly great white sharks, evoke such a visceral fear in so many people? Particularly when, with a global population approaching 7.1 billion people, on average just 12 people a year die from shark attacks involving all shark species?
And to put it into some more perspective, about two million people die annually from malaria after being bitten by mosquitoes, while there are about 100 000 snake-bite fatalities annually, says New Zealand-born, Mossel Bay-based shark researcher Ryan Johnson.
“So it’s a very, very complicated question,” he says.
Johnson’s love affair with these often unfairly maligned ocean giants started in 1998 when he spent a few months on Dyer Island, near Danger Point – the heart of local great white habitat.
His lecture “Sharks – more threatened than threatening”, at UCT’s Summer School this week, was one of a three-part series, Great White Sharks in Cape Town. In it, Johnson agreed there were still very strong differences of opinion about these creatures.
“But love or hate sharks, they are fascinating, and very topical,” he added.
Great white sharks are probably one of the most multi-faceted species on the planet, having survived in their current form for millions of years, he pointed out.
“They are an evolutionary success story probably unmatched on Earth. They are just so much more than the one-dimensional ‘man-eating’ predator you so often see portrayed in the media. It’s a unique and fascinating creature – and so much more than just a toothy grin.”
Johnson said research had revealed that the word “shark” evoked more fear in people than any other word or phrase, including “torture”, “terrorism”, “genocide” and “car crash”. Yet all shark species combined caused an average of just 12 fatalities a year.
And while human victims were occasionally consumed by these sharks, fatalities were usually the result of blood loss. Most incidents involved a “bite and release”, with a survival rate of 85 percent.
Johnson explained that he had been the lead scientist aboard the Ocearch expedition, tagging sharks in False Bay in April last year when bodyboarder David Lilienfeld was killed by a great white at Kogel Bay, on the eastern shores of the bay.
Despite being exonerated of any possible link to this tragic death, some people reacted irrationally, making wild accusations against the researchers.
“It’s the first time I’ve been called a murderer.
“That was the hardest two weeks of my life, although of course what I went through was incomparable to what the (Lilienfeld) family went through,” he recalled.
“Great whites certainly are their own worst enemies. They are always going to be scary, and they do attack every now and then, but this species does have a place in the ecology, and it’s important to find solutions that will allow humans and sharks to co-exist in the future.”
Johnson pointed out that despite being fully protected in South African waters since 1991 – this was the first country to introduce such a conservation measure – there had been no growth rate in the estimated local population of great whites, and there were no signs that it would increase in the future.
But an even greater cause for concern, he suggested, was the significant decline in the mean size of those sharks that had been caught.
“Which means fewer animals are reaching adulthood, and there’s a smaller breeding stock, which is not healthy. These animals don’t live in Utopia and they face a number of threats, particularly from incidental fishing when they are caught by mistake.”
From information in a number of data bases, in the process of being combined, and from a study at Mossel Bay that found the number of great whites there to be about 450, scientists estimated that the total great white population in local waters was probably smaller than 2 000. “That is very few sharks,” Johnson said.
He explained that females took 16 years to reach maturity – when they were at least 4.5m long – and had a litter of between eight and 12 pups only every two years. From the available data on sharks that had been caught, the population was currently biologically unviable. “It doesn’t bode well for the health of the population of great whites.”
It was understandable that not everyone understood why great whites had to be protected, or agreed with conservation measures, Johnson said.
But such measures were fully justified because these sharks were a “keystone species” vital to the functioning of the marine ecosystem, and reducing their numbers would have “massive” effects cascading all the way down through this ecosystem.
Such effects were not always easy to quantify, but there was a good example from the eastern US seaboard where a thriving, century-old clam and scallop fishery had been devastated because all the big sharks had been eliminated.
This had allowed an explosion of secondary predators – rays – that fed on the clams and scallops, but the numbers of which had been kept in check because they were the natural prey of the top predator sharks.
Locally, the ecological effects of shark fishing – including great whites historically, but now centred on the Sevengill Shark – were impossible to predict, Johnson said.
“But it’s guaranteed to have some marked effect, and I guess it’s our job not to let that happen.”
* On the web, http://www.ryan-johnson.org/