How not to get attacked by a shark
SCIENCE & TECH / 31 Jan '13By: John Yeld
Cape Town - The science underpinning an understanding of shark attacks is still not very robust, but if you really want to minimise the chance of being bitten by a great white while swimming in Cape Town, don’t venture behind the line of breaking waves at Strandfontein.
And if the water temperature in False Bay is warm and the moon is new, then it’s even more important not to go into the water.
A great white breaches off Seal Island. Picture Brenton Geac. Credit: INDEPENDENT NEWSPAPERS
That’s the word from shark researcher and Great White specialist Alison Kock, who has been studying these creatures since 2003.
Kock, currently completing her PhD at UCT and who is research manager of the city’s Shark Spotters programme, was talking on Science with Teeth as part of a three-lecture series Living with Great Whites in Cape Town that she convened for UCT’s Summer School this week.
She pointed out that the number of shark attacks was so low that it was impossible to find any statistically valid trends that could be usefully applied.
“We’re really grasping at straws to figure out why. Because attacks are so rare, we need to look at how sharks behave in their natural environment and then try to infer why they occasionally bite people.”
She confirmed that there was an increasing trend in shark attacks but said this was not unique to Cape Town or South Africa, and that the same trend had been found in California, Florida and Australia.
The only strong correlation was the rapid human population growth in all these areas which meant there were more people in the sea and for much longer periods – like surfers, who also spent much of their time behind the back line of waves.
Between 1960 and 2012, there were 29 shark “incidents” in Cape Town waters – these included bites on surfskis – of which six had been fatal. This equated to 0.55 attacks a year, with 0.11 annual fatalities during this period, Kock said.
There was a lot of generalised information about attacks but all shark species had been lumped together in this and the science was not strong. However, the Shark Spotters programme was producing incredibly valuable data – including that more than 70 percent of the close to 1 500 sharks in its nine years of operation had been recorded behind the back line of breakers.
Strandfontein was just 6km from Seal Island, where both male and female Great Whites congregated during the autumn and winter, and they had found that the females moved inshore in spring and summer. “Don’t go swimming at Strandfontein behind the breakers.”
Kock revealed that a student had found a “really strong correlation” between the presence of sharks and water temperature, with an eight times greater chance of sighting a shark at Muizenberg if the seawater was 180C as opposed to 140C and a five times greater chance at Fish Hoek – “That’s a really strong pattern”.
There was also a strong correlation with the lunar phase, with more sightings at new moon – “We think both the (water) temperature and the lunar phase has to do with prey availability,” Kock said.
She confirmed that there’d been an increased number of shark sightings at Muizenberg beach over the past three years and at Fish Hoek over the past two years, “but we can’t tell whether these are the same sharks being seen more often or whether there are more sharks”.
Every year the data collected was different, and long-term monitoring might provide a scientifically-based index, Kock said. Cape Argus