Call to great white sharks: come back!

According to a recent study, it suggests that there is evidence to support Karl Gegenbaur's theory that human limbs may have evolved from shark gills. File picture: Willem Law/Independent Media

According to a recent study, it suggests that there is evidence to support Karl Gegenbaur's theory that human limbs may have evolved from shark gills. File picture: Willem Law/Independent Media

Published Feb 5, 2015

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Cape Town - Great white sharks have been exceptionally scarce in False Bay this summer, with only 21 sightings in December and January compared to 50 to 60 sightings during these months in some years.

While surfers and swimmers may welcome the paucity of great whites in the bay, KwaZulu-Natal shark scientists doing research in False Bay are frustrated as they are unable to test their new electronic shark repellent cable off Glencairn Beach.

Paul von Blerck, a researcher from the KwaZulu-Natal Sharks Board who is heading the project and has been in Cape Town since October, said on Wednesday he was “at wits’ end” because of the lack of sharks.

“We’ve spent an arm and a leg on this equipment, and not a single white shark to date. No sharks means we can’t test the equipment. Even one animal would give us some direction,” Von Blerck said.

The equipment is a 100m electronic cable which emits a low-frequency, low-power electronic field. It is fixed to the sea-bed with vertical “risers” and the idea is that sharks, which are extremely sensitive, would move away from the area once they had detected the electronic field.

The sharks board wanted to test the cable to see whether it could be an effective alternative to the shark nets and drums used in KZN.

Glencairn was selected as the test spot because there was a good understanding of great white movements along the coast from Muizenberg to Glencairn, the water was fairly shallow and calm, and there were good vantage spots on the nearby Elsies Peak to observe shark behaviour when they encountered the cable.

A video camera has been installed on the peak. With a permit from the Department of Environmental Affairs, the cable off Glencairn was activated in November.

“Electrodes on the cable emit electronic pulses. We know it repels sharks in other situations, as it’s been tested on a smaller scale in Richards Bay, but we wanted to see if it worked in bigger situations. But we’ve had not a single white shark since we put the cable in the water.”

The camera on Elsies Peak rolls through the daylight hours. Once, when Shark Spotters reported a sighting of a great white, Von Blerck reviewed the footage but found it had been a copper shark.

“February is apparently the peak month for white sharks, so we’re still hoping, because mid-to-late March the shark season ends.”

Sarah Waries, project manager of Shark Spotters, said they did not have a data set covering a long enough time period to be able to say why there were so few sharks.

“It is probably natural fluctuations, but we can’t give a clear-cut reason. Shark movements depend on weather and water conditions, and the availability of prey. Perhaps the conditions in December and January were not conducive for prey, but we don’t know,” Waries said.

Cape Times

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