Friday, October 28, 2005

Responsible for shark attack or not?

Accusations that the activities of shark boat operators led to the attack on Stiaan van Zyl at the weekend don't make sense, said Kim Maclean, a pioneer in the shark cage diving industry and acting chairperson of the Great White Protection Foundation.

There are also indications the shark involved in the attack wasn't even a Great White, she said. Maclean is one of eight shark cage-diving operators in the Gansbaai area and one of only 11 in the country.

She said a swimmer would probably have been able to spot a Great White in water that was only about 1.5m deep. The attack also didn't correspond to typical Great White behaviour. It is possible a smaller shark species could have been involved, like a ragged-tooth shark, which would be more likely to swim in the shallows.

Maclean said she wouldn't want to make a final decision until she'd seen the tooth marks on Van Zyl's leg but she agrees with experts such as Wilfred Chivell from Gansbaai that if it had been a Great White, Van Zyl would've lost his leg. She agrees with Chivell it was probably a curious experimental bite.

Regarding the allegations against cage-diving operators, Maclean said research has not been able to prove a link between attacks and activities of the shark boat operations.

Great White shark nomadic by nature

Those who want to blame these operators claim the practice of luring sharks with bait (so-called "chum", a mixture of blood and scraps) causes Great White sharks to associate humans with food.
Maclean said the latest research seems to show the Great White shark is nomadic by nature and remains in a certain location for four months at most before moving on.

"That isn't enough time to change established eating and hunting patons that have been entrenched through centuries," she said.

She referred to an article that appeared in Africa Geographic last month that discussed the preliminary findings of researchers Michael Scholl and Thomas P Peschak.

Her own observations over the past 14 years correspond to that of the researchers, Maclean said.

Female sharks do move closer to beach

Scholl and Peschak found, among other things that the current behavioural patterns of the Great Whites in the Gansbaai area have not changed from what they were many years ago.

Their observations showed sharks converge in large numbers on Dyer Island, south of Gansbaai, only at certain times of the year, probably to breed and give birth.

In summer, many of the female sharks do move closer to the beach, but these sharks seem not to be interested in food. When the bait of the boats end up among them, they ignore it.

The researchers ascribe this to a variety of possible causes. They speculate the appetites of the females might be reduced during this time of the year to prevent them from eating their newly born young.

Sharks at Dyer Island, on the other hand, are more lively and do react to bait from the boats, Scholl and Peschak said.


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