21 November 2005

South Africa: Cape warned of increased shark activity

The great White shark tagged off Bailey's Cottage between St James and Muizenberg on Saturday, spent much of Sunday morning cruising slowly in circles off Muizenberg beach.

But at other times during the 24-hour period after its tagging, the 4.3-metre predator moved quite quickly several times between Bailey's Cottage and Sunrise Beach, researchers reported.

And at one point on Saturday night it headed out in the direction of Seal Island, but did not go all the way there.

The Shark Working Group, the umbrella body which is helping to coordinate research into the apex predators, has appealed to False Bay bathers to be extra vigilant and cautious as there appear to be a higher number of sharks in the area than usual.

Mike Meyer and Deon Kotze of the Marine and Coastal Management branch of the Department of Environmental Affairs succeeding in placing the acoustic tag on the shark on Saturday afternoon.

But "it appears to have a fault and it doesn't have the strength it should have," said Meyer.

"We tested another tag and that one worked perfectly, so we're thinking of putting another tag in (another shark) if we can. But at least we know a little bit about this one. It spent a long time just tracking in circles, which was quite surprising, but it moved quite fast otherwise."

The batteries in the acoustic tag should last for six months.

The department's research vessel Sardinops is also servicing and redeploying the shark listening stations in the bay, part of a separate but related study on Great Whites in False Bay by University of Cape Town scientist Alison Kock who earlier this year tagged more than 20 off Seal Island. Signals from the tags and data such as depth and sea temperature are recorded by the listening stations when the tagged Seal Island sharks swim within a couple of hundred metres of them.

Saturday's tagging, done in collaboration with the City of Cape Town under the banner of the Shark Working Group, is part of a larger study on the abundance, behaviour and distribution of white sharks.

"The main objectives of this study are to investigate if white sharks are permanent or seasonal residents in False Bay, if there are any preferred areas where they occur, if they form social groups, if they prey in the bay and if they do, where and on what," said Environmental Affairs spokeswoman Carol Moses.

"It will further explore if there are any times of the day that the sharks prefer to be inshore and the importance of Seal Island to the white sharks, if there are any possible stimuli that increase shark aggression that could lead to an attack on humans, the abundance of sharks, if there are seasonal trends in the number of sharks in the bay, and general behaviour of white sharks."

A genetic study is also under way with the University of Aberdeen in Scotland to determine if there is only a single population of white sharks in the southern hemisphere.

The larger study has indicated that the "South African" white shark moves widely - they tracked one, named Nicole, from Gansbaai to Australia and back - and is under threat on the high seas and in countries which do not protect them.

Source: www.iol.co.za


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