27 October 2005

South Africa: Researchers hope to lure great white sharks for tagging

Shark researchers will use a tuna tail as bait in shallow water in Fish Hoek in Cape Town to get close enough to a Great White shark to tag it.

No chumming will be done, and swimmers will be warned to get out of the water.

The decision comes after a meeting between the Shark Working Group and groups that use Fish Hoek bay, including the National Sea Rescue Institute, surf lifesavers, kayakers, swimmers and the ratepayers' association.

Shark group spokesperson Gregg Oelofse said: "There are social issues involved in attracting sharks so close to shore, which is why we held the meeting."

Last summer, shark watchers posted on the mountainside recorded Great Whites cruising through shallow water at Fish Hoek and Muizenberg when the sea was packed with bathers.

But the sharks were not acting aggressively and did not pay any attention to the bathers.

There is now scientific speculation that these two bays could be among historical breeding sites of this top ocean predator.

At Fish Hoek, huge Great Whites were recorded as swimming among the breakers less than 60m from the shore, while at the same time at Muizenberg, sharks were seen slightly further out - between 180m and 240m from the shore - in an area used by surfers and paddleskiers.

Sightings at Fish Hoek ended abruptly on December 26, and at Muizenberg on January 18.

Oelofse said they believed it was vital to tag one or two sharks to see if they were the ones that are regularly seen off Seal Island in winter.

University of Cape Town researcher Alison Kock has tagged several Seal Island sharks with acoustic transmitters and is tracking their movements with sea-bottom monitors at strategic places around False Bay. They receive signals when any tagged shark passes within about 300m.

But neither Kock nor researchers from the Marine and Coastal Management branch of the department of environmental affairs were 100 percent convinced the sharks found off Seal Island in winter were those spotted in sheltered bays in early summer, Oelofse said.

When the attempt was made to tag a shark, there would be tight safety precautions, and officials on Fish Hoek beach, the catwalk between the beach and Sunny Cove, and at Glencairn beach to warn people.

"If we're successful, we'll also go to the Muizenberg community to see whether they will also agree to having an 'inshore' shark tagged there, using bait to attract it."

The tagging would be weather-dependent and would be attempted during calm seas and a light north-westerly wind.

The researchers would attempt to put two tags on to the shark: an electronic acoustic tag that gives information to the bottom monitors, and a "pinger" tag that provides a VHF signal that can be used to track the animals directly.

"These pinger tags last for about three months, and the idea would be to monitor the shark for some 24 to 36 hours immediately after the tagging, and then during the course of the next few months, weather permitting," Oelofse said.

Source: www.iol.co.za


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