Tuesday, November 07, 2006

Great White shark is being monitored

Sharks in Mexico are far larger than the sharks that have been scaring local beach-goers, according to local shark catcher and researcher Stephan Swanson. Along with a team of Mexican scientists and documentary film-makers from National Geographic, Swanson travelled to Guadalupe Island off Mexico's coast in October, where he became the first person to successfully catch and fit a five-metre Great White shark with a satellite transmitter. Swanson, from Lansdowne, is a highly experienced researcher and fisherman who worked for Marine and Coastal Management for 19 years. He left in 2005 to start his own business.

'They were huge and looked like mini submarines when passing my vessel'The 1.2 ton female Great White, named Claudia, was released unharmed into the Pacific Ocean after biological data was recorded. The shark is being monitored daily. The project aimed to monitor shark movement patterns to understand their migratory behaviour and how they interact with the surrounding eco-system."In South Africa, I had only ever seen two sharks over five metres in length," said Swanson.

"In Guadalupe, they were all between five and six-and-a-half metres in length. They were huge and looked like mini submarines when passing my vessel."The shark catching technique involved landing the shark on a custom-built cradle, where a satellite transmitter was fitted to its dorsal fin. A one-hour documentary on the expedition, Unlimited Shark, will be screened on National Geographic early in 2007.

The team's observations were of huge interest to local scientists as very few sexually mature females more than 4.5m long have been observed, leading to speculation that this segment of the population remains rare.

'There was a lot of adrenaline rushing through my body'Pretoria University PhD student Ryan Johnson, who is based in Cape Town to study Great Whites, said: "There was always a nagging thought in our minds that we were simply not seeing the really large sharks because they did not respond to chum. "It's interesting to know that at Guadalupe, six-metre Great Whites are routinely observed from boats. It raises the question: where are ours?"

After two failed attempts at catching the shark on the third day at sea off Guadalupe, a slight modification to the equipment ensured the team's success the following day."At first, the power and mass of the shark proved to be too much for our hooks, which straightened after hook-up and allowed the shark to escape," recalled Swanson. "But once I caught the shark, there was a lot of adrenaline rushing through my body." Once the shark had been hooked, the only noticeable difference to his South African experiences was the added stamina and mass of the shark.

"The only hurdle was fitting the five-metre shark into a cradle that was designed to hold sharks only up to four metres long," he said. Claudia was injected with vitamins and antibiotics by a qualified vet to aid her recovery from the ordeal and she was closely monitored while on the cradle, he said.The team's only disappointment was not being able to fit any larger sharks on the cradle and thus only catching Claudia.

Swanson said Guadalupe had a well-developed shark cage diving industry and found that there were many differences between the operations at Guadalupe and South Africa. He said that no regulations, permits or codes of conduct existed to govern cage diving operations, such as those in South Africa. Another major difference was that all the companies operating around the island were American and that the industry offered little economic or educational benefits for local Mexicans.

Over the days following the capture, transmissions showed that Claudia had been swimming near the island.Over the next few months, researchers will be able to follow her movements from their laboratories."Who knows, maybe Claudia will emulate the migratory feats of 'Nicole', the famous South African shark who stunned scientists by swimming from South Africa to Australia and back, the longest recorded migration of any shark," said Swanson.


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