Pictures of a massive dead Great White shark on the back of a bakkie are doing the rounds on email with the subject line saying "Caught at Monwabisi and Strandfontein Beach yesterday" - but experts have dismissed it as a hoax.

The grim pictures show the shark with a hook and trace still attached. Kalk Bay harbour master Pat Stacey says the pictures appear to have been taken in Australia.

He said it was virtually impossible for a shark that size to be caught and for it to be kept quiet. "Someone will always tell us and the trek fishermen would also report it."

Stacey believes it was someone simply trying to cause a sensation. Anyone who killed a Great White faced 10 years in prison or a R50 000 fine.

Earlier, a vigilante group threatened to bait Great Whites with chickens stuffed with broken glass and to shoot every shark in False Bay, after Tyna Webb, 77, was killed by a shark at Fish Hoek. But Mike Meyer of Marine and Coastal Management believes it was just hysteria.

He said at least three people had confirmed that the shark pictures had been taken years ago. "It's a hoax and just as well," he said. Meyer said Marine and Coastal Management had tried to track the origin of the email but it had been sent to so many people that it was difficult to find where it started.

He wished people would put the issue in perspective: "So few people are killed by sharks compared to hippos and other wild animals, yet there is so much hysteria around a shark attack."

And these weren't the first hoax pictures Meyer had seen.

"There is one that turns up every so often, of huge sharks near bathers off a beach in KwaZulu-Natal during a sardine run. But someone has just Photoshopped them in - we have the original picture in which there are no sharks."