Return of the great white killer

There was no warning, no trace of the menacing score that accompanied the mythic monster of Jaws. Teenager Nick Peterson could surely not have known what struck him as he stretched on his surfboard last week. The shark's first bite severed his torso, onlookers howled as the blue-green sea off Adelaide turned red with his blood.

Yet it was what happened during the next frenzied moments that has stunned the world's leading shark experts and sparked speculation that nature's sleekest predator, the great white shark, has never been more fearsome.

Scientists say that typically a great white shark spits out chunks of human flesh after the first bite. Yet just after 4pm last Thursday, 300 miles off the West Beach in Adelaide, the natural order was abandoned. Rather than leave Peterson half-dead in the waters, the creature stepped up its attack.

Peterson's body was savaged. Last night, despite exhaustive searches, no part of him had been recovered. Experts are struggling to explain why the 16ft creature targeted the powerful swimmer with such savagery. And attention has swung to a remarkably similar sequence of events that occurred a month ago, 7,000 miles away off Cape Town.

Those who watched Tyna Webb during her final morning swim off the beach near Fish Hoek recall a large dark form circling the 77-year-old. As with Peterson, the attack was unprovoked. Again, her body has never been found. Witnesses in a helicopter described the shape of a great white shark, bigger than the machine they peered from, swimming from the scene apparently with a body in its jaws.

Two attacks of such ferocity have never occurred so closely together and both events have raised questions about whether it is possible that after 400 million years the great shark has entered a new stage of development.

Alexia Morvan of the International Shark Attack File at the Florida Museum of Natural History, who is considered the world's most authoritative source of data, believes it is too early to tell. 'I don't know whether there is a change in behaviour, but we have never seen two such violent attacks in such a short period ever before. Normally we see a single bite, but these were more like a deliberate kill.'

Concerns that the world's most-feared creature has become even more terrifying were amplified by the fact that Peterson's death came just five days after a shark mauled 38-year-old Mark Thompson to death on the Great Barrier Reef. Thompson died before onlookers could pull him to safety, although, according to Morvan, the fact he was spearfishing means his death cannot be categorised as unprovoked.

Yet just why have the attacks become so ferocious? Among the theories expounded over the recent high casualty list is the fact that more people spend time in the ocean than ever before. 'There are more leisure users, more surfers, more swimmers, more guys out fishing than ever,' said Richard Pierce, chairman of the Plymouth-based Shark Trust.

Global warming too may play its part. The temperature of the sea is rising, species are being driven into colder waters and scientists are looking into whether the shifting food chain is confusing or agitating some of the most confident and lethal creatures of the sea.

Simon Greenstreet was in his element. As the sun sparkled off the sea close to Ullapool, on the west coast of Scotland, the marine biologist was enjoying a productive day's diving with his wife Wendy and two friends.

Then, at 2:30pm on 4 July last year, came the sight that no one present thought possible - a triangular fin slicing the water's surface. The shark kept approaching, sliding alongside their 19ft boat. From its size to its colour to its shape to the way it nudged up to their vessel, those on board were convinced of one thing - this was a great white shark in British waters.

That same day, 600 miles away, Richard Pierce was bobbing off the Cornish coast. The 55-year-old was hoping to encounter that dorsal fin so distinct to the millions who have seen Jaws . As chairman of the Shark Trust, Pierce had set sail from Padstow that morning determined to become the first man to photograph a great white in UK waters. Years of tracking the species across the world had convinced Pierce the predator had arrived in Britain.

The last confirmed sighting of a great white in European waters was in 1997 when a female was found in the Bay of Biscay, 250 miles from Cornwall. Tagging experiments show great whites can travel 7,000 miles in three months.'They are global nomads, travelling such a distance to Britain would be nothing,' said Pierce.

Despite this appetite for globe-trotting, the last fatal shark attack in Europe was 20 years ago. The most recent shark attack in Britain was in 1996 in the North Sea. However scientists now believe more are to come.

Climate change is already precipitating a dramatic change in the entire ecology of the sea. Sharks are thought to be migrating north due to rising water temperatures. Experts at the Shark Trust claim great whites can tolerate temperatures of 6C, warmer than some of the waters off the Cape in South Africa, one of the more noto rious cruising grounds of the great white.

The great white shark has become emblematic of mankind's obsession with monsters. Even now it is capable of stirring up a mythic fear. For, despite vast leaps of knowledge since Jaws was released 30 years ago, no one knows how big they can grow, how long they live or even how many are out there. Yet, although the deaths of Webb and Peterson have served to underline the shark's demonic status, conservationists last week were quick to point out that man rather than the shark is often to blame for the attacks.

But at a meeting last Friday the Australian government, police, fisheries and coast guard officials agreed that the creature that killed Peterson should be destroyed. Today the search will continue for that shark following two further sightings in the vicinity of the beach where the attack took place. It is a move that has infuriated Peterson's father Philip. 'Sharks are to be admired, appreciated and respected,' he said.

Marine conservationists were also quick to say that the numbers of shark attacks remain minuscule, with, for example, dogs biting thousands more people. During 2004, 51 unprovoked attacks by sharks, including seven deaths, have been recorded. Last year the figure was 55 with four fatalities. According to Australian researchers badly wired Christmas trees claim more victims each year.

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