The shark, cetorhinus maximus, is Cornwall's equivalent of the African rhino but far more mysterious. Weighing up to five tons, the creatures can be seen hurtling six feet above the sea, performing majestic half- somersaults.
But this magnificent sight is becoming more rare. The number of sightings decreased by 85 per cent between 1989 and 1996.
So little is known about the shark, and so great is the concern for its fate, that the Wildlife Trusts and the Worldwide Fund for Nature have set up a group, called Seaquest, to monitor its numbers over the next three years.
"Killing the basking shark for its fins is as crass as killing tigers and rhinos for aphrodisiacs and medicines," said Colin Speedie, a marine naturalist and project director of Seaquest.
The basking shark is particularly vulnerable to hunting because it reproduces infrequently and the young are slow to mature. "They can't reproduce themselves out of trouble," said Mr Speedie. "If you start killing them their numbers diminish catastrophically."
The shark appears off the western coast of Britain during the summer, presumably on a migratory surge between Portugal and Iceland. Previous attempts to track them have failed because, it is thought, they hibernate in deep canyons at the edge of the continental shelf. There are believed to be other pods of basking sharks dispersed across the world's temperate waters including the north Pacific, South America as far north as Ecuador and the southern coasts of Australia and New Zealand.
The sharks were once caught mainly to provide liver oil, or cosmetics and specialist aviation oils. Until a few years ago there was only one Scottish fisherman with a licence to harpoon basking sharks. Now the threat comes from rising demand for their enormous dorsal fins for use in sharks fin soup, a Chinese delicacy.
It is a quick, easy and financially rewarding business. A basking shark can be harpooned, stripped of its fins and the carcass dumped overboard within 10 minutes.
Environmentalists are pinning their hopes on securing a Convention on the International Trade in Endangered Species (Cites) agreement for the shark, which would cut back the numbers culled.
MONSTERS THAT GATHER OFF BRITAIN'S HOLIDAY COASTS, BUT ARE A DANGER TO NO ONE
n The basking shark is the second largest fish in the world (after the whale shark) and the largest in British waters.
n Maximum recorded length: 10 metres.
n Maximum weight five tons.
n The young measure up to two metres at birth but are rarely seen until they reach more than three metres.
n They are bluish grey with upper surfaces in greyish brown or black.
n Harmless vegetarians, they filter 9,000 litres of water an hour for plankton.
n Found off the western and south-western coasts of Britain in summer, their winter waters are not known.
n In good weather they "bask" on the surface exposing both the dorsal and upper lobe of the tail fin, and sometimes the snout.
n Occasionally found alone, but usually in small groups, they have been sighted in shoals of 50 to 100. A record 500 were sighted off The Lizard in Cornwall last Spring.
n Hunters target them for their fins and large livers, which may amount to up to 25 per cent of their body weight.
n Females are thought to reach sexual maturity at around 20 years. They probably live as long as 50 years.
n In Britain, basking sharks pair in early summer. The length of the pregnancy is unknown, but it may last from one to three years.