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Sometimes reaching over ten metres in length and up to seven tonnes in weight Basking sharks are the second-largest fish in the world, only the tropical whale shark is larger. To give you some idea of the enormity of these sharks, the biggest basking shark ever found was 13.72m long. This is roughly the same size and weight as a double decker bus.

Dive instructor Ollie Chambers, from Truro College Diving School between Porthcurno and Land's End during September 2007.

There were six Basking Sharks in the area at the time. At all times Ollie followed the shark code, which is set down by the Shark Trust. It states you should not approach the shark closer than 100m while in a boat, switch the boat engine to neutral, not touching the shark and keeping a distance of four metres while you are in the water with them.

This majestic creature is the largest wild animal regularly found in Britain's waters. Recent reports suggest that the basking shark, may be moving north - possibly as a result of climate change. Sightings of the sharks have increased by 65 per cent in Scottish waters over the last four years, and in south west England, traditionally the UK hotspot of basking shark activity, sightings have dropped by a massive 66 per cent.

Cornwall Wildlife Trust, together with other partners working towards conserving basking sharks, believe that many sharks die as a result of becoming entangled in fishing nets but because this often goes unseen and unrecorded it it difficult to prove this theory.

These huge filter feeders swim with their mouths wide open. They do have teeth, in fact they have hundreds of teeth, but they are tiny and of little use. They feed by sieving small animals such as plankton, baby fish and fish eggs from the sea through gill rakers which are made up of thousands of bristles about ten centimeters long. They can process over 6,000 litres an hour, expelling the water through the five pairs of gill slits.

Ruth Williams, Marine Conservation Officer for the Trust said, 鈥淏asking sharks appear off the coast of Cornwall in April with the highest numbers appearing in May and June. What determines these sharks behaviour is not fully understood."

"We know that they, like other sharks, use an acute sense of smell and detection of electrical activity to track their tiny prey. But many aspects of their life remain a mystery and they continue to be a subject for ongoing survey and research.鈥�

Ruth continued, "Divers also have the same responsibilities as other water users to respect these wonderful creatures so we urge you to abide by the Basking Shark Code of Conduct. Slow down or ideally cut your engines, don鈥檛 get too close, and don鈥檛 chase or harass them."

"Please remember that it is illegal to kill, injure or recklessly disturb basking sharks and other protected marine wildlife. Though these sharks do not normally present a threat to humans they can do a lot of unintentional damage with their tails so we advise people not to swim close to them if possible."