If you go for a dip off a Sussex beach in the summer the scariest thing you would expect to encounter is a spot of sewage or, if you're off Kemp Town, Brighton, a naturist.

The last thing you'd expect is a shark. But they're definitely out there - and we're not talking little tiddlers.

Last May a 6ft thresher shark was caught off Roedean.

In September 2000, another thresher shark, 12ft long, was caught in nets and landed at Shoreham. It's believed there is a small breeding ground for threshers off Seaford Head.

Tope, smooth-hound sharks and the giant basking shark are not uncommon visitors to the waters around Brighton.

Our changing climate has resulted in warmer sea water and sharks that usually cruise the Mediterranean are turning up in our waters, along with sun fish, trigger fish and barricuda.

Peter Jones, a curator at Brighton Sealife Centre, said: "There are more sitings of warmer water sharks than there used to be but as yet we have no exact figures."

But, however big the sharks might be, humans are unlikely to end up as their lunch.

Few species are known to attack man. There are only about 50 to 75 known shark attacks worldwide each year, just a handful of which are fatal.

More people are injured or killed by bee stings, snakes, crocodiles or tigers.

Despite the facts, our fear of sharks persists.

That fear also leads to a basic lack of respect for the shark. We have all seen photographs of a bloodied shark hauled up as some kind of trophy.

Imagine the reaction if that was a recently slaughtered tiger.

The reality is we are a much greater threat to sharks than they are to us.

Modern fishing techniques combined with a growing human population that derives about ten per cent of its protein from fish has meant shark populations everywhere have been decimated in the past 50 years.

According to the United Nations Food and Agricultural Organisation, more than 100 million sharks and shark-like fish are caught every year, many unintentionally.

But this is not the main reason for the depletion of the shark population.

"Finning is the major problem," said Peter. "It is very, very inhumane."

Finning is the practice of catching sharks, slicing off their fins and then throwing the animal back into the water, alive but incapable of swimming. It endures a long, lingering death.

The vast majority of shark fins are shipped to Asia where they are made into shark fin soup, considered a delicacy and status symbol. Once a luxury for the privileged few in southern China, economic prosperity has meant it is now mass produced and has become routine at weddings, banquets and business dinners No doubt if you were making a stand against eating shark, shark fin soup would be an easy dish to resist.

Consider, though, that rock salmon regularly turns up on fish and chip shop menus.

Actually a type of shark known as the spiny dogfish, it's population is in rapid decline.

Another big problem is there are no restrictions on how many sharks can be caught.

When Martin Ellis landed 65 porbeagle sharks off the Cornish coast during a single trip in December last year, he was not committing a crime. Nor did he have to take into account what size the sharks were.

Because sharks take many years to reach maturity - porbeagle sharks are actually still juveniles until they're more than 6ft in length - they are often killed before they have a chance to breed.

Sharks have an incredibly long gestation period, in some cases almost two years, which means most species only produce a few offspring in a lifetime.

This means shark populations are unable to rebound from overfishing.

As top predators, the possible extinction of sharks could have a major impact on marine ecosystems.

So should we be catching and eating shark at all?

Ali Hood, conservation officer at The Shark Trust, doesn't think so.

He said: "If a shark is caught up in nets intended for other fish, it is better it is eaten than go to waste.

"But there are some fisheries where shark make up the majority of the catch.

"What are needed are measures that ensure trawlers avoid areas heavily populated with sharks or known to be breeding grounds.

"Effective measures also need to be introduced to regulate shark and ray fisheries and ensure they are sustainable, which means quotas for how many sharks can be caught."

Meanwhile, the Sealife Centre is doing its best to educate people about sharks.

Peter said: "When people come in to see them, they get a different impression of sharks. They see they are not necessarily terrifying maneaters.

"Keeping sharks here means we can learn more about them and how best to conserve them.

"Some people have issues about keeping sharks in tanks but our sharks breed. If they are happy enough to do that, then they are happy in captivity."

For more information on shark conservation, go to www.sharktrust.co.uk