For 40 years, ever since Jaws set box-office records and struck terror into the hearts of a generation, there’s been a counter-movement to rehabilitate the reputation of sharks. Marine scientists were appalled by the film, and have spent nearly half a century telling us that these sinister creatures are just misunderstood. Very few sharks are dangerous, they say. Do not be afraid! But I’ve dived with hundreds of sharks, and I’m scared of them. Sharks are terrifying — that’s what makes them great.

I’ve been fascinated by sharks ever since watching Jaws as a teenager. I have more than 40 books about them on my shelves and I read any report of shark attacks I can find. Last weekend a teenage girl and a teenage boy both lost an arm in separate incidents on the same beach in North Carolina. In Réunion there have been seven fatal shark attacks in the past four years: in April, 13-year-old Elio Canestri was virtually bitten in half. I know a wildlife film-maker who almost lost an arm to a supposedly harmless grey reef shark, and a woman who was lucky to survive after a rapid attack from a 3ft-long blacktip.

When I go into the sharks’ environment I expect to have to watch them just as carefully as I would a lion if I were on safari. But it’s this very deadliness that makes sharks so appealing. Without a decent dose of fear, we would lose interest. Visit any of the websites urging us to protect sharks and you will soon be told that there is more chance of being killed by a bee than of being eaten by a shark. Indeed, shark conservationists frown at the idea of being ‘eaten’ at all. Statistics prove that more than half of all injuries to people are the result of ‘exploratory bites’, after which the shark swims off, having established that it doesn’t like the taste of human flesh.

I don’t quibble with all that. Just three, possibly four, species of shark account for more than 90 per cent of human deaths; the great whites, bull sharks and tiger sharks. Oceanic whitetips are the other bad boys, but unless you are a shipwreck survivor you’ll hardly have the chance to meet them. That leaves more than 400 species which are unlikely to bite, let alone kill. According to the International Shark Attack File in the USA, the chances of being bitten by a shark are about one in 400 million. In an average year, one or perhaps two people in the developed world are killed by sharks. Domestic dogs kill hundreds more. And it’s true that in the USA roughly one person a week dies from an insect sting. Golfers have a more realistic chance of being hit by lightning. (In Britain a similar argument has shown that whereas 29 people a year drown in the bath, only five people on average per year are killed by terrorists. But that doesn’t stop me worrying about terrorism.)

I’ve dived with sharks, big and small, all over the world. I admire them for their grace and power. Nothing swims as effortlessly or as gracefully. They can smell blood at concentrations as low as one part per million in the sea. They can detect the minutest electrical discharge given off by a fish in the dark, swim from Cape Town to Perth, and find their way back again to the same stretch of reef year after year. Great whites and several other species are now known to be partially warm-blooded, unlike almost all other fish. Mako sharks have been recorded achieving speeds of more than 40 miles an hour. They are nature’s finest killers. That makes them beautiful — and worth conserving.

The International Union for the Conservation of Nature says that a third of all oceanic shark species are at risk of extinction. Populations of oceanic whitetips have declined by over 90 per cent in the past thirty years. And between 70 and 100 million sharks are killed by man annually, many of them for use as ingredients in Chinese shark-fin soup. That’s in spite of countless conservation groups’ efforts to harness sympathy for sharks.

Perhaps the conservationists would do better if they realised that fear was their best weapon. I am not the only underwater naturalist for whom Jaws inspired a lifelong sense of awe. Losing our fear of sharks would be about the worst thing we could do for them.