WHEN the film Jaws was released in 1975, sharks were in sharp decline off the US coastline. Thirty years later, conservation efforts have been so successful that it really is no longer safe to go back in the water.

This week three teenagers were mauled, one fatally, by bull sharks off Florida. Marine experts there are urging tourists to “wake up” to the dangers and to think of the Florida coast as a dangerous wilderness.

Fishermen, meanwhile, have told The Times that scientists have underestimated the shark population. The owner of one fishery said: “Sometimes it’s so thick out there with sharks, you could almost walk on them.”

A fact sheet for tourists, “Reducing the Risk of a Shark Encounter”, has been published for tourists by Visit Florida after the attacks this week.

Scientists have long argued that the rise in attacks since the early 1990s is because of the increase in the number of tourists in areas inhabited by instinctively territorial sharks.

But some now agree that the rising shark population is also likely to have had an effect. George Burgess, director of the International Shark Attack File, at the Florida Museum of Natural History, said:

“There are more sharks out there so, inevitably, there are going to be more attacks. But the huge number of tourists . . . has now also reached a critical mass. The opportunity for interacting with a shark is just much higher than it used to be. People need to start accepting the risks associated with going into what is a wilderness area. Sharks are owed their existence. We are going into their environment, not the other way round.”

Fears about dwindling shark numbers first prompted Florida’s federal government to impose fishing restrictions in 1993. Shark attacks off the coast of Florida have almost tripled since 1994, to 30 a year. Stocks of the aggressive blacktip and sandbar shark are thought to have been restored.

In 1995, the state banned commercial netting, creating a safe haven for sharks and a regular food supply as mullet stocks increased.

About half of the shark species that live off Florida have attacked bathers there. Spinner sharks, blacktips and hammerheads carry out most attacks, but the 8ft-long bull shark, responsible for the attacks this week, is the most likely to kill. It often inhabits shallow water.

Jamie Marie Daigle, 14, a holidaymaker from Louisiana, was swimming 250 yards from shore in the Gulf of Mexico when she was attacked. Her friends tried to rescue her, but the shark went after them, too.

Craig Hutto, 16, from Tennessee, was lucky to lose only a leg. Scientists said that he had provoked an attack by fishing while waist-deep in the sea. The live bait in his pocket is thought to have attracted a bull shark.

Armin Trojer, 19, an Austrian tourist, was bitten on the ankle while waist-deep in the sea. It was not known what sort of shark attacked him.

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