Sharks have been "much maligned" and should be protected rather than feared, according to a study of the decline in shark numbers in the Mediterranean.

Numbers of some shark species have fallen by 97 percent over the last two centuries because of overfishing, putting the sea's ecological balance at risk, says a report by the Lenfest Ocean Program in Washington.

The report, released in Rome today, used archive accounts of sightings, fishermen's logs, records of shark landings and museum specimens to estimate the number and size of the Mediterranean sharks over the last 200 years.

"Some shark species face extinction," Francesco Ferretti, the main author of the report, told The Times. He predicted that this would have a "huge impact on the ecosystem" because large predatory sharks were "at the top of the food chain", and their failure to consume smaller fish as prey was upsetting the ecological balance.

Mr Ferretti, a researcher at the Biology Department of Dalhousie University in Nova Scotia, said that Steven Spielberg's 1975 film Jaws had given a misleading impression of sharks. "Spielberg has a lot to answer for," he said. "In reality you have about as much chance of being eaten by a shark as you have of winning the lottery twice".

He said that he found the shark portrayed in the film funny rather than frightening. "It acts like a revenge-driven machine. If we ever find such a shark it would be of great interest to science". He said that in reality the shark population was "very vulnerable" because it produced few young sharks, which took a long time to mature. The mean size of sharks caught in the Mediterranean was "among the lowest in the world".

Five of the twenty big shark species in the Mediterranean - the hammerhead shark, thresher shark, blue shark and two species of mackerel shark - had declined by 97 percent on average, the report said. The evidence was that the Mediterranean had "lost much of its predator diversity due to prolonged and intense human exploitation".

Almost all of the large sharks had decreased in abundance because of "unintended capture in open ocean fisheries" as well as "targeted shark fishing and human population pressure in coastal areas".

A report last month (May) by the International Union for Conservation of Nature found that eleven species of shark worldwide face extinction because of overfishing. This was partly due to demand for shark fin soup in countries such as Indonesia and Spain.

Mr Ferretti said that sharks had been fished in the Mediterranean since Roman times, but that modern fishing methods were placing their survival at risk. Sharks were often caught as "by-catches" in fishing gear intended to snare tuna and swordfish.

The Lenfest study, published in the journal Conservation Biology, said there were 47 species of shark in the Mediterranean, of which 20 were considered "top predators". The hammerhead population is already almost extinct in the Mediterranean, where it has been rarely sighted for the past twenty years. A rise in jellyfish numbers and algae concentrations in the Mediterranean may be partly due to changes in the ecological balance because of falling numbers of predators, the report said.

Margaret Bowman, director of the Lenfest Ocean Program said: "This study makes an important contribution to our understanding of how multiple pressures are threatening sharks. We understand too little about the consequences of losing top predators to take shark declines so lightly." She said ecologists were campaigning for the European Union to impose catch limits for commercially-fished shark species in the Mediterranean.

Shark Facts

Hammerhead sharks have declined the fastest, with no recorded sightings in the Mediterranean since 1995

Hammerheads are estimated to have declined 99.99%

Blue sharks have declined by 96.53% in abundance and by by 99.83% in biomass in the last 50 years, with the steepest decline in the waters around Spain

The mackerel shark has declined by more than 99.99% in both abundance and biomass in the last over the last 100 years.

The thresher shark is the only species detected in coastal waters in recent times

Threshers have nonetheless declined by more than 99.99% over the last 100 years.

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