The first International Union for the Conservation of Nature (IUCN) red list of oceanic sharks names 64 species as endangered. Sharks are vulnerable because they take decades to mature and produce few young

Overfishing threatens to drive a third of the world's open-ocean shark species to extinction, say conservationists. Hammerheads, giant devil rays and porbeagle sharks are among 64 species on the first ever red list for oceanic sharks produced by the International Union for Conservation of Nature (IUCN).

Sharks are vulnerable because they can take decades to mature and they produce few young. The scalloped hammerhead shark, which has declined by 99% over the past 30 years in some parts of the world, is particularly vulnerable and has been given globally endangered status on the red list, which means it is nearing extinction. In the Gulf of Mexico, the oceanic whitetip shark has declined by a similar amount.

Scientists estimate that shark populations in the north-west Atlantic Ocean have declined by an average of 50% since the early 1970s.

Announcing the red list of open-ocean or "pelagic" sharks and rays today, scientists called on governments to set limits for catching the animals on the high seas and to enforce strict bans on "finning" – the practice of catching sharks, cutting off their fins and throwing the bodies back in the water.

"Despite mounting threats, sharks remain virtually unprotected on the high seas," said Sonja Fordham, deputy chair of the shark specialist group at the IUCN and policy director for the Shark Alliance. "The vulnerability and lengthy migrations of most open-ocean sharks call for coordinated, international conservation plans. Our report documents serious overfishing of these species in national and international waters, and demonstrates a clear need for immediate action on a global scale."

Pelagic sharks are usually caught on the high seas in tuna or swordfish fisheries. In 2007, 21 shark-fishing nations reported catching more than 10,000 tonnes of shark. The top five – Indonesia, India, Taiwan, Spain and Mexico – accounted for 42%.

At one time, sharks were considered worthless bycatch, but they are increasingly being fished on purpose to serve emerging markets for their meat and fins, which are used in soups and can fetch more than £100 per kilogram. In places such as China, shark-fin soup could once only be afforded by the elite, but the growing numbers of middle-class people in the country has driven up demand.

To satisfy the growing market, some fishermen have taken to finning sharks. There are bans on this practice in operation around the world, but Fordham said the coverage is patchy and, in any case, enforcing the bans is difficult due to a lack of policing on the high seas.

"The overarching problem for sharks is that, for a variety of reasons, they've been considered low priority and they're traditionally low value compared with something like the tuna," said Fordham. "Also public image feeds into that – I don't know if there are people clamouring for their conservation."

Most species of pelagic shark take many years to mature and have relatively few young when they do reproduce. The IUCN's report highlights a study by scientists in Canada which showed that the population of porbeagle sharks, classified as vulnerable in the red list, has been so affected by fishing that it will take at least 100 years to recover. Yet the government still allows the animal to be fished in its waters.

The global dusky shark popualtion, also classed as vulnerable by the IUCN, could take up to 400 years to recover because the animals are not sexually mature until around 20 years of age and usually raise only one offspring at a time.

Fordham said that because many of the sharks on the red list are at the top of the food chain, their extinction could also cause major local ecological problems. "We know that most of these species are top predators and we know that removing the top predators usually has negative consequences to the system as a whole."

In 2007, Julia Baum of the Scripps Institution of Oceanography in California, who is also a member of IUCN shark specialist group, published a study showing how a major decline in the numbers of predatory sharks in the north Atlantic after 2000 had allowed populations of cownose rays, which are their prey, to explode. The rays in turn decimated the populations of bay scallop off North Carolina. "There was a fishery for bay scallops in North Carolina that lasted over a century uninterrupted and it was closed down in 2004 because of cownose rays," she said last year.

Conserving threatened shark species might not be difficult. Last year, Peter Klimley of the University of California, Davis, found that scalloped hammerhead sharks migrate along fixed "superhighways" in the oceans, speeding between a series of "stepping stone" sites near coastal islands ranging from Mexico to Ecuador. Focusing marine reserves around these hotspots might be a cost-effective way to conserve the species.

The IUCN sharks red list is published a few days before Spain is due to host an international meeting of the managers of tuna fisheries, where many of the sharks are caught. Scientists are also meeting in Denmark this week to produce advice for authorities on how to manage populations of Atlantic porbeagle sharks. "The completion of this global assessment of pelagic sharks and rays will provide an important baseline for monitoring the status of these keystone species in our oceans," said Roger McManus, vice-president for marine programmes at Conservation International.

• This article was amended on Friday 26 June 2009. We referred to the the International Union for the Conservation of Nature (IUCN) as the World Conservation Union. It no longer uses this name. This has been corrected.