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 World Conservation Union (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 northwest 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."