By Richard Black
Environment correspondent, BBC News website
More than half of the world's ocean-going sharks are at risk of extinction, a new analysis concludes.
Specialists with IUCN (formerly the World Conservation Union) found that 11 species are on the high-risk list, with five more showing signs of decline.
Sharks are particularly affected by over-fishing as they reproduce slowly.
The scientists are calling for global catch limits, an end to the practice of removing fins, and measures to minimise incidental catches (bycatch).
"There's this idea that because these are widely ranging species, they're more resilient to fishing pressure," said Sonja Fordham, deputy chair of the IUCN Shark Specialist Group (SSG) and policy director for the Shark Alliance conservation group.
"In fact they're becoming species of serious concern because there are no international catch limits for sharks. There are intense fisheries on the oceans, and they remain pretty much unprotected."
The SSG assessed data on the 21 species of sharks and their close cousins, the rays, that swim in upper portions of the open ocean where they are exposed to fishing fleets.
Of the 21, one - the giant devilray - is assessed as Endangered, and 10 are Vulnerable.
A further five are listed as Near Threatened, which means the signs of decline are not serious enough yet to merit a full listing.
The classifications are based on a range of criteria that look at past or forecast declines in population size. For example, a population shrinking by 50% in 10 years would usually qualify as Endangered.
Some of these species have been assessed before; but for others, including the three species of thresher sharks with their spectacularly long tails, the dangerlisting is new.
The main threat to sharks is fishing, both accidental and targeted.
The three thresher species are newly judged as Vulnerable to extinction
"They used to be taken as bycatch by boats targeting tuna and swordfish," said Ms Fordham. "But now as those species are declining we're seeing more fishermen targeting sharks.
"Porbeagle and shortfin mako are targeted for fins and meat; species like blue shark are likely to be finned, but particularly in Europe we're seeing more blue shark being landed."
Several of the bodies that regulate fisheries in international waters - the Regional Fisheries Management Organisations (RFMOs) - have set up measures to curb shark finning, but there are different standards in place, a situation that enables fishermen to work around the regulations.
As East Asian economies boom, conservation groups say the market for fins is increasing.
"Fishery managers and regional, national and international officials have a real obligation to improve this situation," commented Nicholas Dulvy from Simon Fraser University in Vancouver, the report's lead author.
"But it doesn't have to be like this. With sufficient public support and resulting political will, we can turn the tide."
The report was released at the Convention on Biological Diversity (CBD) meeting in Bonn, and will be published in the journal Aquatic Conservation: Marine and Freshwater Ecosystems.
The new risk assessments will be included in the IUCN Red List of Threatened Species when it is published later this year.