By Jonathan Fildes
Science and technology reporter, BBC News, San Francisco
Fuel subsidies that allow fishing fleets to "plunder" the deep seas should be scrapped, claim a group of leading international scientists.
Slow-growing coral species are at risk from trawling
They said more than $150m (£80m) was paid to trawler fleets, promoting overfishing of unviable resources.
In particular danger were slow-growing deep-sea fish and coral species caught by bottom trawling, they argued.
2006 UN talks failed to implement a ban on the method, which uses heavy nets and crushing rollers on the sea floor.
"Eliminating global subsidies would render these fleets economically unviable and would relieve tremendous pressure on overfishing and vulnerable deep-sea ecosystems," said Dr Rashid Sumaila, of the University of British Columbia.
Eleven nations have bottom-trawling fleets, with Spain's being the biggest.
Researchers at the University of British Columbia estimate that without subsidies, these fleets would operate at a loss of $50m (£27m) annually.
Most of the subsidies were for fuel, the marine researchers said, which allows the trawlers to travel far out to sea and drag the heavy nets needed for bottom-trawling.
"There is surely a better way for governments to spend money than by paying subsidies to a fleet that burns 1.1 billion litres of fuel annually to maintain paltry catches of old-growth fish," said Dr Daniel Pauly, one of the researchers who has looked at the issue.
Japan, South Korea, Russia, Australia and France are amongst the other countries that subside their trawlers.
Continuing payments to these fleets would inevitably lead to depleted fisheries, said Dr Pauly.
"You get a signal from the stock - I am old, I am rare and I am depleted," he said.
"Subsidies allow you to overlook that signal and keep fishing to the end."
Deep-sea species that are currently caught by deep-sea trawling methods include orange roughy, previously known as slimeheads, and Patagonian toothfish, better known as Chilean sea bass.
The fish were renamed to be more palatable to consumers.
Cold-water species like the orange roughy are particularly at risk because they lead such long lives.
"This is a species that grows so slowly that it might not reach sexual maturity until it is 34 years old and they live to be 150 years old," said Dr Selina Heppell, from Oregon State University.
"There is a strong correlation between living a long time and not reproducing very quickly so they are very easy to over exploit."
The fish also tend to cluster around seamounts and cold-water coral reefs.
Because deep-sea fishing methods are so indiscriminate these ecosystems can easily be destroyed.
"The corals like the fishes are extremely slow growing; they're also extremely long lived," said Dr Murray Roberts of the Scottish Association for Marine Science.
Species can live for up to 2,000 years, making them the longest-lived organisms in the sea.
"These animals can live for hundreds of years but they can be removed in one sweep," he said.
They are also important he said because the corals were an archive of past climates, locking in the chemical signatures of past sea water.
"We not only run the risk of losing a structure that supports fish but also a climate archive that we have only just begun to unravel," said Dr Roberts.
Last year, conservation groups and governments from countries such as the Netherlands and Norway argued for a ban on bottom-trawling at the United Nations.
But the talks ended with only an agreement for some precautionary measures to ensure that trawlers do not cause significant damage to marine ecosystems.
The compromise declared areas where deep-sea corals and other vulnerable species occur closed to bottom-trawling, unless fishing nations can prove their activities will do no harm.
And on 2 February this year, Japan, Korea, Russia and the US agreed to phase in a management plan for deep-sea fisheries around seamounts in the Northwest Pacific.
But even with these agreements, the scientists, assembled in San Francisco for the American Association for the Advancement of Science (AAAS) annual meeting, believe subsides need to be scrapped.
"From an ecological perspective, we cannot afford to destroy the deep sea," said Dr Sumaila.
"From an economic perspective, deep-sea fisheries cannot occur without government subsidies.
"The bottom line is that current deep fisheries are not sustainable."