Fisheries experts and scientists have called for an end to subsidised deep-water trawling, which is stripping the oceans of slow-maturing "old growth" fish.

The American Association for the Advancement of Science annual meeting in San Francisco was told that government fuel subsidies enable "fishing fleets to operate like roving bandits, using state-of-the-art technologies to plunder the depths".

The conference heard that fishing was virtually unregulated in international waters beyond countries' exclusive economic zones, with no agencies to monitor and control catches. Deep-water trawlers drag 15-tonne nets along the seabed, typically 500m-1km below the surface. A side effect of bottom trawling is the destruction of deep-sea corals and sponge beds that have taken centuries or millennia to grow.

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The trawlers target fish such as orange roughy and grenadiers that grow ext-remely slowly in the cold ocean depths. In the Southern ocean, roughy reach sexual maturity at about 30 years old and live to about 150, said Selina Heppell of Oregon State University.

"When you buy orange roughy you are probably purchasing a fillet from a fish that is at least 50 years old," she added. "Most people don't think of the implications of that. Perhaps we need a guideline that says we shouldn't eat fish that are as old as our grandmothers."

Deep-water trawling is in-creasing because of over- fishing in coastal and shallow waters, said Robert Steneck of the University of Maine. "All fisheries are turning gradually into deep-sea fisheries because they have fished them out of the shallow waters," he said. "The solution is not going into the deep sea but better managing the shallow waters where fish live fast and die young but ecosystems have a greater potential for resilience."

A study by Rashid Sum-aila and Daniel Pauly of the University of British Columbia Fisheries Centre shows bottom trawling is only profitable be-cause of subsidies from some governments. Subsidies of more than $150m (£77m) a year are paid to deep-sea fisheries worldwide. Japan, Russia, South Korea and Spain are the biggest payers.

Most of these subsidies are for fuel. "Eliminating global subsidies would render these fleets economically unviable and would relieve tremendous pressure on overfishing and vulnerable deep-sea ecosystems," said Dr Sumaila.

There has been progress, however, with diplomacy to limit unsustainable fisheries. This month Japan, Korea, Russia and the US agreed to phase in a regional management regime for deep-sea fisheries in vulnerable areas of the north-west Pacific, and in December the United Nations General Assembly agreed a regime to regulate fisheries on the high seas.