"We are advocating a moratorium on all bottom trawling on the high seas," she told a news conference.

"One 15 minute trawl can lay a deep seabed habitat to waste, destroying cold water corals which have taken millennia to grow," she added. "It is fisheries piracy."

The DSCC, grouping international environmental organizations including Greenpeace and the World Wide Fund for Nature (WWF), said the trawlers were hunting mainly for Orange Roughy fish which shoal around undersea mountains or so-called seamounts.

But such was the indiscriminate nature of their methods that 95 percent of the material caught by the steel nets dragged along the seabed at depths of up to 1.2 miles was simply thrown overboard again, dead, destroyed or dying.

"These trawls really do devastate the seabed, destroying everything in their paths," said marine biologist Alex Rogers from the British Antarctic Survey.

Seamounts, classified as geological outcrops rising at least 1,000 yards from the ocean bed, had been found to be teeming communities harboring possibly millions of species - many as yet undiscovered and most unique to their area.

The scientists said only about 11 nations including Russia, Japan, New Zealand, Iceland and Norway were the main culprits, using industrial methods to reap their marine harvest.

European boats - notably from Spain, Portugal and Denmark - accounted for 60 percent of the recorded catch.

But as the high seas fisheries were unregulated it was impossible to be sure of the full extent of the plunder.

Not only was vital biodiversity being squandered, they said, but there was neither an environmental nor an economic justification of the practice.

"They move in, destroy a seamount and move on. There is no way anyone can claim this is sustainable," said Alistair Graham, marine adviser to the WWF. "This is a luxury game, not a sustainability game."

The U.N., which has talked around the issue for the past three years, had to act now before it was too late.

"There are very few boats involved at the moment, but it is growing rapidly," he said. "There is a goldrush mentality. There are no rules in place - we need a moratorium to buy time."