By BBC News Online's Jonathan Amos in Boston

Deep-sea trawlers are destroying populations of fish and other creatures in the ocean at an alarming rate, according to research presented at the American Association for the Advancement of Science annual meeting in Boston.

In the Southern Ocean lush forests of invertebrates have been literally stripped from the top of seamounts

Dr Callum Roberts

Fishermen are now using military sonar to hunt in the deep ocean, but the slow life cycles of the species that live hundreds of metres below the surface mean their populations will collapse if they are exposed to industrial-scale exploitation.

"In the deep sea, fishing gear is encountering species and habitats that are much less able to bounce back from the effects of fishing than those that live in the fast lane of the shallow seas," Dr Callum Roberts, from the University of York, UK, told the meeting.

"The pace of life in the deep sea is literally glacial. Species grow extremely slowly and they live to extraordinary ages, so, for example, the orange roughy can reach 150 years old and they don't reproduce until they are in their mid-20s to mid-30s."

Short-lived catches

Licensing fishing or introducing quota schemes to preserve stocks was unlikely to be effective, said Dr Roberts. Marine reserves, he believes, are the only answer. The problem is that deep-sea fisheries are in international waters and getting many countries to agree to a proposal that would close off thousands of square kilometres of ocean to trawlers will be extremely difficult.

"What is more, the move to deep-water fishing is being encouraged by governments who are offering subsidies to alleviate the hardship that has been brought on by the collapse of shallow-water fish stocks," Dr Roberts said.

"There is a worldwide scramble to exploit deep-sea fish. Forty percent of the world's trawling grounds are now waters that are deeper than the edge of the continental shelves."

The early rewards from deep-sea fishing can be extremely high. The orange roughy fisheries that took off in the 1980s around seamounts in the waters off New Zealand and Australia were said to be producing catches of 60 tonnes from a 20 minute trawl.

'Lush forests'

"But the decline came very swiftly and today there is less than 20% of the roughy there were 10 or 15 years ago," Dr Roberts said.

The impact of fishing in the deep sea goes far beyond just removing the fish. Fisheries are concentrated into places that have the greatest biological significance; places like seamounts and canyon walls where materials that are wafted in on currents support rich communities of species - corals, sponges, seafans and hydroids.

Deep-sea fishing is said to be inflicting terrible collateral damage on these species as trawl meshes plough through the water.

"Off the East Coast of North America bizarre and beautiful fields of glass sponges have been trawled to oblivion. In the Southern Ocean, 'lush forests' of invertebrates have been literally stripped from the top of seamounts by trawlers targeting orange roughy."