Over-exploitation of traditional fish such as cod and hake has prompted fleets to trawl the high seas for deep-dwelling species such as orange roughy, alfonsino and roundnose grenadier, but they are harming biodiversity in vulnerable regions of the Pacific, Atlantic and Indian Oceans.

"There is an urgency, first of all, to deal with regulating those fisheries and secondly to get out there and look at those habitats before they are gone," said Dr Alex Rogers, of the Zoological Society of London and a co-author of the report.

"Fish hundreds of years old are being decimated as a result of this trawling," he told a news briefing.

The report will be presented at the United Nations, which is debating a plan to ban deep sea bottom-trawling in unregulated areas. It reveals new findings about the underwater mountains, some of which rise 1,000 metres (yards) from the sea floor, and the creatures that thrive on them.

The precise number of large seamounts worldwide is unknown. It is estimated to be around 100,000 but Rogers said scientific information exists on only about 40.

The report used coral records on seamounts and global data sets on environmental factors and computer modelling to plot the potential global distribution of stony corals on seamounts and areas particularly vulnerable to deep sea trawling.

It says more commercial fishing for alfonsino and orange roughy in the central-eastern Southern Indian Ocean, in the South Atlantic and in some regions of the southern-central Pacific Ocean are likely to have a negative impact on seamount ecosystems.

Matthew Gianni, a fisheries expert and author of a report on the impact of trawl fisheries and their impact, told the briefing that 11 countries are responsible for 95 percent of high seas bottom-trawling.

Spain, which has the largest fleet, had about 40 percent of the bottom trawl catch in 2001, followed by Russia with 14 percent, Portugal, Estonia and Norway with 7 percent each.