By Richard Black
Environment Correspondent, BBC News website
Conservation groups are calling for a UN moratorium on the fishing practice known as bottom trawling.
Ships trail heavy nets across the ocean floor, catching fish but destroying coral and other organisms.
Bottom trawling accounts for a tiny fraction of the global fish catch, which conservationists say is out of proportion to the damage it causes.
Fisheries negotiations begin Wednesday at the UN in New York, and will continue to the end of November.
"There are many countries now backing a full ban when the UN General Assembly meets," said Rémi Parmentier from the Deep Sea Conservation Coalition, an umbrella organisation including a number of conservation groups.
"We are pressing for a moratorium on high-seas bottom trawling because where the vulnerable areas are located is not really known," he told the BBC News website
High risk, low reward
With many continental fish stocks in steep decline, some fleets have adopted bottom trawling as a way to keep supplies flowing; even so, it accounts for less than 1% of the total global fish catch.
Powerful boats tow nets which extend to the sea floor; on the end of the net is a heavy roller or plough which keeps the net in contact with the bottom.
This ensures that any fish in the vicinity are caught, but so is everything else.
A report compiled last year for IUCN, the World Conservation Union, and other environmental groups concluded that bottom trawling is "...highly destructive to the biodiversity associated with seamounts and deep-sea coral ecosystems and... likely to pose significant risks to this biodiversity, including the risk of species extinction."
If these areas have to be fished, conservation biologists would prefer a move to longlines, perhaps tethered above the deep cold-water reefs and seamounts whose abundance and ecological importance has only been recognised in recent years.
Species living in the cold depths tend to live long lives and reproduce slowly. The orange roughy, a target of fishing fleets, can live for more than a century and takes decades to reach sexual maturity.
They are most plentiful on seamounts and in deep-water coral reefs.
But fishing here can cause substantial ecological damage. Last year, 1,100 scientists put their names to a petition arguing that the damage is too great, and supporting the demand for a moratorium.
This demand was submitted to UN delegations during negotiations preceding last November's General Assembly.
But deliberations resulted in a compromise pledge to "...consider on a case-by-case basis and on a scientific basis ...the interim prohibition of destructive fishing practices, including bottom trawling that has adverse impacts on vulnerable marine ecosystems, including seamounts, hydrothermal vents and cold water corals..."
The big year?
This year, conservation groups say they detect signs that some nations which have until now been strong supporters of bottom trawling may be changing their stance.
The most significant is Spain, whose fleets are responsible for approximately 40% of the global catch.
The Deep Sea Conservation Coalition has received documents indicating that the Spanish government now admits bottom trawling to be a destructive practice, and will in future commission scientific research to assess regions of ocean floor before allowing its fleet to fish there.
"This statement is indicative that they're on the defensive," said Rémi Parmentier, "and the argument they have been using - that environmentalists were making it all up - loses any credibility.
"In Spain, the anchovy fisheries off the northern coast have collapsed - not due to bottom trawling, but through the same pattern of looking only after short-term interests.
"They have learned that if they destroy natural resources, they will build their own tomb."
The New Zealand government recently announced that it "...would be prepared to support, in principle, the concept of an interim global moratorium... at a minimum, New Zealand would need to be confident of the commitment of key likeminded fishing nations to a moratorium before lending its support to the proposal."
For discussions on a moratorium to begin, conservation groups now need to persuade one national delegation to propose it.
Costa Rica has taken this role in the past, and conservationists believe they have almost identified this year's standard-bearer.