Environmentalists on Monday unveiled unprecedented footage of a legendary sea creature, the giant oarfish, as they stepped up a campaign against bottom trawling.

The origin of the myth of the sea serpent -- a snake deemed capable of capsizing vessels and swallowing crew -- the giant oarfish reaches a length of 11 metres (36 feet) and more than 250 kilos (550 pounds).

Eel-like in appearance, the creature (Regalecus glesne) is the world's longest bony fish.

It is only rarely seen by humans, and usually only as a bizarre, unwanted bycatch from commercial fishing.

At a press conference in Paris, ocean conservationists showed exclusive footage of the sinuous giant in its deep-sea environment as part of its effort to highlight dangers from trawling the sea bed.

"It's a key moment for the deep ocean," said Matthew Gianni of the Deep Sea Conservation Coalition, an umbrella of more than 70 associations.

Marine biologists say deep-sea bottom trawling, in which nets are scraped along the ocean floor, causes catastrophic damage to corals, sponges and micro-flora that are vital for the ecological web.

Places that were ploughed up decades ago have still to recover, said Claire Nouvian, head of a non-profit group called Bloom.

Bottom trawling also accidentally nets species such as the regalec which have no commercial value.

France and Spain, whose fishing industries wield political clout, are fighting attempts by the European Commission to outlaw the practice.

A key vote takes place in Brussels on October 3.

EU countries account for about 60 percent of global catch for deep-sea bottom trawling, the coalition said on its website, citing figures for 2001.