The following correction was printed in the Guardian's Corrections and clarifications column, Wednesday January 04 2006

In the report below, we wrongly suggested that the two environmental organisations concerned - Greenpeace and the Sea Shepherd Conservation Society - had accused each other of endangering lives by trying to ram one another's vessels. In fact, it was the Japanese factory ship and the Sea Shepherd vessel that accused each other of endangering lives, and not Greenpeace and Sea Shepherd.

A battle for what is being called "the high moral wave" was last night being fought off the wild coast of Antarctica as the world's two leading international marine protection groups fought each other over which would stop the Japanese whaling fleet.

With an international crew of volunteers, a helicopter and a deep warchest, Greenpeace International has sent two boats, the Arctic Sunrise and the faster Esperanza, to the Southern Ocean to stop the Japanese whaling fleet as it tries to catch 900 minke, blue and other whales for "scientific research".

Last night the group, which located and gave chase to the Japanese fleet before Christmas, claimed to have the whalers on the run in mountainous seas peppered with icebergs. "The fleet seems to be running in circles, stopping and going in different directions. It's the sixth day in a row that we have seen no whales transferred to the factory ship. It's unlikely that whaling is being undertaken," said a spokesman.

The animal rights protector Captain Paul Watson, who co-founded Greenpeace in the 1970s and later set up the more radical Sea Shepherd Conservation Society, was also in pursuit of the fleet yesterday in his ship, the Farley Mowat. Capt Watson, who accuses Greenpeace of being "the Avon ladies of the environment" and of being more interested in publicity than in enforcing international law, intercepted the Nisshin Maru factory ship on Christmas Day. Each environmental group now accuses the other of endangering lives by trying to ram its vessels.

Sea Shepherd had requested the presence of the Australian navy to monitor events in the Southern Ocean, but Australia's environment minister, Ian Campbell, said that Sea Shepherd's threats to attack the fleet "risk setting back the cause of whale conservation many years".

Capt Watson said yesterday: "Stop threatening us, Mr Campbell, and charge us if you believe we are acting unlawfully. Stop posing for the Japanese [who] are in blatant violation of international conservation laws."

Despite a short truce at Christmas in which the captains swapped greetings, Capt Watson and Greenpeace were at daggers drawn again yesterday with Sea Shepherd accusing the larger group of refusing to say where the Japanese fleet was.

"Greenpeace has misled Sea Shepherd and betrayed us. The Japanese fleet does not give a damn about protests. [Greenpeace] just take pictures and hang banners. We are down here to enforce international conservation law and to stop the illegal whaling operations."

Greenpeace retorted: "Greenpeace distance themselves from Sea Shepherd because of their inability to commit to non-violent tactics. But we'll do what we can to put bodies between harpoons and whales and protect the whales non-violently," said its spokesman Danny Kennedy. Capt Watson yesterday warned Greenpeace that Japan had dispatched a warship to the Southern Ocean to protect its whaling fleet and arrest the conservationists for piracy. This could not be confirmed.

Last night, the three conservation ships were reportedly trying to spot the Japanese harpoon vessels. "They are sweeping along the [Antarctic] coast corridor with radar and helicopter reconnaissance flights with the objective of ferreting out the positions of the illegal harpoon vessels," said a spokesman for Greenpeace.

Backstory

The bad blood between Greenpeace and Sea Shepherd goes back to 1979, when Captain Paul Watson, membership number 008, left the Greenpeace Foundation he helped set up in Canada in 1972. In 1978, he formed the Sea Shepherd society. While Greenpeace adopted an ethic of non-violence, Capt Watson, 55, believes in confrontation and has been accused of piracy and terrorism.