The whaling fleet, outmatched by Sea Shepherd activists, turned north yesterday as Japan's Fisheries Minister, Michihiko Kano, announced its withdrawal.

He said Japan was calling the ships home ''to ensure the safety of the whaling crew amid the continuing harassment by the anti-whaling group Sea Shepherd''.

''Even now the mother ship is being chased, and it is difficult to ensure the safety of the crew members,'' he said.

The group's leader, Paul Watson, declared it VSO Day - Victory in the Southern Ocean Day - for whales.

It is the biggest setback for whaling in the Antarctic at least since the region was declared an International Whaling Commission sanctuary in 1994.

Japan rejected the sanctuary declaration, and kept on hunting using the commission's scientific research loophole, which it first employed after a global moratorium on commercial whaling was declared in 1986.

Activists from Greenpeace and Sea Shepherd tried for two decades to intervene against the hunt, but only this season did the latter's campaign strength finally outweigh the whalers.

Within hours of reaching the Antarctic this year, the four-ship whaling fleet came under sustained pressure from Sea Shepherd. Two of its harpoon ships were preoccupied for weeks trailing the activists' ships to ensure the factory ship Nisshin Maru stayed clear, the whalers' refuelling was delayed, and one harpoon ship was temporarily disabled by fouling ropes.

Mr Watson estimated that as few as 30 to 50 whales were taken by the Japanese fleet, out of a self-awarded quota of up to 985.

The last is believed to have been harpooned on February 9, when activists on the Australian-flagged Gojira caught the Nisshin Maru in the Ross Sea with blood pouring from its scuppers.

Since then Sea Shepherd's long-range ship, Bob Barker, has pursued Nisshin Maru far out of its whaling grounds.

''We had them in a position where they just could not kill whales,'' Mr Watson said. ''After seven years of coming down here, it's really gratifying to be able to go home for the season knowing that we have stopped the hunt. The next thing is to shut them down forever.''

The Prime Minister, Julia Gillard, said Australia would keep pursuing international legal action against Japanese whaling.

''There are the whaling seasons for the future, and from the point of view of the federal government we are very passionate about our commitment to end whaling,'' Ms Gillard said.

The detailed Australian case against Japan is due to be laid before the International Court of Justice in May.

Close observers of Japan believe the decision marks a fundamental shift in control, away from the Fisheries Agency of Japan, which was recently disgraced over a whale meat black market exposed by Greenpeace.

''We're hopeful that this signals a dramatic change of policy,'' said Patrick Ramage, global whales campaign manager for the International Fund for Animal Welfare in the US.

''It provides an opening for senior officials in the government at a much higher level than the Fisheries Agency to recognise that this is an uneconomic relic industry from last century.''