The Sea Shepherd Conservation Society's announcement came two days after the more mainstream environmental movement Greenpeace also said it was ending its pursuit of Japan's controversial annual whaling expedition.

Sea Shepherd said its ship, named after late Australian environmentalist Steve Irwin, would head back to Melbourne 'within a few days'.

'Our objective now is to keep the hunt from resuming before the end of January. Unfortunately our fuel reserves will not allow us to stay longer than that,' Sea Shepherd's founder, Paul Watson, said in a statement.

The Canadian campaigner appealed for assistance to fund fuel and repair work so the ship could quickly return to sea.

'We need to make every effort to keep the pressure on the Japanese whaling fleet, to keep them on the move and to keep them from killing whales. Given the fuel, we can keep up the pressure,' he said.

Japan halted its hunt after clashes in mid-January with activists on the Steve Irwin who hurled stink bombs at the whaling fleet.

Two Sea Shepherd activists, a Briton and an Australian, hopped onto a harpoon vessel in mid-January, setting off a two-day standoff that was resolved after Australia picked up the pair and handed them back to the Steve Irwin.

Japan, defying most Western nations, kills some 1,000 whales a year using a loophole in a 1986 global whaling moratorium that allows 'lethal research' on the giant mammals.

Japan makes no secret that the meat ends up on dinner plates and accuses Western countries of disrespecting its culture. Only Norway and Iceland defy the moratorium on commercial whaling outright.

Sea Shepherd, funded in part by celebrity supporters, has a longrunning feud with Greenpeace, which has also followed the Japanese whalers but says more militant tactics are counterproductive.

Australia's new left-leaning government has sent a customs boat to the Southern Ocean to document the whalers' activities to potentially pursue an international case against them. -- AFP