Japan has temporarily suspended its annual whale hunt in the Antarctic after anti-whaling activists obstructed its fleet's mother ship.
Officials in Tokyo have conceded that this year's mission, which had again been the target of international criticism, had not gone as well as hoped and the fleet may be called home early, according to reports.
Tatsuya Nakaoku, a fisheries agency official, said the decision was taken after the mother ship, the Nisshin Maru, was "harassed" by members of the marine conservation group Sea Shepherd.
"Putting a priority on safety, the fleet has halted scientific whaling for now," he said. "We are currently considering what to do next."
Reports said the government was considering halting the expedition entirely well before its scheduled end in mid-March.
Sea Shepherd described this year's campaign as its most successful yet. "I see victory on the horizon," a spokesman for the group, Peter Hammarstedt, told ABC News in Australia.
"I think certainly our actions down there have contributed to them possibly calling off their season early."
The Japanese fleet is thought to have killed between 30 and 100 whales – a fraction of its quota – since it arrived in Antarctic whaling grounds late last year.
The Sea Shepherd's vessel, the Bob Barker, located the fleet as soon as it arrived and has been pursuing the Nisshin Maru as it heads towards the Antarctic peninsula below South America. The harpoon ships are unable to kill whales unless the mother ship is there to process them.
Japanese broadcaster TBS said the government believed the situation had become "so dangerous" that it had no choice but to suspend the hunt and recall the fleet.
"If the government does call back the fleet it would mean giving in to anti-whaling activists," the broadcaster said.
Japan is one of three key countries that continue to hunt whales – the others are Norway and Iceland – despite opposition from environmental campaigners and countries including Australia and New Zealand.
Latin American members of the International Whaling Commission recently urged Japan to end its scientific hunts and respect whale sanctuaries.
Australia, meanwhile, has filed a complaint with the international court of justice in the Hague in an attempt to get the hunts banned. A decision is expected in 2013 or later.
Under a provision in the IWC's 1986 ban on commercial whaling, Japan is permitted to kill around 1,000 whales in the Southern Ocean every year for what it calls scientific research.
This year the fleet, comprising four ships and 180 crew members, had planned to kill about 900 minke and 50 fin whales.
But the whalers have been hampered in recent years by clashes with Sea Shepherd activists. Last year they returned to port with 506 minke whales, far fewer than their intended haul.
