Anti-whaling activists are hopeful that Japan's annual whale hunt will be cut short, after the factory ship Nisshin Maru was prevented from refuelling in the Antarctic.
In the aftermath of the clash with Sea Shepherd ships, Nisshin Maru remained in Antarctic waters south-west of Perth this Thursday.
Japan's Institute of Cetacean Research said it had stopped work for the time being because it was too difficult to refuel, according to an ABC report.
"I think possibly they will abandon the season," Sea Shepherd founder Paul Watson told Fairfax Media.
"We are following them and they are just going back and forth at the moment, east and west. But the refuelling tanker is now 60 miles away, and heading north."
Japan has formally protested to Australia over the clash with the Sea Shepherd, urging the Gillard government to restrain the conservation group.
A protest in Tokyo to the Australian and Dutch embassies – both "flag states" of the Sea Shepherd ships – "strongly requested" action to prevent a repeat, a statement said.
Japan accused Sea Shepherd ships of approaching and colliding with Nisshin Maru on Wednesday, in a statement released through Japan's consul general in Melbourne, Hidenobu Sobashima.
RAW VISION: Japanese whaler Nisshin Maru collides with Sea Shepherd vessels Bob Barker, Steve Irwin and Korean tanker Sun Laurel on Wednesday in the Southern Ocean. Vision: Sea Shepherd.
The Japanese government is yet to respond in detail to Sea Shepherd evidence that the during the clash, the 8000-tonne Nisshin Maru hit its own refuelling tanker, Sun Laurel, as well as the group's ships Steve Irwin and Bob Barker.
Their blockade of the refuelling operation held firm, despite the temporary disabling of the Bob Barker. The Steve Irwin was also hit several times by the Nisshin Maru, whose guards threw stun grenades.
After the ships separated, the Bob Barker and the Steve Irwin set off in pursuit of the Nisshin Maru, while the Sam Simon chased the Sun Laurel.
Environment Minister Tony Burke said the Australian Maritime Safety Authority was investigating the clash, which occurred in the Australian search-and-rescue zone.
He also said AMSA would examine whether heavy fuel oil, banned in the Antarctic, was being carried for Nisshin Maru.
The Coalition and Greens stepped up their demands for sending a government vessel south.
"The government says that having a cop on the beat might provoke a fight," said shadow environment minister Greg Hunt. "There's already a fight and and it couldn't be much worse. It's a government living in denial."
Greens leader Christine Milne called on the government to swiftly condemn the violence, and send a naval vessel to monitor the situation.