Japan's fisheries minister has said its Antarctic whale hunt will be cut short following obstruction by a hard-line anti-whaling group.
It is the first time that the fleet is heading home early due to clashes with activists.
Repeated attempts by the Sea Shepherd Conservation Society to block the hunt have caused irritation in Japan.
Japan is one of a small number of countries that hunt whales. The government describes the hunt as an important cultural tradition.
'It has become difficult to secure the fleet's safety,' Fisheries Minister Michihiko Kano told a news conference. 'We have no choice but to cut short our research.'
Sea Shepherd described the decision as a victory for whales and said the movement was proving increasingly effective at disrupting the Japanese fleet's operations.
'We didn't do much differently, but got there early and intercepted them and disrupted them early before they could really begin,' said Jeff Hansen, Sea Shepherd's Australian director.
'Each year we're costing them more and more money. It's a heavily subsidised hunt and they're spending and losing millions so we're very much hurting them in the pocket.
'We'll stay down there in the Southern Ocean, and if they return next season, we'll be there to escort them northward.'
The Japanese fleet, made up of 180 people on four vessels, is heading back from its annual hunt about a month earlier than scheduled.
Fisheries ministry official Shigeki Takaya said the fleet caught 170 minke whales, which is around a fifth of its target.
He said it was unclear how Japan would proceed in future with the hunt.
Japan had suspended the hunt last week after Sea Shepherd started to harass the fleet's mother ship.
