A Sydney court fined a Japanese firm Aus$1 million (US$709,300) Wednesday for repeatedly killing Antarctic minke whales in an Australian Southern Ocean sanctuary.

The Federal Court found that Kyodo Senpaku Kaisha harpooned the animals in contravention of parts of Australia's Environment Protection and Biodiversity Conservation Act over four seasons between 2008 and 2013.

Justice Jayne Jagot ordered Kyodo to pay fines of Aus$250,000 for each of the seasons, after finding it guilty of wilful contempt of a 2008 injunction against hunting the animals in the area.

"Under Australian law, whales in the Australian Whale Sanctuary in Australian Antarctic waters are fully protected," said Michael Kennedy, national director of Humane Society International (HSI), which initiated the case.

Kennedy said that Jagot had found Kyodo's conduct in breaching the 2008 injunction to be "deliberate, systematic and sustained" and that she was satisfied beyond reasonable doubt that tens, if not hundreds, of whales had been killed during the whaling campaigns.

Despite international disapproval, Japan has hunted whales in the Southern Ocean for years under an exemption in the global whaling moratorium that allows for lethal research.

It cancelled its 2014-2015 Antarctic hunt after the United Nations' highest court, the International Court of Justice, ruled in 2014 that Japan was abusing a scientific exemption set out in the 1986 moratorium on whaling.

Japan said in June that it intends to resume hunts in the Antarctic this year, despite a call by global regulators for more evidence that the expeditions have a scientific purpose.

It makes no secret of the fact that meat from the mammals -- killed ostensibly for research -- is processed into food, and says the whale population in any case is big enough to allow sustainable whaling.

HSI urged the Australian government to use the ruling to redouble diplomatic efforts to ensure Japan is aware the international community would condemn any resumption of whaling in the Southern Ocean.

"We would also expect the Australian government to assess what further legal options are open to it under international law," Kennedy said.

Sea Shepherd Australia, which for years has hounded the Japanese fleet in the perilous waters off Antarctica trying to obstruct their hunt, described the ruling as "an incredible win for the whales".

"The onus for stopping Japan from returning to Antarctica to slaughter whales this year now lies directly with the Australian government," Sea Shepherd managing director Jeff Hansen said in a statement.