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WARNING, GRAPHIC IMAGES: Gruesome video footage obtained from the Australian government shows a controversial Japanese whaling operation in the Southern Ocean.

Ocean conservation group Sea Shepherd obtained the previously unseen footage, which was shot by Australian customs officials in 2008 following a five-year freedom-of-information battle.

The Sydney Morning Herald reported that the Australian government fought to keep the footage secret amid concerns that it could harm relations with Japan.

The Australian Information Commissioner ordered the release of the footage earlier this year.

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Sea Shepherd says that the Australian government sent the customs vessel M/V Oceanic Viking to the Southern Ocean Whale Sanctuary in 2008 to document the operations of the Japanese whaling fleet. “What they saw has been hidden from the public eye, until now,” the group explained on its Whale Defence website.

In graphic detail, the footage shows workers on a ship marked as a research vessel harpooning and killing a Minke whale.

Sea Shepherd has slammed what it describes as illegal Japanese whaling activity. “Despite a global moratorium on commercial whaling in 1986, Japan has been killing whales in the Southern Ocean in the name of ‘scientific research’ since 1987.

“In 2014 the Governments of Australia and New Zealand took the Government of Japan to the International Court of Justice (ICJ) in the Netherlands where their southern ocean whale hunt was deemed illegal.”

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However, the Japanese government continues to send its whaling fleet to the Southern Ocean during each southern hemisphere summer, according to Sea Shepherd. Japan, it said, has a “self-imposed quota” to kill 333 protected Minke whales each year.

The Japanese government has not yet responded to a request for comment on this story.

Japan says that its whaling is for scientific research. A spokesman for Japanese embassy in Australia told the Sydney Morning Herald that the whale "research" program was carried out "in accordance with the International Convention for Regulation of Whaling."

“This footage shows the bloody brutality, cruelty and senseless killing of such beautiful, intelligent and majestic animals," said Jeff Hansen, managing director of Sea Shepherd Australia, in a statement. "These whales are hunted down, before being hit with an explosive harpoon that sends shrapnel through their bodies, while prongs come out so that the whale cannot escape."

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