Three anti-whaling activists boarded a Japanese vessel off southwest Australia on Sunday as part of a campaign to stop whale hunting in Antarctic waters.
The three Australian men boarded the Shonan Maru No. 2 in early morning darkness as it tailed the Sea Shepherd Conservation Society's flagship the Steve Irwin, the conservation group said in a statement.
The three activists, who are members of an environmental group, said they were helping Sea Shepherd "end illegal whale poaching."
The whale hunts, which Japan says are for scientific purposes, are allowed by the International Whaling Commission as an exception to the 1986 ban on whaling. But opponents say they are a cover for commercial whaling because whale meat not used for study is sold for consumption in Japan.
Glenn Inwood, spokesman for Japan's Tokyo-based Institute of Cetacean Research, which sponsors the annual whale hunt, confirmed that the three had boarded the vessel and were being questioned. The activists were not injured.
"I would describe them as volunteer detainees," Inwood said.
Pete Bethune, a Sea Shepherd activist, boarded the same Japanese ship in 2010. Bethune, a New Zealander, spent five months in a Japanese jail before being convicted of an array of offenses and deported.
Sea Shepherd founder Paul Watson, captain of the Steve Irwin, called on Australia's government to prevent the three Australian citizens from being taken to Japan.
"Japanese vessels have no right to take prisoners in Australian waters," Watson said.
But Attorney General Nicole Roxon said the boat was boarded outside Australia's legal jurisdiction.
"At this stage, the boat hasn't sought to come into port," Roxon told reporters. "We may, of course, in the coming days want to have discussions to do just that if it's one way to be able to get these three Australians safely back to Australia."
Sea Shepherd said the three activists reached the Japanese vessel _ a former harpoon boat that now performs a security role for the whaling fleet _ in two small boats and climbed over its rails.
They came with the message, "Return us to shore in Australia and then remove yourself from our waters," Sea Shepherd said.
The three activists are members of the environmental group Forest Rescue.
"Forest Rescue is making a stand to assist Sea Shepherd Conservation Society in their campaign to end illegal whale poaching in the Southern Ocean Whale Sanctuary," Forest Rescue said in a statement.
The statement names the three men as Geoffrey Owen Tuxworth, 47, Simon Peterffy, 44, and Glen Pendlebury, 27. They are all from Western Australia state.
The Shonan Maru No. 2, which collided with the Sea Shepherd speed boat the Ady Gil in 2010, tailed the Steve Irwin as it escorted the anti-whaling vessel Brigitte Bardot to the Australian port of Fremantle last week for repairs. The Brigitte Bardot had been damaged by a rogue wave.
Japanese surveillance of Sea Shepherd vessels helps the fleet avoid the protesters as the whalers go about their annual hunt.
Watson said the three activists had hoped to divert the Shonan Maru No. 2 off the Steve Irwin's tail as it searched for the whalers.