ADELAIDE (AP) — Australian police conducted searches two anti-whaling vessels that recently clashed with Japanese ships in the Antarctic Ocean in an attempt to obstruct their annual catch, police and activists said.

Federal police with search warrants boarded the Steve Irwin and the Bob Barker, ships belonging to the activist group Sea Shepherd Conservation Society, as the result of a "formal referral from Japanese authorities," a spokesman said on condition of anonymity in accordance with police policy.

He gave no further details, including on what basis the warrant was issued.

The search took place in Hobart, Tasmania — an Australian island lying off the southeast corner of the mainland — where the ships docked Saturday after returning from their pursuit of Japanese whalers in their annual, three-month hunt for the sea mammals.

The hunt is conducted in the name of research although some of the whale meat is then sold in Japan. Jeff Hansen, Australian director of Sea Shepherd, said police had confiscated log books, video footage, charts and laptops, as well as interviewing some of the crew.

He said police would not reveal the reason for their search, and the group had no idea what the Japanese complaints could be.

"We're sort of hoping that they do bring on some sort of investigation or charges," Hansen said. "We'd love to see something get into the courts because the reality is ... (the Japanese) have been the aggressors this year. We'd love to get it in the courts and get their illegal activity into the courts as well."

In the recently ended whaling season, Sea Shepherd vessels and Japanese whalers twice collided. One protest vessel sunk.

In February, activist Peter Bethune of New Zealand jumped aboard one of the Japanese ships with the stated goal of making a citizen's arrest of the ship's captain, while handing over a $3 million bill for the destruction of his protest ship.

He is being held on the ship as it returns to Japan, where he may face charges of intrusion.

The Australian police search Saturday came despite the Australian government's strong opposition to the Japanese whaling.

Canberra has threatened international legal action against Japan unless it stops its annual catch — which is sanctioned by the International Whaling Commission as an exception to its 1986 ban on commercial whaling. Prime Minister Kevin Rudd would not comment directly on the police action but reiterated the government's stance against whaling.

"Either the government of Japan agrees to reduce its current catch from where it is to zero, in a reasonable time, or the Australian government will prosecute this matter in the international court of justice and we would initiate that action prior to the next whaling season," he told reporters in Melbourne.

Australian Greens party leader Bob Brown protested the police search.

"This is outrageous that Australian police are at the disposal of the Japanese whale killers," he said.

Australian police also searched and seized evidence from the Steve Irwin in 2009 but that did not lead to any charges.