Sydney  - Japanese whalers in the Antarctic were warned Wednesday that they risked having their vessels rammed or boarded this hunting season.

"We've pretty much got the key to shutting them down," Paul Watson, captain of the Steve Irwin protest ship, told reporters in Hobart, Tasmania. "We just keep on them, keep them running and keep chasing them. As long as they're running, they're not killing whales."

The Steve Irwin, which is owned by the Sea Shepherd Conservation Society, is in Hobart to refuel and take on supplies before attempting to track down the Japanese fishing fleet, which set sail last month.

Last whaling season the Steve Irwin collided with a Japanese harpoon ship and also landed two of its crew members on board a whaler.

Watson said the Australian government, which with New Zealand leads the international campaign to ban commercial whaling, had hindered the Sea Shepherd activists.

"My crew are being detained at immigration for the first time, I was detained at immigration. We aren't allowed to bring in the equipment we need," he told Australia's AAP news agency.

Watson said Canberra had denied permission to bring in bullet-proof vests. Last season he claimed the Japanese had shot at him and that a bullet had lodged in his bullet-proof vest.

Australian Foreign Minister Stephen Smith said last year that Canberra "strongly discourages activity which could be illegal or unsafe activity which could lead to injury or loss of life at sea."

In January, after the two Sea Shepherd activists boarded and were taken hostage, Canberra brokered their release.

Despite an international moratorium on whaling, Japan continues to hunt whales for "scientific reasons." (dpa)