An Australian patrol ship tasked with monitoring Japan's whaling fleet has departed from the western city of Perth for waters off Antarctica.
Several vessels are now tailing the Japanese whaling fleet
The Oceanic Viking, a customs vessel, left Stirling Naval Base on Tuesday night on a 20-day surveillance mission.
It will collect photographic and video material for a possible legal challenge against the whalers, Australian officials have said.
Japan's fleet began its annual whale hunt in mid-November.
It plans to kill about 900 minke whales and 50 fin whales by mid-April 2008 as part of what it calls a scientific research programme.
But it has suspended plans to kill 50 humpback whales, amid a storm of international criticism.
Acting against the whalers was one of the new Labor-led Australian government's election pledges.
Japan has backed off from its plan to hunt humpbacks
An Airbus A-319 will also conduct surveillance flights over the fleet.
Evidence from the vessels would be used to help Canberra decide if it could take action against the whalers in international courts, Foreign Minister Stephen Smith said last month.
On Monday he rejected criticism that the government had delayed deploying the ship to ease diplomatic tensions with Japan.
"All of the decisions that were made in respect of the Oceanic Viking have been made on the basis of maximising the potential of 20 days of successful activity," he told journalists in Perth.
There are deep divisions between Australia and Japan on the issue of whaling.
Japan says it kills whales for the purpose of scientific research, something permitted under a clause in International Whaling Commission rules.
But Australia and other nations say the same research goals could be achieved using non-lethal methods, and call the research programme a front for commercial whaling.
Boats from environmental group Greenpeace and the more radical Sea Shepherd group are also tracking the Japanese fleet.
Sea Shepherd says its activists will attempt to intercept the ships.