The Australian Government says it intends to honour its promise to send a Customs ship to monitor Japanese whalers.

But the Australian Environment Minister Greg Hunt says he's still working through some of the "operational issues".

"We will have clear monitoring in the Southern Ocean, and I just ask for about 10 days before I make a formal statement on that," Mr Hunt said.

It's understood the Japanese whaling fleet left at the weekend and is expected in the Southern Ocean by the end of the month

Before the election, Mr Hunt repeatedly promised to have a Customs ship in place to monitor activity.

He says he'll provide more details shortly.

"We're just working through some of the operational issues, but the commitment was clear and I stand by it," he said.

The former Australian Greens leader Bob Brown is now the chair of the anti-whaling group Sea Shepherd and says there's no time to waste.

"The decision now has to be made," he said.

"The Japanese whaling ship has left.

"They'll be in the international whale sanctuary before new year."

Australia and Japan are awaiting an International Court of Justice ruling on the legality of whaling.

A decision is expected soon.