The Federal Government is under pressure to send a Customs ship to the Southern Ocean now to monitor the Japanese whaling fleet.

The Australian Greens are questioning the whereabouts of the ship which the Government promised would monitor the fleet this summer.

Greens Senator Peter Whish-Wilson claims it is being used for a border protection operation at Christmas Island.

Sea Shepherd Australia has begun its summer campaign against the Japanese with one of its ships leaving Hobart for the Southern Ocean.

Senator Whish-Wilson joined hundreds of people lining a Hobart pier this morning to wave off the Bob Barker.

He questioned whether the Government would honour its pledge.

"We have a purpose-built Customs vessel that costs the taxpayer $150 million," he said.

"It is purpose-built for the Antarctic, it is ice-rated, it is sitting off tropical waters on Christmas Island. It needs to be off Macquarie Island, not Christmas Island.

"I've got a photo of it during the week sitting in tropical waters. What's it doing there?

"[It needs to] not just monitor, but also to uphold Australian law, which is very clear that whaling is illegal in these waters."

But the Federal Environment Minister Greg Hunt says he intends to honour his promise and has indicated an announcement is imminent.

Anti-whaling campaign marks 10th year

The Bob Barker is one of three ships Sea Shepherd is sending south to frustrate the efforts of Japanese whalers.

Skipper Peter Hammerstedt says the activists forced the Japanese whalers to abandon their season early last year.

"The Japanese whaling fleet intends to kill 1,035 whales of which 50 are endangered fin whales and 50 are endangered humpback whales, the very same whales that frequent the shores here off of Australia," he said.

"Our intention is to once again intercept the Japanese whaling fleet in the Southern Ocean whale sanctuary and to do everything that we can."

It is the 10th year the society has run the anti-whaling campaign.

This season could be the last, after Australia took Japan to the International Court of Justice to stop what the Japanese maintain is a scientific operation.

A ruling on the court case could be delivered in the middle of the season.