Key Points:

A militant environmental group has pledged to harass and intimidate Japan's largest ever whale hunt as its fleet prepares to kill more than 1000 whales in Antarctic waters.

The Sea Shepherd Conservation Society plans to confront the six-ship fleet and disrupt its bid to harpoon 935 minke whales, 50 fin whales and, for the first time in more than 40 years, 50 protected humpbacks.

"If a ship is harpooning whales we see that as an illegal activity and stopping it is no different to ripping a gun out of the hands of a poacher," said international director Jonny Vasic yesterday.

"We're willing to risk our lives so that our kids and grandkids will still be able to see whales in the ocean.

The society's ship the Robert Hunter will leave Melbourne next week and spend a week steaming south into Antarctic waters.

The Japanese fleet left the port of Shimonoseki on Sunday and will be trailed south by the Greenpeace ship Esperanza.

Last year Sea Shepherd's skipper, Paul Watson, threatened to give the whalers "a steel enema" by ramming them with a giant steel can opener attached to his vessel, the Farley Mowat.

The ram was not used in the end, but activists did attack the whalers by hurling acrid-smelling chemicals onto the decks of their ships and using nail guns to fix steel plates over blood drainage portals on the fleets mother ship, the Nisshin Maru.

Sea Shepherd has again threatened direct action, but declined to detail its tactics.

"Everything is on the table as long as it's non-violent," said Vasic. "I would rule nothing out. When we show up, the fleet tends to go on the run because of our reputation. When were pursuing them at high speed, they can't whale."

The Robert Hunter has a crew of 36, representing a dozen nationalities. The Farley Mowat is not taking part.

The ship is being refitted in Bermuda, prior to heading to Canada to disrupt the annual seal hunt.

Japan says it needs to kill whales to conduct research.

Environmental groups accuse Japan of using science as a cover for commercial whaling.