Key Points:

It's easy to like Paul Watson. The teddy-bear-faced 57-year-old has a sea dog's shock of white hair and walrus moustache, a rebel leader's expansive charisma and a poet-cum-PR guru's genius for spin. He is the most affable zealot. He is also at war with most of humankind.

Born and raised in Canada, Watson now has a place in Washington, but the ocean is his real home. He heads the Sea Shepherd Conservation Society, the vigilante marine conservation organisation he founded 30 years ago after he was expelled from Greenpeace, which he also co-founded, for being too confrontational towards sealers.

He calls his fleet, which includes three ships, "Neptune's Navy". This navy's ultimate enemy is anyone who pillages nature - which, in Watson's eyes, implicates humans' numerous destructive habits and appetites.

But the immediate focus is enforcing the flimsy conventions and laws in place to protect endangered marine life.

The current target is the Japanese whaling fleet which departed with a heroes' send-off and government backing last month, bound for four months of whale-hunting in a supposed Antarctic whale sanctuary, where it aims to harpoon 50 fin whales, 50 humpbacks and as many as 935 Antarctic minke whales.

Eleven days ago, the Steve Irwin set sail from Melbourne in pursuit. The campaign is called "Operation Migaloo" after the name given to what is believed to be the world's only living albino humpback, which is probably among the Antarctic pods. (Migaloo is Aboriginal for "white fella").

The Western world, including New Zealand, is roundly denouncing the whaling expedition. Prime Minister Helen Clark has slammed the "deception" of Japan's claim it's for scientific research, saying, "It would just be better if the Japanese [whalers] stayed at home." (A 21-year-old moratorium on commercial whaling by the industry's self-policing body, the International Whaling Commission, doesn't extend to whaling for science.)

A Chilean politician has likened Japan's invoking research to justify killing whales to the Nazis' lethal medical research on human prisoners.

But, so far, only Sea Shepherd, and its disowned cousin Greenpeace, are matching rhetoric with action. Expect dramatic - and controversial - action from Watson's crew.

Watson: "We're not going down there to protest whaling, we're going down there to uphold the international conservation law, doing something Australia and New Zealand should be doing. I can't divulge what our tactics are other than our 30-year record speaks for itself - we've never injured anybody and we've never been convicted of a felony."

Three of the crew are New Zealanders and whale and dolphin ornaments are pinned to walls, among them Maori bone carvings. Four flags fly in the evening breeze: the Dutch flag (the ship is registered in the Netherlands), the Aboriginal flag, the Tino Rangitiratanga flag and the Sea Shepherd flag: a Jolly Roger with a shepherd's crook and Neptune's trident for crossbones.

Further down the dock bob blue-decked white party boats with names such as Carol Dee and Calypso Lady. Wonder Woman and a guy in a lime green suit trip past, en route (you hope) to Christmas parties.

Watson, Auckland brothers Willie and Simeon Houtman, and Ngati Maniapoto singer Mihirangi, who will write an album during the expedition, are in high spirits, too.

They've stocked up on DVDs - the Kiwis have brought the entire series of Bro' Town - food (all vegan), booze and the poker set. It's Mihirangi's first time, but Willie's fourth and Simeon's third Antarctic trip. The brothers have also been on campaigns to the Galapagos Marine Reserve, where Sea Shepherd takes on poachers. Their family and friends, they say, are supportive of their unconventional jobs.

Willie, 24, a ship's engineer, joined the Sea Shepherds in 2002. Simeon, a film-maker, joined two years ago. He'd been working at a television station but realised the nine-to-five life wasn't for him.

"Being on board has changed the way I view society. I was rather naive when I joined, I'd seen the ship and it sounded like an adventure.

"I wanted to save the whales, and I got on and I found out about all the fish that have gone. The way humans treat animals is just appalling and disgraceful."

The crew have full faith in Watson's judgment. Mihirangi: "Paul's such an intelligent man. In 30 years he hasn't done any harm to anybody, I don't think he's about to do so."

Willie: "When we cause damage, we only cause it above the waterline."

The hardest part of the expeditions, says Simeon, is "waiting to find them. Best part is finding them."

Last summer, that took nearly two months. Sea Shepherd had sent two ships after the Japanese, the decrepit Farley Mowat and the 53m-long Robert Hunter (now, in a brilliant PR stroke, renamed Steve Irwin after the late Crocodile Hunter).

Finally, in February, the Hunter caught up with the Nisshin Maru, the gargantuan 8000-tonne factory ship where whales are butchered. The Hunter's crew employed well-honed Sea Shepherd tactics: nailing shut scuppers used to disgorge whale blood, tangling ship propellers with knotted coils of polypropylene, and firing butyric acid - a relatively harmless substance that smells like rancid butter - pie filling and smoke bombs on to the whaler's deck.

The faster whaler escaped when the Hunter pulled away to help in the search for a missing motorised dinghy carrying two crew, who were found alive and well.

Three days later, the Hunter collided with Japanese spotter ship the Kaiko Maru in ice floe-riddled seas, damaging both vessels, and tangled the Japanese ship's propellers. The Farley closed in on Kaiko Maru's other side, and Watson arrested the whaler.

Trouble was, he had no real authority to do so, and no back-up from Australia or New Zealand, the nearest countries. Responding to Kaiko Maru's distress call, Maritime New Zealand ordered Watson to give the ship free passage. Reluctantly, he did.

Earlier in the day, Watson had blustered to media he was considering giving Nisshin Maru a "steel enema" by jamming his ship into its slipway. Conservation minister at the time, Chris Carter, tried to dissuade him via satellite phone. Watson never gave the order for "Operation Asshole".

Instead, low fuel supplies forced the crusading conservationists to abandon their campaign. Days later, an accidental fire in Nisshin Maru's engine room killed a crew member and crippled the ship for two weeks. The Japanese fleet was forced to limp home with barely half its quota filled.

Sea shepherd activists have been labelled extremists and eco-terrorists. More moderate conservationists have complained the society's confrontational style has alienated people from its causes.

Watson impatiently waves this all away. "They can call us eco-terrorists until the cows come home; the fact is that our record proves we are not. I mean, what is an eco-terrorist? To me it's somebody who terrorises the environment, so the Japanese whaling fleet is an eco-terrorist fleet."

Watson calls the Japanese whalers "criminal" for violating a convention on international trade in endangered species, to which Japan is a signatory.

"There's a standard for poor countries and a standard for rich countries. The Patagonia toothfish poachers are criminals and are being dealt with as criminals, the Japanese whalers are criminals and should be dealt with as criminals. For all the rhetoric, there is no difference between what the Japanese are doing and the people who are hunting elephants for ivory. They are poachers."

Humpbacks are in the harpoons' firing line for the first time since 1966, and Watson insists their inclusion is a slap in the face to New Zealand and Australia. "What they're saying is there's nothing you can do about it because your governments don't have the guts to challenge us.

"And Australia is: 'Oh, it's trade relations'. Well, I'll tell you right now, Japan needs Australia more than Australia needs Japan." He laughs.

"Japan's not going to stop buying timber and uranium - I wish they would! - because of whales."

Watson makes the outrageous sound reasonable. He takes the science on the ecological impact of humans to its logical extremes, and he doesn't fuss with shades of grey.

"Right now, we're looking at the complete destruction of the world's fisheries by 2048 because we will have taken everything. The oceans are dying, and they're dying in our time, and we're doing nothing about it."

This is not fringe thinking. Last year, respected journal Science published an article by a group of scientists predicting that, if fishing continues at the present pace, marine eco-systems will unravel and there will be a global collapse of all species currently fished, possibly as soon as mid-century.

Watson is adamant human population growth is out of control. He's contemptuous of humankind's arrogance. "Insects and bacteria are more important than we are because we can't live without them but they can live without us... I place a value on all lives but I think it's arrogance for us to say that we're more important than the very species which make it possible for us to be here. We should give them the respect that's due them."

He believes whales are the most intelligent living beings on the planet. "They have bigger brains and much more complex brains [than humans]... I measure intelligence by the ability to live in harmony with the ecosystem."

Then why don't the whales avoid their hunters?

"Why didn't the Jews avoid being rounded up by the Nazis? When you're going against ruthless individuals, all the intelligence in the world isn't going to save you."

This weekend, the Greenpeace ship Esperanza left Auckland in pursuit of the Japanese whalers. When it finds them, it will film the slaughter and hamper the whalers by getting in the way of harpoons.

Spokesman Dave Walsh says this is the frontline of Greenpeace's campaign, which also involves ramping up international pressure on the Japanese authorities to end whaling.

Watson sneers.

"Greenpeace is just out there making whale snuff-flicks. Nobody kills whales when we show up, and that's the big difference between us and Greenpeace."

Asked about Sea Shepherd, Greenpeace spokeswoman Kathy Cumming turns brusque: "We don't really talk about them."

Sea Shepherd's annual budget is around US$2 million ($2.56 million). Rather than broad fundraising, Watson raises money by giving lectures, advertising the society's work on the internet and appealing to donors directly. Among his A-list supporters are Mick Jagger, Orlando Bloom and Uma Thurman.

Despite his bleak world view, Watson believes it's not too late to save the whales, nor the ocean. Impossible problems, he says, have impossible answers.

"Back in '72 I wrote an article about Nelson Mandela, couldn't get it published anywhere. The guy was a terrorist. Who would have ever thought that Nelson Mandela would be president of South Africa, let alone get out of prison? The answer was impossible. So."

Whaling facts

* The Japanese whaling fleet is run by the government-funded Institute of Cetacean Research in Tokyo.

* In 1986, the International Whaling Commission (IWC) introduced a commercial whaling moratorium, but hunting whales for research has never been banned. Since 1986, Japan has killed almost 10,500 whales, mainly minkes and Bryde's whales, in the name of science.

* The institute's planned take this year is the largest: 50 fin whales, 50 humpbacks, and up to 935 Antarctic minke whales.

* The institute claims the whales it hunts aren't endangered, and that it's necessary to kill them because: stomach contents give insight into whales' dietary habits; analyses of ear plugs is the only accurate way to ascertain a whale's age; whale ovaries reveal the age of maturity.

* Under IWC "no-waste" rules, byproducts from "research" must be processed, so the whale meat ends up in supermarkets and restaurants. However, appetite for what is now a delicacy is fading and there appears to be growing support for the anti-whaling campaigns among the Japanese people.

* Many scientists, governments and campaigners view the research programme as a sham.

* Technically, the Japanese will be hunting in Australian waters and a whale sanctuary, though many countries don't recognise Australian claims to Antarctic waters. Australia has promised to send its navy to monitor the whaling.

* New Zealand Conservation minister Steve Chadwick says this country has no plans to send naval vessels into the Southern Ocean this summer, but will continue exerting pressure on Japan through diplomatic channels to stop whaling.

* Greenpeace estimates Japan's whaling industry is worth A$U75 million ($84 million), compared to Australia's A$300 million ($336 million) whale-watching industry.