Watson is nothing if not a man of action. This was witnessed by Australians in January when Watson's skirmish with Japanese whalers in the Southern Ocean resulted in his stealth boat, the Ady Gil, being destroyed. While Sea Shepherd and its president have only become well known in Australia for their campaign against Japanese whaling, the 59-year-old Canadian has been putting himself between hunters and their prey for 40 years. Having worked with animals for so long, Watson seems to harbour a degree of mistrust for humans. "I happen to think that whales are more intelligent than people," he says. "Certainly their languages are more complex and their communication skills are more complex. "I think there's a lot for us to learn. It's kind of like us going to another planet, finding another intelligent life form and killing them for oil." Watson certainly seems tired of all the focus on human activities. To him, we're just another species among the millions on Earth. It's his belief that the world is already massively overpopulated and he openly advocates reducing the world's population to 1billion by people voluntarily having fewer children.

When speaking with Watson you can sense his frustration, directed not only at those he campaigns against but also against those who aren't willing to adopt his hard-line approach. That's why he reserves some of his most stinging barbs for other environmental groups. Sea Shepherd's conservation work has earned the organisation, and Watson, many celebrity admirers. When he was attacked in his hotel room in 1995, Watson was staying with Martin Sheen. Other supporters include Pierce Brosnan, Sean Penn and Daryl Hannah. But despite the Hollywood support he receives, and the glare of the media limelight, it's clear that Watson is more at home at sea than anywhere else. "It's a total sense of freedom. You're out beyond the bounds of government control and you're one with nature, really," he says. It's kind of like us going to another planet, finding another intelligent life form and killing them for oil. Watson's affinity with the ocean began at the age of six when his family moved to St Andrews, a colonial resort town on Canada's east coast. Watson, the eldest of seven, was born in Toronto in 1950.

When his mother, Annamarie, died in childbirth just after he turned 13, he was left under the care of his physically abusive father. "He was very abusive, so when I was 15 I just turned and defended myself and then left home. I think it was a very liberating thing to do. It's hard to explain but I just suddenly realised that this guy who'd been beating on me, I was bigger than him. So I just turned on him and fought back. Then I left." After working at Expo '67 in Montreal, he drifted into the Canadian Coast Guard and from there into the merchant marine. The skills Watson learned on Norwegian and Swedish freighters would prove very useful in his future career. In 1969, the 18-year-old Watson became the youngest member of the Don't Make a Wave Committee. The group – which was formed to protest American nuclear testing at Amchitka Island off the coast of Alaska – chartered two boats to sail to the islands in 1971, which they renamed the Greenpeace I and the Greenpeace Too. While they didn't stop the 1971 test, their protests drew so much attention that the US Atomic Energy Commission cancelled further testing. In 1972, Watson and the other members of Don't Make a Wave took the name of their ships and became Greenpeace.

From 1972 to 1977 Watson served on the Greenpeace board of directors, as well as captaining and crewing many protest voyages. On one such mission, a 1975 protest against Soviet whaling, something happened that Watson says changed his life forever: "We put ourselves between a harpoon and a whale. They fired the harpoon over our head and hit a female from the pod. She screamed; it was like a woman screaming and there were fountains of blood." Another whale, enraged by a mortal head wound from an exploding Soviet harpoon, made as if to crush the dinghy Watson was in. As a trail of bloody bubbles approached, Watson caught the eye of the whale. "The easiest move at that point was to come right down on top of us. As I looked up at that eye, rising out of the water, an eye the size of my fist; what I saw there really changed my life forever. Because I saw understanding. He understood what we were trying to do. I saw the muscles pull, and he pulled himself back and slipped under the sea to die." The story is clearly well rehearsed. But Watson relates it with genuine feeling. Nearly 35 years later, you can still hear disgust at the whalers and gratitude to the whale in his voice. But by the late 1970s, Watson's aggressive approach to environmental activism was increasingly putting him at odds with his pacifist Greenpeace colleagues. In 1977 he was forced from the organisation's board of directors by a vote of 11 to one. Watson's was the dissenting voice. In the years since, he has had a turbulent relationship with the organisation he helped found.

"It's almost like being in the Russian Revolution with the Bolsheviks. They're trying to rewrite the history. Now they're saying that I'm no longer a co-founder, I was an 'early member'," he says with amusement. "I think that the best thing that ever happened to me was leaving Greenpeace." In 1977, the same year he was forced to exit Greenpeace's board of directors, Watson founded the organisation that would become the Sea Shepherd Conservation Society. A year later the group acquired its first vessel, the Sea Shepherd, a former trawler. Since then, Sea Shepherd's activities have seen them go through seven ships, including the three now in operation. The first Sea Shepherd was scuttled by Watson and his crew before it was due to be given as damages to whalers on the orders of a Portuguese judge. Later ships – Cleveland Amory and Sea Shepherd II – were sold, while Whales Forever was badly damaged in an encounter with the Norwegian navy. Sea Shepherd maintains that the Japanese whaler Shonan Maru No.2 was responsible for the January collision which tore open the most recent addition to their fleet, the Ady Gil. Japan's government-linked Institute for Cetacean Research blames Sea Shepherd. A video of the incident was taken from the deck of Watson's MV Bob Barker and the Australian Maritime Safety Authority is investigating the collision.

His work for the society has taken Watson around the world. He has campaigned against Japanese, Icelandic, Russian and Norwegian whaling in the Pacific, Atlantic and Southern oceans. Since 1979 Sea Shepherd has run a continuous campaign against the Canadian seal hunt. Other campaigns have targeted drift net fishing and the removal of shark fins, with the fish left to die. The organisation's largest current campaign is working with Ecuadorian authorities to protect the Galapagos Islands from poachers and other threats. "The Galapagos is our line in the sand. If we can't save something as beautiful; as profoundly unique, as pristine as the Galapagos, we can't save anything," Watson says. Being at sea for the most part of 30years hasn't stopped the activist from a life outside of work. He's been married, and divorced, three times. His relationship with first wife Starlet Lum, a former Greenpeace activist is amicable, probably because they share a daughter, Watson explains. Their daughter, Lani, is a video game producer who lives in Seattle. Now married, when she was younger she accompanied her father on several voyages. His second wife, Lisa DiStefano, was a Playboy model. The two are not on speaking terms.

"A good example of not judging a book by its cover," Watson laughs. His third wife, Allison Lance, was a member of Sea Shepherd. She now runs her own animal charity devoted to removing introduced species from island habitats. Despite his past failings in love, Watson remains optimistic. "I think I wasn't ready for it [marriage]. I think right now I'd be more ready to devote the time and energy that a relationship requires. Certainly I haven't in the past. "I had to do what I had to do and unfortunately it didn't work out. I'm in a relationship now and I'm having to make some hard decisions. I don't know where that will go," he says.

Long-time friend and Sea Shepherd's director of investigations, Scott West, remains amazed by his energy: "I don't know how he does it. I don't know how he raised a daughter in all of this. It's pretty extraordinary." For this man of action, retirement is not an option. He says that his stubborn streak won't allow him to leave the Southern Ocean until the Japanese do. "I don't see myself retiring, ever. My grandfather worked 'til the day he died at 96. I don't see why anyone has to retire, really. "If you're doing something you love and you enjoy, why would you retire?" The Steve Irwin trails a hauser in attempts to disable the rudder of a Japanese whaling vessel last month and (inset) laser beams aimed at disrupting harpoon fire.

With Terri Irwin after the naming ceremony of the vessel Steve Irwin in Melbourne, in 2007. Watson used the vessel to pursue Japanese whalers. Australian activist Giles Lane soon after he leapt aboard Japanese whaling ship Yushin Maru No. 2 with Benjamin Potts, right, in January 2008. The Ady Gil shortly after it was rammed by Japanese whaling vessel Shonan Maru No. 2, in the background, in Antarctic waters in January. Japanese harpoon ship Yushin Maru No. 1 fires water cannons on Sea Shepherd crew in New Zealand waters last month. Photos: Sea Shepherd Conservation Society. Sea Shepherd locates Nisshin Maru 100 nautical miles from Australia's Davis Station in eastern Antarctica last month.

The Japanese ship Yushin Maru harpoons a whale in the Southern Ocean off Antarctica. It took four harpoon shots to kill the whale.