Every year, Japanese boats with the word "RESEARCH" stencilled on the side head to the Southern Ocean to hunt for hundreds of whales. And every year since 2005, Paul Watson has used pirate-like tactics to try to stop them.

The ships of Watson's Sea Shepherd Conservation Society nestle up to the back of the large Japanese factory boats that winch whale carcasses up a ramp for processing. Staying so close, Watson says, is a risky but non-violent way of preventing the vessels from hauling in whales.

"We thought the best way to do this was to intervene directly," Watson told The Washington Post. He and other international critics say the whales aren't killed for research at all. "We block their ability to load dead whales and if we do that, they can't hunt."

But now, Sea Shepherd is stopping.

The organisation said the Japanese have used military-grade satellite tracking to evade Watson's whale-hunt-ending ships, which simply can't get close enough.

In the past two years, Watson said, his organisation's ships have only caught glimpses of the Japanese whaling vessels.

"Every time we approached them, they would be just over the horizon," he told the Post. "They knew where we were at every moment. We're literally wasting our time and our money."

It amounts to about $US4 million per expedition, nearly a third of the non-profit's total yearly budget. And that wasted money could be better used to protect other marine animals around the world, Watson said, instead of endlessly chasing Japanese whalers.

The non-profit has been operating in the oceans near Antarctica since 2005, when it took the Farley Mowat, a "battered and slow vessel" out to thwart whalers, according to a news release.

Over the years, it added five other vessels, including one named after "Crocodile Hunter" Steve Irwin, and it claimed more and more successes.

At the same time, it has been engaged in other efforts to prevent poaching and illegal fishing across the globe. The battles aren't just at close quarters in the high seas, they're also in international courts of law.

Watson said one judge deemed him a pirate because of his tactics. Over the past 40 years, Sea Shepherd has engaged in embargoes and sunk several ships in the 1970s and 1980s. That was decades ago, Watson said, but he conceded that even blocking the whaling vessels involves dangerous manoeuvring at close quarters.

Watson was one of the founding members of Greenpeace in 1969, but was expelled seven years later for what the organisation deemed violent actions. He said he took a club away from a man who was attacking baby seals.

A Washington Post story in 1979 dubbed him the "angry shepherd of the seas".

"People sometimes say I have a suicide complex," Watson told the Post's Henry Mitchell for that story, which detailed his attempt to get between whalers' harpoons and their intended target.

"Well, in fact I enjoy being alive, more than most people. But people can't believe a man will risk death to save whales. That's what they can't understand. So they think I'm crazy or that I attach no value to my life."

Watson conceded there's an air of oceanic vigilantism to what he does, but he told the Post that, in his four decades of protecting sea animals, no one has been killed or injured. And he believes some of the people he's trying to combat are violating international laws. The rest, he said, are just outright poaching. He described Sea Shepherd, as an "interventionist anti-poaching organisation".

"Our opposition are criminals," he said on Tuesday. "These people are operating against the law. We shouldn't be out there doing this. The governments of the world should be doing this. We would gladly step aside if they would do what they're supposed to be doing."

The legalised whaling is particularly vexing, Watson said, because the Japanese say they are killing the animals in the name of research.

As The Washington Post's Rachel Feltman wrote in 2015, "most of the whales won't end up in laboratories, but on dinner plates. Japanese officials claim that the specimens will be used to study the health and migration patterns of minke whales, but some argue that these research vessels have never been anything but a way around commercial whaling bans imposed in 1986."

Even then, Wired wrote in 2015, only a small percentage of Japanese eat whale meat. The magazine cited a 2006 poll conducted by the Nippon Research Centre that found that 95 per cent of Japanese people very rarely or never eat whale meat. And the amount of uneaten frozen whale meat stockpiled in Japan has doubled to 4600 tonnes between 2002 and 2012.

And the Japanese government spends about $US50 million a year to heavily subsidise whaling, according to National Geographic. The staunchest advocates say it is a centuries-old tradition - and that no outside nation or international treaty should be able to tell the sovereign nation what it can hunt.

"And just as the whale has become symbolic for environmental groups like Greenpeace, it has, in response, become symbolic for the Japanese, too," the magazine reported.

Kazuhiko Kobayashi, an agronomy professor, told the magazine that the "strong condemnation of whaling by the foreigners is taken as harassing the traditional values".

While Watson's role in the conflict has been paused, he emphasised that his group is not abandoning whales in the south seas. It's simply trying to be practical as it figures out a better way to do it.

It still claimed a victory of sorts, having saved whales for a dozen years, and shone a light on whalers' practices.

"The Japanese whalers have been exposed, humiliated and most importantly have been denied thousands of lives that we have spared from their deadly harpoons," a statement by Sea Shepherd's said.

"Thousands of whales are now swimming and reproducing, that would now be dead if not for our intervention."

Washington Post