To the Japanese government, they are terrorists. To a US federal appeals court, they are pirates.

To at least one retired Australian rear admiral, their actions are life-threatening, counter-productive, and even have the potential to destabilise the Asia Pacific region.

To many in the global environmental movement, though, the sea-borne activists from the Sea Shepherd conservation group are brave and buccaneering heroes.

Normally each year they engage in what begins as a high seas game of cat and mouse with the Japanese whaling fleet in the vast Southern Ocean, and ends with perilous collisions and clashes.

This year, because the Japanese fleet was late in leaving port, Sea Shepherd was lying in wait. It meant that for the first time in years no whales were killed in January, and that the conservationists were able to scatter the Japanese fleet, making it much harder to conduct its annual hunt.

The Japanese aim was to kill 950 whales for what they have long claimed are "scientific purposes," a definition that allows them to skirt - or flout, according to anti-whaling governments and campaigners - the international moratorium on commercial whaling that came into effect in 1986.

This year, Sea Shepherd believes fewer than 100 whales have been harpooned - a figure which the Japanese do not dispute but did not confirm.

'Embodiment of piracy'

With the whaling season soon to end - low temperatures, long hours of darkness and hazardous ice floes makes it too risky - Sea Shepherd are claiming a victory.

"It's been the lowest whale kill in a decade," says Bob Brown, the former leader of the Australian Greens who is now the head of Sea Shepherd Australia.

Other than pre-empting the arrival of the Japanese fleet, Sea Shepherd believes three strategies have proved particularly effective. First, it has used smaller, faster boats to get between the harpoon ships and their prey. Second, it has tried to prevent the harpoon ships from connecting with the factory ship, the Nisshin Maru. Third, it has targeted a South Korean refuelling ship, the Sun Laurel, so as to starve the fleet of fuel.

In pursuing these disruptive tactics, it has helped that Sea Shepherd has put to sea four ships, its biggest ever flotilla.

Last week, after a series of particularly dangerous confrontations, the group claimed to have brought about a suspension of whaling - an assertion rejected by the Japanese fisheries ministry and also its Institute of Cetacean Research, which organises the hunt.

It also claimed that its ship the Bob Barker came within 15 or 20 seconds of being rolled over after being rammed by the Japanese factory ship Nisshin Maru, and that the Japanese have used water cannons and concussion grenades to deter them. The Japanese argue they are acting in self defence.

The whaling fight is being waged in the courts as well as at sea. This week a three-judge panel of the US Circuit Court of Appeals sided with the Japanese, and ordered Sea Shepherd to stop harassing its ships. In a strongly worded ruling, Judge Alex Kozinski assailed the group's "aggressive and high-profile attacks," calling them "the very embodiment of piracy".

"When you ram ships, hurl glass containers of acid, drag metal-reinforced ropes in the water to damage propellers and rudders, launch smoke bombs and flares with hooks; and point high-powered lasers at other ships," the judge ruled, "you are, without a doubt, a pirate".

The Japanese believe that the ruling vindicates their annual hunt.

"The US Court of Appeals states that the research is legal, and that the fleet has a right to be there," says Glenn Inwood, who runs a New Zealand public relations company, Omeka Communications, employed to speak on behalf of the Japanese.

"What I think it will do is have an effect of Sea Shepherd's American fund-raising. Americans could be reluctant to donate to an organisation that the US justice system regards as pirates."

The only way the whaling will stop is by creating a sufficient body of opinion against it within Japan itself Rear Adm Goldrick

The campaigners argue, however, that the ruling will have no effect, since the court has no jurisdiction in the part of the Southern Ocean where whaling takes place and because Sea Shepherd uses Australian- and Dutch-flagged ships. "It affects Sea Shepherd America," says Bob Brown. "It does not affect us. It also ignores Australian law which prohibits whaling in Australian waters."

More important, he says, is a pending case before the International Court of Justice in The Hague, brought by the Australian government, which considers Japanese whaling to be illegal. In its written submission to the court, the government argued that "the whaling carried out by Japan is commercial, not scientific, and does not fall within that narrow exception".

Just as the clashes at sea have been the angriest since 2010, which saw the sinking of Sea Shepherd's futurist speedboat the MY Ady Gil, there has been an escalation in the exchange of words between Tokyo and Canberra.

Tony Burke, Australia's environment minister, has called the Japanese whale hunt a "disgusting operation." Japan's fisheries minister, Yoshimasa Hayashi, complains that Australian criticism represents "a cultural attack, a kind of prejudice against Japanese culture".

Mr Hayashi compared the Japanese consumption of whale meat with the Australians eating kangaroos. Tellingly, though, he did not cite the usual scientific justification for whaling. Mr Burke was quick to seize upon the omission. "It's significant for them to have abandoned any pretence of a so-called scientific reason," he tweeted.

Fuel-leak fears

Image caption Only an estimated 5% of Japanese still choose to eat whale meat

For both governments there are domestic political considerations to weigh. In an election year, it makes sense for Australia's Labor government to burnish its environmental credentials with a strong anti-whaling message, because it faces a challenge on the left from the Greens.

In Japan, the new Prime Minister Shinzo Abe comes from Yamaguchi Prefecture, which has a strong whaling heritage. His fisheries minister, Yoshimasa Hayashi, was once the secretary general of the Parliamentary League for the Promotion of Whaling.

Geopolitical factors are also at work, according to retired Australian Rear Adm James Goldrick, namely Japan's dispute with China over the Senkaku/Daioyu Islands. "If Japan is seen as being weak with Sea Shepherd," he notes, "how will China interpret this but as a signal to continue its own hard line approach?"

Rear Adm Goldrick, who was the commander of Australia's border protection in 2008 when the new Labor government dispatched a customs ship, the Oceanic Viking, to monitor Japanese whaling, also believes that Sea Shepherd's aggressive tactics are dangerous, counter-productive and environmentally hazardous.

"There's potential for loss of life on both sides and also the risk of puncturing fuel tanks, which in that part of the world would create a huge environmental problem: the release of hundreds of cubic metres of oil in to the sea."

"The only way the whaling will stop is by creating a sufficient body of opinion against it within Japan itself," he notes, and that battle is already being won. With polls suggesting that only 5% of the Japanese population consumes whales, there is thought to be a stockpile of 6000 tonnes of unused meat.

"Sea Shepherd plays to the nationalist tendency in Japan," says Rear Adm Goldrick. "It's the tendency to circle the wagons and start shooting."

The whaling wars, it is clear, are a long way from a ceasefire.