With dolphin-hunting season in full swing in Japan, Australian and Japanese environmentalists have launched legal action to try to end the internationally condemned slaughters in Taiji.

Key points: Australian and Japanese environmentalists are suing the local governor to prevent the annual dolphin hunts

Australian and Japanese environmentalists are suing the local governor to prevent the annual dolphin hunts Fishermen have permission to kill up to 20,000 dolphins and small whales a year

Fishermen have permission to kill up to 20,000 dolphins and small whales a year Activists say the hunts breach Japanese animal welfare laws

The hunts became infamous after the 2009 Academy Award-winning documentary The Cove highlighted how fishermen use "banger boats" to drive dolphin pods into a cove, where they are killed for their meat or captured for sale to aquariums.

They are called banger boats because the fishermen bang poles against their hulls to create an underwater wall of sound, which disorients and funnels panicked dolphins into areas where they are easier to catch or kill.

Every year Japanese fishermen have permission to kill up to 20,000 dolphins and small whales as part of what they say are centuries-old traditions.

Australian environmental group Action for Dolphins has teamed up with a Japanese animal rights organisation, Life Investigation Agency, to challenge the legality of the killings.

Under Japanese law, animals are protected as living beings, and "no person shall kill, injure, or inflict cruelty on animals without reason".

A man drives a metal spike into a dolphin's spine. ( Supplied: Action for Dolphins )

The activists have argued that the method used by the fishermen to kill the dolphins, which involves driving a metal rod into their spine and inserting a wooden plug into their open wound to limit the bleeding, is inhumane.

They say that because the dolphins are herded and trapped in the cove, they become "protected mammals" and their treatment consequently breaches the animal welfare laws.

The activists are alleging the prefecture's governor misused his authority by issuing a hunting permit to fishermen they argue violate the law.

Local government insists killings are quick

The Wakayama Prefecture said in a statement on its website it had changed its methods of dolphin killing to reduce the time dolphins take to die.

"The period of time has been reduced to around 10 seconds — a reduction of over 95 per cent," the prefecture said in a statement.

"The wound site is much smaller and the amount of bleeding is negligible," it said.

But Diana Reiss, a marine mammal scientist and expert witness in the case, disputes that.

She said that in footage she had examined, most dolphins took up to five minutes to die.

Under Japanese law, animals are protected as living beings, and "no person shall kill, injure, or inflict cruelty on animals without reason". ( Supplied: Action for Dolphins )

Dr Ross said dolphins were highly evolved, social animals.

"You have them in these coves and then they're [the fishermen] pulling a family member out from the group, tying it and these others are watching as well," the City University of New York academic told the ABC.

"They've all been stressed, most likely in big ways through the whole capture process. Now they're watching individuals being pulled, and often these animals are dying."

The prefecture said the drives had been going on in Taiji for 400 years, with the town flourishing over the years thanks to its whaling and dolphin fishery.

"Whale and dolphins are an integral part of the food culture of the area," the Wakayama website said.

"There are many traditional cultural events throughout the year connected with whales and dolphins, and the industry is indispensable to the local economy."

The ABC has contacted the Wakayama Prefecture and local fisheries cooperative for comment about the legal action.

Officials said it was too early to comment as they were yet to go through the filing and wanted to provide a considered response.

In the past the prefecture has said whales and dolphins are a marine resource which can be harvested in a sustainable manner.

Opposition to slaughter growing in Japan

Every year the fishermen of Taiji drive hundreds of dolphins into a cove, select some for sale to marine parks, release some and kill the rest for meat. ( Reuters: Adrian Mylne )

Right now the hunts are underway, with environmental activist groups like Sea Shepherd trying to monitor the movements of the fishermen.

A lookout near the cove is as close as they can get, and local police are closely watching the activists' movements to make sure they don not try to intervene or trespass.

Sarah Lucas, CEO of Action for Dolphins, said she hoped the legal action would put an end to the hunt, as international pressure from celebrities and activists had failed to stop the practice.

She said it was significant there was a Japanese plaintiff and animal rights organisation behind the case.

"There are more Japanese people who are getting involved as activists, and the case that we're bringing actually has Japanese plaintiffs, which is really wonderful to see," she told the ABC.

"When I first went to Japan, there were mostly foreigners who were protesting. Now, more and more Japanese people know about the hunts and are getting involved as well."

It took six years to find a Japanese law firm and plaintiffs to take the case.

"[It is] not because there wasn't support behind the scenes from Japanese organisations and people," she said.

Experts say the methods used to catch and kill the dolphins are inhumane. ( Supplied: Action for Dolphins )

"[But] to actually go on the record and sign up to be a plaintiff and take legal action or sign your law firm up to go on the record publicly against these hunts is a really big thing to ask of Japanese people.

"They do expose themselves to a lot of opposition, and for a law firm [that can mean] having their other Japanese clients drop out, or for Japanese individuals to be harassed in their own communities."

She acknowledged it would be difficult to escape the criticism of being a foreigner trying to dictate to the Japanese.

"One of the reasons we are taking a legal route is because … public opposition and protests can go so far," she said.

"But when it comes down to the court system, it doesn't matter whether this is Westerners coming in or not. What really matters is — does this violate Japanese law or not? And that's the only issue at stake," she said.

In 2015, Action for Dolphins took the Japanese Association of Zoos and Aquariums to court to ban its members from acquiring dolphins from the Taiji drives.

But aquariums that are not part of the association are still able to take dolphins from the hunt for public display.