In the 2000s and 2010s the activists played a rough high-seas game of cat and mouse with Japanese ships as they sought to slaughter hundreds of whales every year for "scientific purposes".

Sea Shepherd founder Paul Watson, 73, is in custody in Greenland and Japan wants to extradite the US-Canadian campaigner over the alleged damage and injuries caused. A court hearing on his continued detention was due later Wednesday.

The activists "tried to wrap ropes around our propeller, and all kinds of things, which escalated year by year," Takeda, 54, told AFP in Tokyo.

"Sea Shepherd's ship rammed into the (Japanese whaler) Shonan Maru No 2 and sank. No one died but I think it was close," he said, referring to Sea Shepherd's high-tech Ady Gil which went down in 2010.

Takeda, who now works on land for Japan's whaling company Kyodo Senpaku, said he witnessed another collision close-up.

"I had never expected the activists would go be extreme... the Japanese ship was leaning over so badly that I thought it might capsize," he said.

Over the years "on our side some people suffered injuries and there were no deaths. But that kind of collision could have led to a serious situation," he said.

In many incidents that often continued through the night, the group "threw bottles of butyric acid," which injured Japanese crew members with chemical burns, Takeda said.

"I think there should be various opinions including anti-whaling, but appealing to violence is wrong," he said.

- 'Terrorist actions' -

Sea Shepherd has said that it was their vessels that were repeatedly rammed by Japanese ships, not the other way around, amongst other dangerous tactics.

The Japanese government has said very little about the Watson case, confirming only that it has sought extradition and that the decision was up to Denmark, which administers Greenland.

But the president of whaling firm Kyodo Senpaku told AFP that he was all in favour of Watson being brought to Japan over Sea Shepherd's "terrorist actions".

"No matter what argument they use, what they did were terrorist actions... It is normal that he (Watson) should come to Japan, face a fair court ruling and receive punishment for his crime," said Hideki Tokoro.

"If we let him go again, he will come to Japan and sabotage our work again, he will put us at danger again," Tokoro said.

Watson is no longer part of Sea Shepherd and Tokoro said that his new organisation, the Captain Paul Watson Foundation (CPWF), is "simply a fund-raising business."

Since Watson's detention in July, the group has raised "a great deal of funding, which is their business. What they are doing is not anything to do with environment protection," he said.

- 'Mother ship' -

Japan eventually halted its hunts in the Antarctic and North Pacific and since 2019 has only caught whales in its territorial waters and exclusive economic zone.

In May, Japan launched a new "mother ship", the Kangei Maru, to butcher the 200 marine mammals that its fleet plans to catch this year and store their meat.

The CPWF says that its vessel the John Paul DeJoria was on its way to intercept the Kangei Maru when Watson was arrested.

Activists believe that in building the new ship, Japan intends to resume whaling in the Southern Ocean, but Tokoro denied this.

"As far as we operate commercial whaling, we will never, ever go to the southern waters," he told AFP.

- 'Melt-in-the-mouth' -

Japan hunts after Bryde's, minke and sei whales, and recently expanded the list to include fin whales, the second-largest animal species on the planet after the blue.

Tokoro's company has so far caught four fin whales, but will not likely to meet the catch limit of 59 set by the government because the catch approval was "very late," he said.

After the first one, which weighed more than 50 tons, was caught on August 1 the company organised a tasting event.

"It was really delicious. Really delicious. They live in the cold ocean, so the fat is very soft," Tokoro said.

"Bryde's whale has a bit of a crunchy texture, but fin whale meat melts in your mouth. You don't need to chew it at all."