Paul Watson goes to extreme lengths to protect whales. Japan says he belongs in jail.

Greenland police said they apprehended veteran environmental activist and anti-whaling campaigner Paul Watson on an international arrest warrant issued by Japan.

Mr. Watson, a Canadian-American citizen, is a former head of the Sea Shepherd Conservation Society whose direct action tactics, including high-seas confrontations with whaling vessels, have drawn support from A-list celebrities and featured in the reality television series “Whale Wars.”

He was arrested on July 21 when his ship docked in Nuuk, Greenland’s capital, a police statement said. He later appeared before a district court to look into a request to detain him pending a decision on his possible extradition to Japan, the statement said.

On July 22, the Captain Paul Watson Foundation said in an emailed comment the veteran environmentalist would be detained in Nuuk at least until Aug. 15, following the court’s decision, to give the Danish justice ministry time to investigate the case and possible extradition. He faces a maximum sentence of 15 years in prison in Japan, according to the foundation.

His foundation also said the Greenland court wouldn’t allow Mr. Watson’s release on bail as he was considered a flight risk.

The foundation described more than a dozen police officers boarding the vessel and leading Mr. Watson away in handcuffs when it stopped to refuel. The foundation said the ship, along with 25 volunteer crew members, was en route to the North Pacific on a mission to intercept a new Japanese whaling ship.

“The arrest is believed to be related to a former Red Notice issued for Captain Watson’s previous anti-whaling interventions in the Antarctic region,” the foundation said in an emailed statement on July 21.

“We implore the Danish government to release Captain Watson and not entertain this politically-motivated request,” Locky MacLean, the foundation director, said in the statement.

Neither the Japan Coast Guard nor Japan’s Foreign Ministry, which had issued the international warrant for Mr. Watson, confirmed they are negotiating Mr. Watson’s handover. However, the coast guard, the primary investigative authority in Mr. Watson’s case in Japan, said July 22 that officials were on standby if a handover is ordered.

Greenland is an autonomous territory of Denmark. Japan does not have an extradition treaty with the European country and it is unknown if or when Mr. Watson would be handed over.

It’s not the first time his tactics brought him head-to-head with authorities. He was detained in Germany in 2012 on a Costa Rican extradition warrant but skipped bail after learning that he was also sought for extradition by Japan, which has accused him of endangering whalers’ lives during operations in the Antarctic Ocean. He has since lived in countries including France and the United States.

Mr. Watson, who left Sea Shepherd in 2022 to set up his own organization, was also a leading member of Greenpeace, but left in 1977 amid disagreements over his aggressive tactics.

According to his foundation, Mr. Watson’s current ship, the M/Y John Paul DeJoria, was due to sail through the Northwest Passage to the North Pacific to confront a newly built Japanese factory whaling ship, “a murderous enemy devoid of compassion and empathy hell bent on destroying the most intelligent self-aware sentient beings in the sea.”

This story was reported by The Associated Press.