Greenland police said they arrested prominent environmental activist Paul Watson on Sunday when his ship docked in the capital, Nuuk. 

The 73-year-old Canadian-American citizen has been known for engaging in direct action tactics such as confrontations with whaling ships out at sea.

Watson has also featured in the reality television series "Whale Wars."

According to his organization, the Captain Paul Watson Foundation (CPWF), more than a dozen police boarded his ship when he arrived in Nuuk to refuel. 

The ship, with 25 volunteer crew members and Watson aboard, was en route to the North Pacific on a mission to intercept a new Japanese whaling ship, the foundation said.

Why was Paul Watson arrested? 

"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 CPWF said in a statement.

"We implore the Danish government to release Captain Watson and not entertain this politically-motivated request," Locky MacLean, a foundation director, said in the statement. Greenland is an autonomous territory of Denmark.

Police said in a statement that Watson would be brought before a district court with a request to detain him pending a decision on a potential extradition to Japan.

In 2012, Watson was arrested in Germany on an extradition warrant issued by Costa Rica.

A week after his arrest in Frankfurt, he was released on bail, on the condition that he would regularly report to authorities until a decision was made on the extradition. 

He left Germany shortly afterward, despite the condition of the release. 
fb/rm (AFP, AP)