Photo/Illutration Paul Watson, founder of the anti-whaling group Sea Shepherd Conservation Society, attends an animal rights rally in Berlin on May 23, 2012. (REUTERS)

COPENHAGEN--Anti-whaling activist Paul Watson will remain in detention in Greenland while Denmark decides whether to extradite him to Japan, police in the autonomous Danish territory said on Monday.

U.S.-Canadian Watson, who turned 74 on Monday, is the founder of the Sea Shepherd conservationist group and the Captain Paul Watson Foundation. He was taken into custody by police when his ship docked at the port of Nuuk on July 21.

Watson will remain in detention until Dec. 18, police in Greenland said in a statement, adding that he had appealed the Nuuk court's decision.

Japan issued an international warrant for Watson's arrest over a decade ago. He is wanted on charges of breaking into a Japanese vessel in the Antarctic Ocean in 2010, obstructing business operations, and causing injury and property damage.