Interpol has issued an arrest notice for the Sea Shepherd Society's Canadian founder, who skipped bail in Germany last month over fears of retribution for his ongoing clashes with Japanese whalers.

Paul Watson was arrested at Frankfurt Airport in May on a Costa Rican warrant that claimed he had endangered the crew of a fishing vessel a decade ago.

The environmental activist was released days later on a $320,000 bond and ordered to report regularly to German authorities while Costa Rica's extradition request was considered.

He went missing in late July and Sea Shepherd confirmed he had left Germany, though the group said it had no further information on his location.

Watson himself explained his departure in a message posted on the organization's website, saying he saw no other option after Japanese officials filed their own request for his extradition.

"Costa Rica and Germany have simply been pawns in the Japanese quest to silence Sea Shepherd in an attempt to stop our annual opposition of their illegal whaling activities," he said. "This is not about justice; it is about revenge."

Watson gave little indication of his whereabouts, but suggested he remained at sea.

The Sea Shepherd Society has waged aggressive campaigns to protect marine animals, prompting Japan to label its members terrorists and to seek Watson's arrest for allegedly masterminding violent protests.

Interpol said the information it received from Costa Rica spurred it to ask its 190 members to arrest Watson so the extradition process can resume.

Group defends Watson

Sea Shepherd maintains Watson's arrest was politically motivated.

"The elevation of the attack against our organization and our founder… is not unexpected," Sea Shepherd director Susan Hartland said in a statement posted on the group's website.

"Sea Shepherd fully supports Captain Watson and is at work with our international teams to resolve this politically motivated battle," she said.

The organization said Watson was filming a documentary at the time of the alleged incident in Guatemalan waters in 2002.

The group said it encountered an illegal shark finning operation run by a Costa Rican ship and told the crew to stop and head to port to be prosecuted.

The crew accused Sea Shepherd of trying to kill them by ramming their ship.

Watson parted ways with Greenpeace in 1977 to set up the Sea Shepherd Society.

The group has had a controversial history. Its tactics have drawn praise from supporters and vehement attacks from critics.