Militant environmental group Sea Shepherd's leader Paul Watson on Tuesday suggested Japan was involved in his recent arrest in Germany, as he vowed to continue his campaign against whaling.

Watson is on bail while German authorities decide whether he can be extradited to Costa Rica on charges stemming from a high-seas confrontation over shark finning in 2002. He is accused of "putting a ship's crew in danger".

The Canadian national is well known for his pursuit and harassment of Japanese whaling boats off Antarctica which in recent years has significantly reduced the number of animals slaughtered.

"I find it very interesting that the extradition order was put out in October 2011 at exactly the same time that the Japanese brought civil charges against us in a Seattle court," Watson told Australia's Channel 7.

"You know, Japan is spending a lot of money to try and stop us intervening against their illegal whaling activities in the Southern Ocean, and I wouldn't be surprised if Japan was a part of this."

The Japanese Coast Guard said it has tried to "locate, identify or obtain information" on Watson through Interpol but would not comment on the case.

"The government of Japan has not received any official information about Mr Watson's arrest or release. We are not in a position to make a comment," said a coast guard spokeswoman in Tokyo.

Watson, widely known in Australia from where he annually departs on Sea Shepherd's pursuit of Japanese whaling boats, was arrested on the warrant from Costa Rica in Frankfurt on May 13.

Sea Shepherd says it stems from an incident in Guatemalan waters when the organisation encountered an illegal shark finning operation run by a Costa Rican ship called the Varadero.

It claims that while escorting the ship back to port, a Guatemalan gunboat was dispatched to intercept the Sea Shepherd members after the crew of the Varadero falsely accused the Sea Shepherd of trying to kill them.

"I'm under house arrest in Germany so will have to wait and see whether there is a political or legal solution to this and we will fight extradition to Costa Rica. But I think it can be resolved," Watson said.

"Either way, our campaigns will continue with or without me so our ships will again go back to the Southern Ocean in December to once again obstruct the Japanese whaling operations."

Sea Shepherd's annual pursuit of the Japanese whaling fleet has adopted increasingly militant ways to halt the hunt, to Tokyo's irritation.

This year the group hurled stink bombs at the boats on the high seas and used ropes to try to tangle their propellers in a series of exchanges which saw the whalers retaliate with water cannon.