From aboard a Sea Shepherd ship, Paul Watson told The Associated Press on Tuesday that his job is to protect whales, and he can't do that if he's in custody.
He said the Sea Shepherd fleet is already in the Southern Ocean.
"I want to stay in the ocean," the 62-year-old said. "I'm not going to be able to do that from some holding cell in Japan."
In July, Watson fled from Germany after being arrested at the behest of the Costa Rican government, which is pursuing him on a warrant that claims he endangered a fishing vessel crew in 2002.
Watson contends the Costa Rican charges were filed because of pressure from the Japanese government and that he eventually would have been extradited to Japan if he had remained in custody.
Shortly after his arrest in May, Sea Shepherd issued a statement saying Watson was filming a documentary at the time of the alleged incident, which took place in Guatemalan waters in 2002.
The U.S.-based group said it encountered an illegal shark finning operation run by a Costa Rican ship, the Varadero, and told the crew to stop and head to port to be prosecuted. The crew accused Watson's team of trying to kill them by ramming their ship.
Watson left Greenpeace in 1977 to set up the more action-oriented Sea Shepherd. The group has waged aggressive campaigns to protect whales, dolphins and other marine animals, prompting Japanese officials to label its members terrorists and seek Watson's arrest for allegedly masterminding violent protests.
The environmental group, based in Friday Harbor, gained fame after being featured in the "Whale Wars" reality TV show.
Sea Shepherd activists use stink bombs and other nonlethal means to interfere with the whalers. The group argues its activities are supported by international law.
This year, the group is calling their campaign "Operation Zero Tolerance" and will feature four main ships, one helicopter and drones.
Watson said the drones will be used for surveillance, reconnaissance, and documentation. He said the drones are military-quality and can fly hundreds of miles head of his ships.
Watson also said it's unlikely he'll return to the U.S., saying American authorities would likely turn him over to Japan.
In February, a U.S. federal judge in Seattle declined to restraint the Sea Shepherd Conservation Society's activities, turning down a request by the Institute for Cetacean Research, the Japanese whalers.
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