Hardline whaling opponents attempting to stop Japan's annual whale hunt in the Antarctic said on Sunday they had intercepted and used pilotless drone aircraft to photograph the whaling fleet.
The Sea Shepherd Conservation Society said it located the Japanese factory ship Nisshin Maru off Australia's western coast on Saturday using the drones, the first time this season it has made contact with the whalers.
However, other Japanese ships shielded the vessel "to allow it to escape", Sea Shepherd said in a statement.
"We caught them due west of Perth," founder Paul Watson told Reuters by satellite phone from the ship Steve Irwin. "For the next few days we will be chasing them. We are heading south."
The two drones are equipped with cameras and detection equipment and allow Sea Shepherd to monitor the whaling fleet from a distance, he said.
Watson said Sea Shepherd's three ships were well outside Antarctic waters when the Japanese vessel was seen. The Sea Shepherd waited for the Nisshin Maru after hearing from fishermen it had sailed through the Lombok Strait in Indonesia on its voyage to Antarctic waters.
The Sea Shepherd society's annual attempts to stop the Japanese whale hunt by "direct action" have been widely criticized by other environmentalists and governments, particularly Japan. However, it also has influential supporters.
Watson said sympathizers in New Jersey in the United States contributed to the cost of the two drones.
An international moratorium on whaling has been in place since 1986, but Japan exploits a loophole allowing whaling for scientific purposes to justify its annual hunt.