The environmentalist group Sea Shepherd has called off its annual pursuit of Japanese whaling ships in the Southern Ocean, according to the group’s founder, who said it cannot keep up with Japan’s surveillance technology.

“What we discovered is that Japan is now employing military surveillance to watch Sea Shepherd ship movements in real time by satellite,” the group’s founder, Paul Watson, said in a statement. “If they know where our ships are at any given moment, they can easily avoid us.”

Sea Shepherd, a self described “eco-vigilante” group founded in 1977, has spent years patrolling the remote Southern Ocean, investigating and documenting illegal fishing and whaling operations, putting it directly at odds with Japanese vessels. In addition to filming the operations, the group uses confrontational tactics that include shooting water cannon and stink bombs at the Japanese vessels.

Mr. Watson maintains that his group acts within the law. “We never caused a single injury to any person in all of these years,” he said in an interview. “The criminals are quite plain to see.”