Sea Shepherd has pulled the plug on its decade-long mission to stop Japanese whalers in the Southern Ocean, saying it can’t match the economic and technological power of the government in Tokyo.

The ocean-focused conservationist group has sent ships to harass and hinder Japanese whalers for the past 12 years, but in an announcement on its website says its resources can’t compete with those of its opponents, who are backed by a “major economic super-power”.

Sea Shepherd says Japan’s military is now monitoring the group’s ships, making it difficult for them to get close enough to disrupt or document the whaling.

And Tokyo has also threatened military intervention.

The decision comes after Japan introduced new whaling laws in June that lock in public funding for its whaling program and allow government agencies to dispatch vessels to the Southern Ocean to disrupt the efforts of activists.

At the time, Attorney-General George Brandis said Australia would continue to fight for whale conservation and uphold the global moratorium on commercial whaling.

Sea Shepherd again urged the Australian government to stand up to Japan’s government.

The group also says Australia denying it charity status makes it difficult for it to raise cash to fund its missions.

Sea Shepherd says it is working on a new plan to bring an end to whaling, not only by Japan in the waters between Australia and Antarctica, but also by Norwegian, Danish, and Icelandic whalers.

A ruling by the International Court of Justice in 2014 against Japan’s whaling has been skirted by a revised kill quota.