Anti-whaling activists claimed a small victory in their Antarctic campaign Wednesday with the discovery of a Japanese harpoon ship, as one of their boats limped back to Australia badly damaged.

The Sea Shepherd Conservation Society said its Bob Barker vessel found the Japanese harpoon ship Yushin Maru 3 some 200 nautical miles north of the French Antarctic base Dumont d'Urville.

"The Bob Barker has been out at sea for about four weeks and this is the first whaling ship we've come across," second mate Vincent Burke told AFP from the area, which he said was thick with ice.

Burke said his vessel had been searching for the Japanese factory ship the Nisshin Maru in the hope of preventing it from processing any whale meat when it came across the harpoon boat.

He said the Japanese vessel still had its harpoon covered and was therefore unlikely to have started killing any of the giant mammals, and was probably close to the rest of the fleet.

Burke said while he would have preferred to find the factory ship, locating the harpoon boat probably forced the Japanese fleet to keep moving, preventing them from harvesting whales.

"It's a sort of a victory in that we know we're in the right place," he said.

Sea Shepherd activists aim to harass the Japanese whalers during their annual hunt in the freezing waters off Antarctica each year and this year first intercepted the Japanese fleet on December 25 with the help of a drone.

The unmanned plane, small enough to be launched by hand from the deck of the ship, is fitted with cameras and detection equipment.

But the anti-whaling activists suffered a major setback a few days later when the scout vessel, the Brigitte Bardot, sustained major damage when hit by a freak wave in six metre (20-foot) swells.

The activists initially reported that the boat's hull had cracked, but later said that most of the damage was to one of its pontoons, which has since been shored up to enable it to return to port.

The accident prompted another Sea Shepherd vessel, the Steve Irwin, to temporarily abandon the hunt to escort the Brigitte Bardot back to the Western Australian port of Fremantle. Both vessels are expected to arrive on Thursday.

All the crew were reported to be safe and uninjured.

Commercial whaling is banned under an international treaty but Japan has since 1987 used a loophole to carry out "lethal research" in the name of science -- a practice condemned by environmentalists and anti-whaling nations.