The environmental activist group Sea Shepherd has returned to land after its longest-ever anti-whaling campaign in the Southern Ocean, claiming to have saved more than 750 whales from Japanese whalers.

Sea Shepherd's ships Bob Barker and Steve Irwin docked in Wellington, New Zealand, and Hobart, Australia, on Saturday after 94 days at sea, ending the group's 10th annual campaign against the Japanese harpoon fleet.

There were three high-seas confrontations during the campaign, described by Sea Shepherd as "ambushes" by the Japanese, and Bob Barker captain Peter Hammarstedt claimed the season had been a success.

"Although the whale poachers have not yet released the number of whales they have killed this season, we are confident that they have not even reached one quarter of their bogus self-allocated quota, and estimate that our efforts have saved over 750 whales," he said.

The group did not offer any details to support their claim and the Japanese fisheries agency was not immediately available for comment.

Sea Shepherd said this year's campaign, which began on Jan 5, had been its longest in the Southern Ocean.

"These whale poachers, heavily funded and backed by the government of Japan, have thrown absolutely everything at us, and we have come out on top," said Jeff Hansen, director of Sea Shepherd Australia.

During the season, the conservation group said the Japanese had twice been exposed the butchering of minke whales poached from the Southern Ocean Whale Sanctuary.

Japan catches the animals there under a "scientific research" loophole being challenged by Australia in the International Court of Justice, with a ruling due this year.

Steve Irwin captain Sid Chakravarty said the harpooners had used "aggressive" tactics to flee from the activists but "they could not hide from us".

Sea Shepherd estimates that it has saved 4,500 whales from slaughter in nine previous Southern Ocean campaigns.