The last antiwhaling protest ship turned its back on the icy Southern Ocean and headed for Australia on March 11, after a tumultuous season on the high seas.

The Sea Shepherd Conservation Society's ship Steve Irwin began the journey back to the southeastern city of Melbourne overnight after running low on fuel, its captain Paul Watson said.

Watson said this year's protest had been "very successful" for the whales, estimating Japan had only managed to take half of its quota of 935 minke and 50 fin whales.

"This has been our most prolonged campaign down in Antarctica ever, and for five-and-a-half weeks we were able to intervene and stop the whaling activities," Watson said via satellite phone March 11.

Watson said only a few days are left in the season, before icy weather puts a stop to the hunt.