The Sea Shepherd Conservation Society's anti-whaling ship returned to Australia yesterday, and even the Japanese had to concede its mission was a success.

Japanese authorities admitted the whaling fleet managed to kill only half the number of whales they had intended during their hunt in the Southern Ocean because of harassment by protest ships.

Japan had planned to kill 850 minke whales and 50 fin whales during the summer hunt. Japan dropped plans to also kill up to 50 humpback whales.

Japan's Fisheries Agency refused to comment publicly on the kill, but two Japanese press agencies said officials admitted the catch was between 400 and 600 whales.

Sea Shepherd leader Paul Watson said his information was that only 465 whales were killed.

Click here to read the completes story in the Sydney Morning Herald.