Japan's whalers are returning to port with their lowest Antarctic catch, 103 minke whales, after a shortened season marked by heavy clashes with conservation group Sea Shepherd.

The tally, less than half of last year, was disclosed in Tokyo by Agriculture, Forestry and Fisheries Minister Yoshimasa Hayashi, who blamed it on ''unforgivable sabotage'' by the activists.

The whaling fleet arrived in waters south of Australia later than usual, and was pursued by Sea Shepherd south-west of Perth where the conflict climaxed with a refuelling blockade involving multiple ship collisions.

The fleet left in early March, but is believed to have returned briefly after the activists' ships, short on fuel, dropped the pursuit.

Japan has been ''research whaling'' since 1987, facing dwindling catches under Sea Shepherd harassment, and declining interest in whale meat among Japanese consumers.

On its 48-day hunt off the Australian Antarctic Territory this summer, the whalers spent 21 days avoiding Sea Shepherd, The Institute of Cetacean Research said, according to AFP.

Sea Shepherd Australia director Jeff Hansen said this year's campaign would go down as the group's most successful. ''I can't think of more ecological terrorism than going into a protected whale sanctuary, hunting endangered whales, and requiring a fuel tanker to go south into ice strewn waters with all the potential environmental harm involved in that,'' he said.