Anti-whaling activists in the Southern Ocean say they have found the factory ship of the Japanese whaling fleet and hope to drive it from its hunting grounds.
The Sea Shepherd organisation says its ship Steve Irwin found the Nisshin Maru, and together with its sister ship Bob Barker aims to drive it away.
A Sea Shepherd spokesperson says heavy fog lifted on Friday and after several days searching, Steve Irwin's helicopter spotted Nisshin Maru and two harpoon ships Yushin Maru 1 and Yushin Maru 2.
New Zealand co-ordinator Michael Lawry said the Bob Barker is hoping to position itself in Nishin Maru's slipway to prevent the harpoon ships getting whale carcasses aboard, but even if it cannot get into that position, the fleet cannot slaughter more whales while it is being chased.
Mr Lawry said there was evidence in the water that the whales are being processed for market rather than for scientific reasons, and the protesters saw discarded bloody remnants of whales right across the whale sanctuary.
The activists say their presence is expected to drive the Japanese ships out of their self-designated whaling grounds on Saturday.