Sea Shepherd activists have found and blockaded Japan's key factory ship Nisshin Maru in the Antarctic.
Last week the Nisshin Maru gave Sea Shepherd vessels the slip in thick ice and was able to refuel, breaking a month-long grip by the activists on the whaling fleet.
The conservationists said their scout vessel Gojira located the Nisshin Maru on the far north-eastern tip of the Ross Sea overnight.
In a skirmish through pack ice, the Australian-flagged Gojira kept the factory ship engaged while a second Sea Shepherd vessel, the Bob Barker, caught up, the group said in a statement.
"At 0400 hours, the Bob Barker placed itself immediately aft to the stern slipway of the Nisshin Maru to block any further attempts to offload dead whales," the group said.
"The Bob Barker is now easily pursuing the Nisshin Maru through thick pack ice with the Gojira continuing to skirt around the ice looking for harpoon vessels."
Japan's Institute of Cetacean Research said the Gojira deployed a propeller fouling rope, approached dangerously close to the Nisshin Maru's bow, and navigated across the mother ship's course.
Its crew also launched multiple glass bottle projectiles, smoke bombs and incendiary devices including a parachute-type flare towards the Nisshin Maru, the institute said.
"The institute ... strongly condemns the Sea Shepherd Conservation Society and its continued dangerous and violent actions against Japan's whale research vessels in the Antarctic."
Gojira's skipper, Locky MacLean, said the Nisshin Maru at one point bore down on his fast multi-hull vessel when it was stopped amid ice, and turned away only from 40 metres' distance when he fired a flare signal.
The Nisshin Maru was in the process of flensing a whale when it was located, but the activists say that if the Bob Barker can hold its position on the factory ship's stern, no whales can be loaded, and whaling operations will be effectively shut down.
Sea Shepherd's other ship, the Steve Irwin, left Wellington yesterday after refuelling and is likely to take five days to reach the scene.
Andrew Darby is the Hobart Correspondent for The Sydney Morning Herald and The Age.
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