"We are a mile or two behind and matching them for speed. At the moment we are reaching our objective which was to stop them whaling, so there is no need to do anything more than keep them on the run," she said.
But a second activist ship, the Steve Irwin, operated by the Sea Shepherd Conservation Society, was also closing in on the Japanese fleet and her skipper accused Greenpeace of obstructing planned protest actions.
"We tried to co-operate with Greenpeace, but they are not co-operating. They refuse to give their position," Paul Watson, Sea Shepherd's founder, said.
"They claim they don't like our tactics, but they are protesting whaling and we are policing whaling."
Watson, who last year threatened to ram the Nisshin Maru, said he was 80km from the fleet and he would do everything he could to disable the Japanese ships and stop their operations.
|Greenpeace says it sticks to non-violent |
tactics to protect whales [Greenpeace/AFP]
Greenpeace says Sea Shepherd's tactics endanger lives while Greenpeace planned only to disrupt whaling by placing inflatable boats between harpoon boats and the whales.
"We don't believe that the methods they use to try to stop whaling are compatible with our principles of non-violence," Holden said.
"Our actions are peaceful and are not designed to do anything other than defend the whales."
Both Greenpeace and Sea Shepherd have beaten Australia's government in finding the Japanese, with an Australian fisheries patrol icebreaker still en route to monitor the fleet and gather evidence for an international court challenge to the hunt.
Japan's whaling fleet plans to hunt 935 minke whales and 50 fin whales for research over the Antarctic summer.
Last month it said it was abandoning plans to hunt 50 humpback whales after international condemnation and a formal diplomatic protest by 31 nations.
Japan has long resisted pressure to stop scientific whaling, insisting that the practice is a cherished cultural tradition.
The Japanese whaling fleet has killed 7,000 Antarctic minkes over the last 20 years.