Both sides in the Antarctic whaling conflict are today locked in a marathon pursuit across the Southern Ocean.
Sea Shepherd leader Paul Watson said the anti-whaling group's two ships had covered more than 5000 nautical miles as some of the Japanese fleet's ships tailed them, while others were on the run.
"It's been a hellish week," Mr Watson said from the flagship Steve Irwin. "The weather has been horrendous."
The chase has moved along the coast of the Australian Antarctic Territory and through the Ross Sea to waters off Marie Byrd Land, about midway between New Zealand and South America, and now back towards the Ross Sea.
Mr Watson said the Steve Irwin and the Bob Barker were being followed by two Japanese harpoon ships, alternating with the fleet's security ship, Shonan Maru No.2.
The faster Japanese vessels are able to warn the key factory ship, Nisshin Maru, of Sea Shepherd's location, allowing it to steer clear.
A plan by the Bob Barker to once more shake off its pursuer inside the territorial waters of Australia's Macquarie Island had to be abandoned when the activists' ship was forced away by severe weather.
"On the positive side we have been chasing the Nisshin Maru continuously and, more importantly, we have been keeping the refuelling vessel Sun Laurel on the run to keep it from the Nisshin Maru," Mr Watson said.
"We are in helicopter and drone range of the Sun Laurel. The Nisshin Maru will need to fuel soon.
"This entire fleet has been on the run for over a month and a half, burning lots of fuel and catching very few whales."
However the conservationists are still handicapped by the loss of the fast scout vessel Brigitte Bardot, undergoing repairs in Fremantle, Western Australia, after being damaged in a storm.
"Without the Brigitte Bardot, I can't close the gap on the Nisshin Maru, but we can keep the fleet running," Mr Watson said.
"I have started a fund-raising effort to secure another ship," he said. "I need a third large vessel that can go faster than the harpoon ships. One more ship down here would stop this fleet cold."
Tokyo's Institute of Cetacean Research does not comment on the movements of the whaling fleet. The ICR has reported no recent clash between the two sides.