Sea Shepherd, notorious for its aggressive tactics, has two ships and one helicopter stalking the Japanese vessels in the Ross Sea, south-east of Australia. Japan, which has been whaling in the area since mid-December, aims to catch up to 935 minke whales and 10 endangered fin whales this summer, supposedly for scientific research purposes.
The Canadian-based conservation group, which Japan has denounced as an "eco-terrorist" organisation, is promising a major confrontation. But first it has to find the fleet, which it says is using a new satellite tracking system to elude it.
Sea Shepherd has offered a $25,000 (£13,000) reward to anyone who can provide the ships' coordinates. It has also appealed to the New Zealand government, whose air force has filmed the fleet, it believes. But it has not yet received "anything conclusive", Paul Watson, the group's president and founder said yesterday.