Anti-whaling group Sea Shepherd says it has driven the Japanese whaling fleet into disarray, hampering its hunt.
The Sea Shepherd says its ships drove the Japanese fleet's factory ship, Nisshin Maru, out of the Antarctic Treaty Zone just before 5pm (AEDT) on Monday, after a 580km chase.
"The Nisshin Maru is on the run and unable to stop and whale in its self-designated whale-poaching grounds," the Sea Shepherd group said in a statement on Tuesday.
The group says the harpoon ships are separated by hundreds of kilometres and presently not hunting whales.
Siddharth Chakravarty, captain of the Sea Shepherd vessel The Steve Irwin, said it was a positive start to its Operation Relentless.
"Within a day-and-a-half we have the entire whaling fleet in disarray," he said.
The Sea Shepherd says its three ships are still in the Southern Ocean and will continue patrols.
"Should the Nisshin Maru attempt to return to the whaling grounds, Sea Shepherd will be ready to once again intercept and shut down their illegal whaling operations," it says.
Sea Shepherd has three ships and about 100 crew - half of whom are Australian - from 21 countries in Antarctic waters to confront Japanese hunting in the Southern Ocean Whale Sanctuary, where commercial whaling is banned.
