"We know they bought a 150,000-dollar ship-tracking programme, so we suspect they can see us through the satellites," said Watson, who has been searching for the whalers in the Southern Ocean for three weeks.

"We're taking some steps to try to avoid the satellites. We know what time they fly over, so we, you know, try to hide behind an iceberg. But the thing is we are really at a disadvantage."

Watson and his Sea Shepherd Conservation Society are hunting the six Japanese whalers with the 54-metre (177-foot) Farley , a second, faster ship, the Robert Hunter, a helicopter and a total of 70 crew from 14 countries.

The Canadian-born activist, who has been accused in the past of using violent tactics in his conservation efforts, has threatened to use a ram to punch holes in the whalers and force them back to port.

But time is running out, and it could be Watson's expedition that is forced to return to port to refuel if it does not find the Japanese fleet within the next two to three weeks.

Watson's offer of a reward for information on the location of the fleet was apparently prompted by the New Zealand government's release last Friday of footage of the Japanese ships harpooning and cutting up whales.

New Zealand opposes Japan's whaling but has refused to disclose the exact location of the fleet, with Environment Minister Chris Carter having expressed concern about Watson's threats against the whalers.

Watson told AFP that New Zealand's refusal to provide the fleet's geographical co-ordinates "makes them complicit in a Japanese crime".

He said he hoped somebody with access to the information -- "either in New Zealand or through satellite programmes" -- would provide it in return for the 25,000-dollar reward.

"We are actually able to cover large areas with the two ships and the helicopter but we haven't been having much luck," he said.

The International Whaling Commission imposed a moratorium on commercial whaling in 1986 but Japan has continued hunting for what it calls scientific research.

Critics reject this claim, and Japan makes no secret of the fact that the meat from the hunt winds up on dinner plates.

The Japanese ships are on an expedition during the Southern Hemisphere summer this year to kill about 850 minke whales and 10 fin whales, the Japanese Fisheries Agency has said.

The whalers will also be hunted by the international conservation group Greenpeace, whose fastest ship, the 72-metre Esperanza, left New Zealand for the Southern Ocean last Friday.

Spokeswoman Sara Holden told AFP from on board the Esperanza that they would not reach the whaling grounds for about a week, but added: "We are confident that we will find them."

The Esperanza plans to launch small inflatable boats, which will attempt to position themselves between the whaling ships and their prey, preventing the Japanese from firing their harpoons.

Related Links
GPS Applications, Technology and Suppliers