The New Zealand-registered whaling protest ship Ady Gil, which collided on Wednesday with a Japanese whaling ship in Australia's Antarctic waters, has sunk while being towed, New Zealand media reported on Friday.

The damaged powerboat Ady Gil, which belongs to the Sea Shepherd Conservation Society, floats near the Japanese ship Shonan Maru No. 2 after a collision between the two vessels in the Southern Ocean January 6, 2010. Anti-whaling activists accused Japanese whalers of ramming and sinking the high-tech protest boat in the frigid Southern Ocean on Wednesday, but Japan said that its ship could not avoid the collision. Picture taken January 6, 2010. [Xinhua/Reuters Photo]

Paul Watson, spokesman of Sea Shepherd conservation society said the crew of the Bob Barker - the conservation group's newest ship to take to the waters - tried all day on Thursday to salvage the 1.5 million NZ dollars (1.1 million U.S. dollars) vessel.

But attempts to tow the badly-damaged vessel failed and the crew was unable to keep it afloat.

Before the boat sank, the crew removed all oil and fuel to avoid any pollution in the sea.

Watson said the group had no other option other than to try and move the Ady Gil or abandon it.

Sea Shepherd searched Antarctic waters by helicopter for a key Japanese whaling ship on Thursday, renewing its attempts to find and harass the whalers into giving up their hunt, Watson said.

New Zealand and Australia announced investigations on Thursday into the crash.