A formal complaint made by the Japanese whaling fleet prior to the incident on 6 January regarding the Ady Gil is also under investigation by MNZ.
The Sea Shepherd Conservation Society claims footage proves its anti-whaling protest boat was deliberately targeted by the Japanese whaling ship in Antarctic waters.
It says footage from aboard the protest boat shows the Japanese vessel altered its course to head into the path of the Ady Gil, and ram it.
The Ady Gil sank while under tow on Friday morning.
However, the Institute of Cetacean Research says Sea Shepherd's footage is inconclusive.
Spokesman Glenn Inwood says its footage shows the Ady Gil was powering up and moving forward in the direction of the Shonan Maru No.2.
He says Japan has never deliberately rammed any boat in the Antarctic.
Six crew members aboard the Ady Gil, four from New Zealand, one from Australia, and one from the Netherlands were rescued by the crew of the Sea Shepherd ship Bob Barker.
“The Japanese whalers have now escalated this conflict very violently,” said Bob Barker Captain Paul Watson. “If they think that our remaining two ships will retreat from the Southern Ocean Whale Sanctuary in the face of their extremism, they will be mistaken. We now have a real whale war on our hands now and we have no intention of retreating.”
“This is a substantial loss for our organization,” said Captain Watson. “The Ady Gil, the former Earthrace, represents a loss of almost two million dollars. However the loss of a single whale is of more importance to us and we will not lose the Ady Gil in vain. This blow simply strengthens our resolve, it does not weaken our spirit.”