WELLINGTON, New Zealand >> Investigators looking into a collision between a Japanese whaler and a high-tech protest boat on the high seas off Antarctica earlier this year said that the captains of both vessels were to blame.

The Sea Shepherd Conservation Society had accused the Japanese ship of deliberately ramming its futuristic, rocket-shaped boat, the Ady Gil, on Jan. 6, slicing the bow off the speed boat and eventually causing it to sink. The whalers denied it, saying the Ady Gil’s captain deliberately put his vessel in their ship’s path.

The clash was the most serious in the several years that Sea Shepherd has sent vessels into far southern waters to try to harass the Japanese fleet into ending its annual whale cull.

Government safety agency Maritime New Zealand said in a report released Thursday, New Zealand time, that the captains of both the Ady Gil and the whaler, the Shonan Maru No. 2, “were responsible for either contributing to, or failing to respond to the ’close quarters’ situation that led to the collision.”

It “found no evidence that either vessel master had deliberately caused the collision,” but said there was “a failure by both masters and the crew(s) … to appreciate and react appropriately to avoid colliding.”

The Ady Gil, captained by New Zealander Peter Bethune, had 11 feet (3.5 meters) sheared off its bow in the collision in frigid waters about 180 miles (290 kilometers) north of Antarctica. The boat’s six crew members were rescued and the hulk later sank while under tow.

The Shonan Maru No. 2 suffered no apparent damage.

Maritime New Zealand director Catherine Taylor said the Japanese skipper initially had responsibility for keeping his vessel clear of the Ady Gil as the overtaking vessel.

“He had ample opportunity to avoid the close quarters situation that subsequently developed, but failed to do so,” she said. He also “failed to take positive and ample action to avoid colliding with Ady Gil.”

But once the vessels were at close quarters, the captain of the Ady Gil “failed to respond by taking appropriate evasive action — choosing instead to maintain his course and speed, which allowed the close quarters situation to develop into a collision risk,” Taylor said.

The protest ship also was found to have failed to maintain a proper lookout.

Bethune, the Ady Gil skipper, said he was happy the report acknowledged his vessel had right of way over the Japanese ship.

“They’re the boat that ran the red light,” he told The Associated Press, adding that the report confirmed the Shonan Maru No. 2 had made an abrupt turn seconds before the impact.

“As I look at it he was intending to take our boat out and that’s what ended up happening,” he said.

He admitted failing to keep a proper lookout, but said when an 18-ton vessel is facing an 800-ton vessel “you don’t expect them to turn in and run you over. The Japanese just disobeyed all of the rules.”

Japan’s Institute of Cetacean Research, which sponsors Japan’s whale hunts, said it had no comment on the report. Officials at Japan’s Fisheries Agency said they needed time to study the report before commenting.

In mid-February, Bethune was taken into custody after secretly boarding the Shonan Maru No. 2. He said he wanted to make a citizen’s arrest of the ship’s captain and hand over a $3 million bill for the destruction of the Ady Gil.

The Institute of Cetacean Research called Bethune’s actions “a form of piracy,” and the whaling ship returned to Japan with him aboard. He spent five months in a Japanese jail before being convicted of an array of charges and deported.

Bethune, who became estranged from Sea Shepherd after his arrest, has alleged that the Ady Gil could have been salvaged after the crash but that the group ordered him to deliberately allow it to sink to garner support for its anti-whaling campaign. Sea Shepherd countered that Bethune made the decision to let the ship sink.