Maritime New Zealand says its report into the collision of a whaling ship and an anti-whaling protest boat in the Southern Ocean represents a black mark against the masters of both vessels.
The report says both the whaling ship, the Shonan Maru 2, and the New Zealand-registered high speed protest boat, the Ady Gil, were responsible for the collision.
The damaged Ady Gil was cast adrift two days later, and sank.
The report says there is no evidence to suggest either master intended the collision to occur, but both failed to take appropriate action to avoid it.
The report says the Shonan Maru 2 failed to maintain a safe speed and keep clear of the protesters in a close quarters situation, while the Ady Gil did not maintain an effective lookout or enough speed to avoid the whaling ship.
Maritime New Zealand says it decided not to prosecute Ady Gil skipper, New Zealander Pete Bethune, and it has no jurisdiction over the master of the Shonan Maru 2.
Director Catherine Taylor says rather than seeking prosecution, the best safety gains can be made by publishing the report internationally.
MNZ satisfied with data
Maritime New Zealand says its investigation was robust and thorough, despite not interviewing the Japanese whalers involved.
The report says the responsibility for interviewing the whalers lay with the Japanese Coastguard, which did not take statements from the crew.
MNZ director Catherine Taylor says the Coastguard provided the investigation with video footage and voyage data from the Shonan Maru 2.
"We're satisfied that with 24 hours of video footage - a lot of data from the vessel -that the conclusions we have drawn are appropriate and accurate."
After boarding the Shonan Maru 2 to protest against the crash, Bethune was arrested and spent four months in a Japanese jail.
Bethune says he is reasonably happy with the findings but would have liked to see the report to put out a percentage of blame, similar to an insurance claim.