Embarrassing new information has surfaced in the debate over wasteful fishing practices.
Newshub can reveal one of MPI's own investigators believes illegal dumping of fish was ignored during an operation in the South Island.
But MPI says it didn't ignore the dumping, it just failed to get the case to court.
New Zealand fish being dumped at sea and thrown overboard so it can be replaced with fresher, higher value catch is called high grading -- and it's part of what a recent research paper says has been ignored for decades.
"It's really putting numbers to what we've known for years: that dumping and high grading is pretty rife within the offshore and inshore industry," Otago University's Department of Marine Research Professor Steve Dawson said.
MPI disputes that -- but its own internal documents, made public in the research, show they've know about the problem for years.
"It's unfortunate a preliminary report has been leaked, but look, we have nothing to hide," MPI's Director of Fisheries Management Dave Turner said.
But Newshub has been leaked additional extracts not published in the research.
One quotes an MPI investigator as saying: "A worst case scenario could see a large international company e.g McDonalds refusing to buy our "non green fish"."
The report went on to say the deliberate non-reporting of a hectors dolphin could have negative effects.
MPI says those comments were made in relation to trials of CCTV technology.
"A dolphin capture was recorded, so it proves the camera technology did work. Also what was found was that there was some discarding happening across that fleet," Mr Turner said.
But it turns out, no one ended up in court. MPI says that's because the cameras caught the offending during a trial.
However, the Ministry's own investigator clearly saw it a different way.
"As I understand it, the Ministry has previously ignored offending [dumping] … because an assurance had been given to vessels prior to observers boarding that such offending would be disregarded and no prosecution taken."
MPI says it takes fisheries offences seriously, but is still trying to gain legal approval to use CCTV footage in court.