Government fisheries observers have reported "brutal" and "needless" killing of blue sharks on surface longline fishing boats.
During one trip, a skipper was noted telling crew to kill "as many as possible" in an effort to reduce population size.
Blue sharks have an unmistakable slender, metallic blue frame. They're a species found right around New Zealand - but four trip reports from observers all detail deliberate maiming and killing of the animal.
"It shows incredibly disrespectful behaviour," says Geoff Keey, Forest and Bird strategic adviser.
Shark scientist Dr Riley Elliot, who spent eight years doing a PHD on the blue Shark, agrees.
"It's gutting, it's emotionally gutting and I feel like our country has let nature down. This isn't how you manage a species."
Under fisheries rules, blue sharks can be put back dead or alive.
"They could simply ban this type of behaviour. They could say you either live release or bring them back as food," says Keey.
The reports, obtained by Forest and Bird under the Official Information Act, detail what observers describe as "brutal" treatment of blue sharks.
Some are "stabbed to death" to get hooks back, while others had their "jaw cut out". One crew member was seen stabbing sharks "needlessly" and then "swinging them by their tails".
Another trip report relays what the skipper told his crew: "He was given the quota and told to use it by killing as many blue sharks as possible to reduce their population size."
The observer's report continues: "Today all eight dead blue sharks that were returned to the sea were killed deliberately and it was not necessary to do so."
"Basically a cull to reduce the population - it's completely wrong," says Keey.
"Pretty sure it's against animal welfare to bring a shark on board and chop its face open to get a $1 hook back - and ecologically a shark is worth far more than $1," says Dr Elliot.
Commercial surface longline skipper Steve Haddock, who's been fishing since he was 16 years old, questions whether action was taken.
"Has MPI been proactive with following through with this so-called brutality? I guess that's the big questions that have got to be asked."
MPI told Newshub "no-one wants to see animals mistreated and any illegal discarding is not acceptable". It said it's now "reassessing" the reports and that getting cameras on boats is a "significant part of addressing these issues".
The reports were from between 2016 and 2021, so the incidents described are not ancient history. However, these are just four reports.
A commercial skipper Newshub spoke to on Wednesday said the incidents make "his blood boil" and it doesn't represent the majority.
Clinton Duffy, Department of Conservation marine species technical adviser, says he doesn't think the practice is widespread.
"We certainly haven't got a lot of evidence for it," he said.
But he says given the gaps in data on blue sharks, it shouldn't be happening at all.
"You sort of hope that this behaviour is a thing of the past, so it's always really disappointing when you come across examples of it."
Haddock says many longline operators have now left the industry due to compliance issues.
"I would like to think that the operators that are left are extremely responsible."
And on his boats, the rules are clear: big blue sharks are always cut free.
Fisheries Inshore New Zealand chairman Laws Lawson told Newshub he's "appalled" by the behaviour.
He says he understands frustration among fishers who incidentally catch shark, but that doesn't legitimise taking such actions.
"Nothing justifies such inhumane and callous action. We are reminding all fishers of the need to act responsibly."