Fast food giant McDonald's has been being urged to stop sourcing its fish from New Zealand waters following the leak of a confidential report which revealed the unreported capture of a rare dolphin.

The leaked report of an investigation in 2013 by the Ministry for Primary Industries, titled Operation Achilles, also revealed New Zealand fishing boats had illegally dumped large amounts of healthy fish -- a finding which prompted the ministry to launch an inquiry this week.

McDonald's sources some of its fish for the Filet'O'Fish burger from New Zealand waters, and environmental campaigners are now urging it to drop New Zealand fish from its menus.

"We are not attacking McDonald's," Nabu International spokeswoman Barbara Maas said. "They have a huge opportunity here to do the right thing and bring about some real change in the New Zealand fishing industry -- they could say they saved the Maui's dolphins, and how good would that be for their brand?"


The group will soon launch a campaign which includes billboards with the message: "Buy New Zealand Fish Get Dead Maui's Dolphin Free."

The BBC reported that 15 per cent of McDonald's' fish products were made from hoki. McDonald's told the BBC that 8 per cent of its hoki came from New Zealand fisheries, and that this fish stock had been certified by the Marine Stewardship Council as sustainable.

"We understand the importance of protecting marine wildlife, especially endangered species that share the ocean with the fish we use on our menu," the company said in a statement.

"That's why we're proud of our global commitment to only source fish from a Marine Stewardship Council certified sustainable fishery, including in New Zealand."

An academic report released this week alleged that New Zealand fisheries had caught 2.7 times more fish than official records showed, due to illegal dumping of unwanted species and failure to declare catch.

It was dismissed by the Government and the seafood industry, who said it was not credible and would not withstand peer review.

The report included references to the Operation Achilles investigation, which was subsequently leaked.

The investigation was sparked by the capture of two Hector's dolphins -- a close relative of the Maui's dolphin -- by a commercial fishing vessel in December 2012. One of the dolphin captures was not reported to authorities by the unnamed vessel's captain.


In reviewing footage of the accidental capture, investigators witnessed the vessel discarding numerous healthy fish. They widened their investigation to five other vessels, four of which were also found to be illegally discarding fish in full view of ministry observers and mandatory onboard cameras.

The report urged the ministry to take the fishing companies to court, but no action was taken.

However, the ministry this week said it would begin an inquiry into the vessels' dumping of fish and the decision not to prosecute.

Environmental organisation WWF said the inquiry should be widened to review the deaths of the Hector's dolphins.

"If the Ministry knows about dolphin deaths that are caught on camera and is still not reporting these, then what happens when endangered Hector's and Maui dolphins die in fishing nets off camera?" spokesman Peter Hardstaff said.