Sea Shepherd are calling on the Trump administration to stop buying New Zealand snapper due to the bycatch deaths of critically-endangered Māui dolphins.

A Māui (Hector's) dolphin, dead in a net. Source: Supplied

The organisation says the US has a law - the Marine Mammal Protection Act - prohibiting it from importing seafood from countries which fail to prevent the bycatch of endangered species in line with US standards.

"There is no question that New Zealand fails to meet such standards in the case of the Māui dolphin," Sea Shepherd said in a release, adding that "the current bycatch of Māui dolphins is estimated to be two to four individuals per year".

The organisation says the US is failing to enforce its law, and has continued to import between 25 and 50 tonnes of New Zealand snapper per month.

"The snapper fishery is known to use gear that ensnares Māui dolphins – and this is just one fishery among many that incidentally captures Māui dolphins," the release read.

Sea Shepherd New Zealand Director Michael Lawry said there is already a precedent case of using the MMPA to halt importation.

In 2017, three US organisations petitioned a federal judge, asking for a ban on gillnet-harvested seafood from the Gulf of California due to the impact there on the population of vaquita - a small, critically-endangered porpoise.

They were successful, and the judge in July last year ordered President Trump to comply.

Sea Shepherd's legal department says if the US does not comply in this case also, they will seek legal redress.

In petition documents obtained by 1 NEWS, Sea Shepherd gives the US government a deadline of 60 days from February 6 to take action.

The petition says "gillnet and trawl fisheries on the West Coast of New Zealand’s North Island do not meet US standards, and emergency rulemaking is required to ban imports.

"In the case of the Māui dolphin, it is clear that New Zealand export fisheries using gillnets and trawls are exceeding the bycatch limit.

"By an overwhelming margin, the weight of the evidence proves that New Zealand’s failure to manage bycatch from gillnet and trawl fisheries is driving the Māui dolphin to extinction.

"In fact, without serious changes to fisheries management, the Māui dolphin will likely become the next vaquita — a cetacean whose hopes for survival are in serious question.

"US consumers are contributing to the Māui dolphin’s decline by purchasing imported products from fisheries associated with high levels of bycatch.

"Action is required — and it is required now."

Seafood New Zealand strongly refutes claims

Seafood New Zealand Chief Executive Tim Panckhurst strongly denied that Māui's dolphins are being caught, saying such claims put at risk a $2 billion export industry.

"Conservation measures for the prevention of Māui dolphin captures are working, with no sightings or captures of the dolphin in more than 2230 observer days since 2012," he said.

"The effectiveness of these measures has been verified by independent government observers on board fishing vessels in the Māui dolphins' known habitat range.

"The New Zealand seafood industry fully supports a range of significant fishing restrictions that have been in place and working since 2012.

"These include prohibitions on the use of set nets and trawls up to seven nautical miles throughout almost all of Māui known habitat range, between Maunganui Bluff and Hawera.

"Although the true population size of Maui remains open to conjecture, we acknowledge it is very small, and the New Zealand seafood industry fully supports their protection."

Seafood New Zealand 'the odd one out' in terms of opinion, scientist says

Marine mammal expert Professor Liz Slooten of Otago University's Department of Zoology said Seafood New Zealand's stance was not unexpected.

She said the numbers quoted by Sea Shepherd in terms of by-catch were the most accurate estimates possible, and were backed by most in the marine mammal scientific community.

"It's not just me - it was a team of experts who estimated that it was five per year prior to 2012, and then the bit that I did, I took that estimate and looked at what extensions for that protection have happened since 2012," Ms Slooten said.

"I've estimated in a paper ... that five dolphins per year have come down to 2-3.

"This is also consistent with the most recent science work and includes another person from the IWC scientific committee Justin Cook ... he's been estimating survival rates of Māui dolphins, and that's consistent - two individuals per year.

They are saying there has been no reported dolphins catches in that time - now the number of reported catches and the number of actual catches are usually wildly different.

"The reports either come from fishermen directly, or from observers, and Fisheries observers are carried on about two per cent of vessels - and fishermen themselves only report in the order of about one per cent of captures.

"So the number that get caught, only about 1-2 per cent of those get reported.

"Adding to that ... for Māui dolphins, there may only be about 57 individuals, and the chance of one of those being caught on an observed vessel are virtually nil.

"What they will probably tell you is that off Taranaki the observer coverage is 98 per cent between two and seven nautical miles offshore - but if you look at the whole of Māui dolphin habitat, that comes down to less than 15 per cent.

"So you can sort of play the numbers and make it sound like the observer coverage is quite high - but only for a very specific area, and only for larger boats.

"This is what they've been doing for the last several decades ... so that's exactly what I would have expected them to do."