"This is a joint decision for the ministers of conservation and fishing to make – but the Green Party still has a party view, which is that we want the strongest possible protection for these dolphins."
Maui dolphins are classified as "nationally critical", with only an estimated 63 individuals remaining, while the 15,000-strong Hector's dolphin population was considered "nationally vulnerable".
In July, Nash and Sage released a discussion document laying out options for a new threat management plan.
They included pushing out the boundaries of the West Coast North Island Marine Mammal Sanctuary south to Wellington - and for the Banks Peninsula Marine Mammal Sanctuary to extend north to Kaikōura, south to Timaru, and offshore to 20 nautical miles – with set netting and trawling banned in these areas.
The proposals also looked at how to deal with other threats facing the species, with options ranging from requiring a special code of conduct for seismic surveying in New Zealand's five marine mammal sanctuaries set up to protect Hector's and Māui dolphins,
to prohibiting any seismic surveys and seabed mining within the sanctuaries.
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Ardern's office referred questions about Hughes' letter to the ministers' offices.
A spokesperson for Nash declined to comment on Hughes' letter, but said the minister would respond to it.
Both ministers were still reviewing the response to consultation on the proposals, which ran for two months and drew more than 13,000 submissions.
Among them was a joint proposal by fishing giant Sanford and conservation group WWF New Zealand, which recommended smaller exclusion areas, and a bigger focus on education and scientific solutions, such as dolphin-spotting drones, to prevent bycatch.
Greenpeace hit out at that plan, arguing that it relied on complicated and unproven methods, and was at odds with the precautionary approach it said was needed to save the dolphins.
Industry group Seafood NZ has meanwhile claimed the Government proposals could put hundreds of small fishermen out of business and cost regional economies "hundreds of millions of dollars".
The group supported an "appropriate extension" of "scientifically-based" exclusion zones, along with the use of dolphin deterring technology, enhanced use of observers and the current camera trial.