The International Whaling Commission has voiced its "grave concern" for the tiny Maui's dolphin and urged the Government to take further steps to protect the critically-endangered sub-species.

A New Zealand researcher who presented information to the IWC scientific committee, made up of a panel of 200 experts, is now warning numbers of the endemic dolphin could plummet to just between five to 10 individuals within 20 years if the Government did not improve its management of them.

Environmentalists have put their population at 55, while the NABU International Nature Conservation Foundation has recently claimed numbers have sunk to between 43 and 47 individuals, and the Department of Conservation estimates there are between 48 and 69.

The subspecies of Hector's dolphins are the world's smallest dolphins and are found in shallow coastal waters up to depths of 100 metres off the North Island's west coast.

In its just-released report, the committee requested New Zealand include harbours in protected areas, which should be extended further south to Whanganui and further offshore to 20 nautical miles.

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Within the recommended area, the IWC recommended set net fishing and trawling be banned.

Presently, the Government has in place a range of set net, trawling and drift net restrictions throughout the dolphins' habitat, while there are also restrictions on seabed mining and acoustic seismic survey work within the boundaries of the West Coast North Island Marine Mammal Sanctuary, which was extended in 2013 to include more of the Maui dolphin's range in the Taranaki area.

The Government was also reviewing a threat management plan already in place for the dolphins, with the programme to be informed by a marine research and advisory group of experts.

The IWC committee concluded that for the Maui dolphin, "the human-caused death of even one individual would increase the extinction risk" and the commission reiterated its previous recommendation that "highest priority should be assigned to immediate management actions to eliminate bycatch of Maui dolphins".

"The Committee again urges the New Zealand Government to commit to specific population increase targets and timelines, and again, respectfully requests that reports be provided annually on progress towards conservation goals," it reported.

Dr Liz Slooten of Otago University, who presented research to the committee at its recent meeting in San Diego, said the Government had so far ignored previous IWC recommendations of full protection, with just 19 per cent of the dolphins' habitat protected from gillnets and about five per cent protected from both gillnet and trawl fisheries.

Dr Slooten said the IWC had asked New Zealand to follow the lead of Mexico, which this year substantially increased its protection for vaquita, a rare species of porpoise, by increasing the protected area to seven times its previous size.

"Mexico is providing financial support for fishermen to make the transition to dolphin-safe fishing methods," Dr Slooten told the Herald from Holland.

"If we did this in New Zealand, this would turn dolphin protection into a win-win situation."

She said the extinction of the baiji or Yangtze River dolphin in China a few years ago had shocked the international science and conservation communities, and the IWC committee had now named the vaquita and the Maui's dolphin as the two top priorities.

Maui's dolphins have become a symbol for environmentalists challenging gill netting and trawling by commercial fishers, and Government oil and gas exploration block offers in habitat areas.

Earlier this year, Auckland councillors voted to oppose oil exploration in a sanctuary home to the dolphin, but stopped short of following Christchurch City Council and opposing any exploration, while a survey suggested Kiwis would be happy to pay for greater protection for the dolphins.