Maui's dolphins, the world's rarest dolphin species that lives only in waters off the coast of New Zealand, could disappear within 15 years unless protection efforts are launched to pull it back from the brink of extinction, conservationists say.

Researchers at German conservation group NABU, in what they're characterizing as a "loud wake-up call," report that less than 50 of the small, 5-foot-long dolphins remain in the wild, with just 10 to 12 mature females who might give birth to new offspring.

The numbers represent a 97 percent drop from the population that existed in the 1970s, experts say.

If the species is to survive, NABU says, measures to keep them from dying in fishing nets should be expanded, and a complete ban on fishing across its entire habitat should be considered.

"These new figures are a loud wake-up call: New Zealand has to abandon its current stance, which places the interests of the fishing industry above biodiversity conservation, and finally protect the dolphins' habitat from harmful fishing nets, seismic airgun blasts and oil and gas extraction," said Barbara Maas, head of endangered species conservation for NABU.

Unless such measures are put in place, the extinction of the Maui's dolphins is a "matter of when, not if," she said.

The rare dolphins, known scientifically as Cephalorhynchus hectori maui, are a subspecies of the Hector's dolphin, found only in shallow coastal waters off the western side of the country's North Island.

Another subspecies that inhabits waters off South Island is more abundant, experts say.

Maui's dolphins average between 4 feet and 5 feet in length and seldom weigh much more than 100 pounds. Females have a low reproductive rate - just one calf every 2 to 4 years - making it difficult for the species to recover from losses due to human activity.

The main threat to Maui's dolphins is fishing that uses gillnets or trawling, say the researchers who estimate five of the marine mammals are killed each year.

Maui's dolphin was listed as critically endangered by the International Union for Conservation of Nature in 2013.

Although New Zealand has placed some restrictions on gillnets, drift nets, and trawling, in certain areas of the dolphin's habitat, conservationists have said the measure do not go far enough to ensure the survival of the species.

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