Marine biologists believe there are only about 55 Maui's dolphins left, and they could be wiped out by 2030.
The president of the Society for Marine Mammalogy, an organization of 2,000 scientists in 60 countries, has written to New Zealand Prime Minister John Key urging immediate action, China's Xinhua news agency reported Thursday.
In the letter, SMM President Helene Marsh said fishing nets annually kill about 9 percent of Maui's dolphins over 1 year old.
"Scientific advice often involves a degree of uncertainty, but in a situation such as this one involving a critically endangered subspecies delay to resolve uncertainty could have dire, irrevocable results," she wrote. "I encourage you to act quickly and decisively to provide the leadership in marine conservation that the world expects of your country."
Barbara Maas of the Nature and Biodiversity Conservation Union, based in Germany, criticized New Zealand's refusal to prohibit the use of gill and trawl nets in coastal waters where Maui's dolphins live.
"With every passing day of inaction, Maui's dolphins are unnecessarily put at risk," she said in a statement. "The scientific evidence for an immediate zero tolerance approach to Maui's dolphin mortality is overwhelming."
The New Zealand government has argued there is no scientific evidence to support the assertion that a fishing ban would protect the Maui's dolphins.
The dolphins' name is taken from "te Ika a Maui," the Maori word for New Zealand's North Island.