The World Wildlife Fund said that Maui's dolphins, which are found only along North Island's west coast and are on the brink of extinction, urgently need protection from set nets and trawler nets if they are to survive.
Official estimates are that just 111 Maui's dolphins still live in the wild.
Set nets are used by recreational fishers near the coastline, while large trawl nets are used further out to sea in commercial fishing to catch large schools of fish.
The numbers for another endangered New Zealand species, the Hector's dolphin, have declined from an estimated 29,000 in the 1970s to 7,000 currently.
Photographs of 22 common dolphins killed in trawler nets off North Island's west coast last December - released by the government Tuesday - were proof that current fishing controls are failing to protect endangered dolphins, said Chris Howe, the executive director of the WWF's New Zealand branch.
The deaths showed that the fishing industry cannot be trusted to follow the voluntary code of practice that currently protects the species, he said. The government-imposed code was set up to minimize accidental capture of dolphins during trawl fishing.
"All fishing with set nets and trawl nets should be banned throughout the range of Hector's and Maui's dolphins," Howe told The Associated Press.
"That's the only way to ensure a slow-breeding, rare species can recover," he said.
Conservation Minister Steve Chadwick said she was "not surprised" that conservation groups are calling for nets to be withdrawn.
"We'll have to consider how realistic that is while we also have sustainable fishing and how we will manage protection of those endangered species," she told the AP.
Owen Symmans, chief executive of the New Zealand Seafood Industry Council, said the "accidental capture" of 22 dolphins was regrettable.
"Nobody wants to catch dolphins, common or otherwise, and fishermen ... feel gutted about this sort of thing," he said. "It's the last thing that they want in their nets."
He said trawlers move away "as soon as dolphin are seen," and the industry is committed to trying to avoid such events.
The government is due to release options for ways to further protect Maui's and Hector's dolphins, part of its response to conservation groups' demands.
About 214 international environmental and animal protection bodies urged New Zealand in a letter Wednesday to give "full protection" to the endangered Hector's and Maui's dolphins to prevent their extinction.
"Maui's dolphins, the world's smallest dolphin, are one of the rarest animals on earth and Hector's dolphins are almost as scarce as tigers," Care for the Wild International's Chief Executive Barbara Maas wrote in the letter.
Conservationists already have warned that even the best of the proposals will give the endangered dolphins only a 50-50 chance of recovering to their original numbers by 2050.
While many fishing boats obeyed the voluntary code of practice, it only took one or two who did not to wipe out the fragile species, Howe said.