A new analysis by Prof Slooten and an Otago University marine scientist, Associate Prof Steve Dawson, showed the number of Hector's dolphins caught in commercial gill nets was more than 10 times higher than sustainable levels, the two scientists said.
The study used the Potential Biological Removal method, developed by the United States National Marine Fisheries Service and commonly used for determining a level of human impact on marine mammals which, if exceeded, was likely to cause population decline.
Prof Slooten said the latest dolphin figures were "shocking" but were also consistent with population viability analyses carried out by scientists from Niwa, the fishing industry and Otago University.
The World Conservation Union has classified Hector's dolphins - which are found only in New Zealand waters - as endangered, and Maui's dolphins, which are also endemic, as "critically endangered".
The latter category was "the last step before extinction", Prof Slooten said.
"They are waving the biggest possible red flag for Maui's dolphins and the next biggest for Hector's dolphins," she said.
About 7500 Hector's dolphins remain, but only about 100 Maui's dolphins survive, the latter on the North Island's west coast. Niwa estimated 110-150 Hector's dolphins were killed each year from 2000 to 2006.
Unless more protective action was taken, New Zealand could be viewed internationally as failing to pursue sustainable fishing practices and not "walking the talk" about its "clean green" image, she said.
In May, Fisheries Minister Jim Anderton announced new protection measures, which were to have been enacted on October 1. These measures, arising from a two-year consultation period, were likely to slow population declines rather than halt them.
However, the fishing industry had taken the minister to court before the October 1 deadline, resulting in dolphin protection being delayed again, she said.
The main threat to the dolphins was entanglement in fishing gear, particularly gill nets. Switching to more selective, sustainable fishing methods would provide better protection, she said.
