Hector's dolphins are disappearing from South Island waters at an alarming rate, conservation campaigners Sea Shepherd say.
While there used to be more than 50,000 Hector's dolphins around New Zealand, the species was now only abundant along some South Island coastlines, the group said.
And with the exception of Banks Peninsula, near Christchurch, many sub-populations were dwindling to become critically endangered or possibly even "gone forever".
That included in areas such as Brighton and the Northern Catlins.
Sea Shepherd New Zealand's Grant Meikle said the group had recently been sailing across the south-east corner of the South Island monitoring and counting the numbers of Hector's dolphins, which are also known as pahu.
"(It's) very sad to see that some of them now have such low numbers," he said.
"Commercial trawling is still having an impact and if we are serious about saving some of the critical populations we need to remove this threat completely. We don't believe many of the deaths are being reported."
Sea Shepherd's Operation Pahu campaign aims to combine scientific research, with volunteer help and the monitoring of illegal fishing to help protect the dolphins.
It comes as Sea Shepherd announced last August it had pulled the plug on its decade-long mission to stop Japanese whalers in the Southern Ocean.
The group had sent ships to harass and hinder Japanese whalers for the past 12 years.
However, it said it couldn't match the economic and technological power of the whaling fleet after the Japanese military began monitoring its movements.