A marine mammal expert is casting doubt on a report that says a rare dolphin most likely died from blood poisoning.

The pathology report in to the death of what is believed to be a critically-endangered Māui dolphin, was released just over a week ago by the Department of Conservation.

It said a still-born foetus found inside the mammal most likely resulted in the mother developing blood poisoning.

But Otago University professor Liz Slooten said the report did not delve in to detail on whether the animal could have drowned in a fishing net, something she thought was a distinct possibility.

“We can’t be sure that it has been caught in a net but we can’t be sure that it has not. Only half of dolphins caught in gill nets have those kinds of markings so we can’t rule it out.”

Professor Slooten, who had carried out about 120 autopsies on dolphins, noted the mammal was healthy, indicating it had not been hungry or sick in the weeks leading up to its death.

She said Maui dolphins were teetering on the brink of extinction and wanted the government to implement the recommendations of the International Whaling Commission from three years ago.

This asked for fishing nets to be banned less than 20 nautical miles from shore from Northland to Whanagnui.

“It’s really sad in this case to have these two deaths because with this very small population of Maui dolphins of only about 55 individuals one year and older only half of those would be expected to be females, so that’s about 28…and half of those would be expected to be mature. So we are talking 14 breeding age females…so to lose one, especially one that was pregnant is really really bad.”

A Department of Conservation spokesperson said there were no signs the Gibson Beach dolphin was entangled in a net and this was not something it was looking at.