Two more Hector's dolphins have been found dead on South Island beaches.
A Hector's dolphin. File photo Photo: Supplied
One was found south of Greymouth on 11 April, and another at Tiwai on 16 April.
Department of Conservation marine species manager Katie Clemens-Seely said 14 Hector's dolphins have been found dead around the South Island since last November. Eight of the recent deaths were calves.
It remains unknown why so many dolphins have died.
Clemens-Seely said the number of Hector's dolphin deaths fluctuated each year, but DOC had not been able to ascertain a particular pattern or trend over the years.
"It does seem as though there have been more dead Hector's dolphins discovered in recent months than for the same period last year for example, however, we do tend to see higher numbers of dead dolphins throughout the warmer months as compared to the colder months of the year."
The adult dolphin found at Greymouth was very decomposed with only the spine and tail remaining when it was discovered. It would be impossible to say what caused its death.
By the time DOC was alerted to the dead dolphin the remains could not be found - presumably they had been washed back out to sea.
The Tiwai dolphin also appeared to be an adult and has been collected by DOC staff to send to Massey University for examination.
When deceased dolphins are reported and retrieved quickly they can be chilled and sent to the pathologist.
Twelve of the dolphins have been sent to Massey University but staff shortages due to Covid-19 have delayed some of the results.
"They are gradually being examined by the pathologist. We've received results from necropsies on four calves, but a definite diagnosis wasn't possible due to decomposition," Clemens-Seely said.
"Maternal separation, potentially during storm conditions, has been cited as the possible cause of death of those four calves."
There are two stages to a necropsy: an examination of the organs and tissues and histological analysis done via microscope, which can identify disease.
"Due to staff shortages from Covid there's been some delays on the histology component of the necropsy, so this has delayed us getting the final results and therefore delayed the reports for several of the dolphins."
DOC is waiting for the remaining necropsy results to understand more about possible causes of death.
Results from an adult female Hector's dolphin found near Hokitika on 28 November found age-related disease was the probable cause of death.
"The death of any marine mammal is very sad, but it is also a fact of nature. The Hector's dolphin is classified as nationally vulnerable and there are approximately 15,000, mainly located around the South Island of New Zealand, Clemens-Seeley said.
The other dolphins collected since November are still under investigation and results will be shared on the DOC website when available.
Anyone who sees Hector's or Māui dolphins or finds them dead is being asked to report it to DOC by calling 0800 DOC HOT.