Nine Hector's dolphins have been found dead around the South Island in the past four months.
A Hector's Dolphin (File photo) Photo: RNZ / Supplied
Seven of the dead dolphins were calves, and the most recent discovery was a Hector's dolphin with its tail end missing at a beach near Mikonui, south of Hokitika, last week.
Hector's dolphins are the world's smallest dolphin species, with adults measuring about 1.5m long.
Department of Conservation (DOC) aquatic director Elizabeth Heeg said the adult dolphin appeared to have died recently. It was too early to say what had caused its death but there was some evidence of shark bite.
It was collected by DOC staff and frozen so it could be sent to Massey University to be necropsied.
A very decomposed and scavenged Māui dolphin was also found at Muriwai on Christmas Day but was not collected. Six of the dolphins found were frozen and sent to Massey University.
"They are gradually being thawed and examined by the pathologist. We've received results from necropsies on two calves, but a definite diagnosis wasn't possible due to decomposition levels."
Heeg said maternal separation was cited as the possible cause of death of those two calves.
"Young calves can die when they are separated from their mothers, for example during storm conditions. This can be considered as a potential cause of death for all young calves but there is no reliable way of confirming this diagnosis."
The other dolphins collected since November are still under investigation.
Identifiable through their distinctive round dorsal fins, Hector's dolphins' bodies are grey with black and white markings.
The population is estimated to be about 15,000 and they are classified as Nationally Vulnerable in the National Threat Classification System.
Heeg said the information from necropsies helped with future planning for marine protection of Hector's and Māui dolphins.
She thanked the member of the public who reported the find as it meant DOC could obtain better information about the animal.
"We urge anyone finding a dead Hector's or Māui dolphin to report it to DOC via 0800 DOC HOT. It is also important for the public to report live sightings via the DOC webpage, or the hotline."