Two more rare Hector's dolphins have been found dead on South Island beaches, with 14 total found deceased in the past five months, DOC says.
One dolphin was discovered dead at Tiwai on Saturday and another was found on a beach south of Greymouth last Monday.
In a statement, Department of Conservation marine species manager Katie Clemens-Seely said it remained a mystery why so many of the dolphins had been found dead.
“Sadly, this makes 14 Hector’s dolphins found dead around the South Island since early November 2021," she said.
“At this stage, we don’t know why we’ve had this many Hector’s dolphins wash up over the past four months. We’re waiting for the remaining necropsy results to understand more about possible causes of death.”
Twelve of the dolphins have been sent to Massey University for examination, DOC said. Eight of the recent deaths are said to have been calves.
“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."
When deceased dolphins are reported and retrieved quickly, they can be chilled and sent to a pathologist.
The adult dolphin found at Greymouth had been very decomposed with only a spine and tail remaining when discovered.
DOC said it presumed the remains were washed out to sea as they could later not locate them. It said it would be impossible to determine its cause of death.
The Tiwai dolphin appeared to be an adult and has been sent to Massey University for examination.
“The information from the necropsies will help us build our understanding of Hector’s and Māui dolphins and help with future planning for marine protection and management," Clemens-Seely said.
“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."
A very decomposed and scavenged Māui dolphin was also found at Muriwai, west of Auckland, on Christmas Day but was not collected. Māui’s dolphins are a critically endangered subspecies of the Hector's dolphin.
DOC said age-related disease has been cited as the probable cause of death of an adult female dolphin found near Hokitika in late November.
Meanwhile, the other dolphins collected since November are still under investigation.
According to the World Wildlife Fund, Hector’s dolphins are the "smallest and rarest marine dolphins in the world".