Māui dolphins. Photo: Department of Conservation / supplied
The Department of Conservation (DOC) is asking hardy winter beachgoers to report sightings of dead or stranded Māui dolphins washed up across Taranaki and the west coast of the North Island.
Marine science adviser Anton van Helden said although most sightings of critically endangered Māui were made in summer, DOC needed to increase the number year-round to overcome seasonal bias.
"We're trying to really understand the causes of deaths of the dolphins ... particularly trying to understand the problem which is the disease caused by the parasite Toxoplasma gondii."
The parasite was known to kill Māui by toxoplasmosis infection.
Early reporting of dead animals was needed to ensure carcasses could be collected and transported to Massey University in the best possible condition for necropsy, Van Helden said.
There are believed to be no more than 65 Māui dolphins left.
Māui dolphins. Photo: Department of Conservation / supplied
In addition to death, according to DOC's website, toxoplasmosis "is also known to cause behavioural changes, still births and reduced reproductive rates".
The dolphins catch it from cat faeces, the eggs (oocysts) potentially surviving for months and eventually ending up in the ocean via rainwater and wastewater.
"Unfortunately, toxoplasma oocysts cannot be treated by standard wastewater treatment methods, such as UV radiation," DOC's site says.
People can report sightings by calling 0800 DOC HOT (0800 362 468) or through the marine mammal sighting form.