DOC's Marine Technical Advisor Kristina Hillock says the baby dolphin – thought to be just a few days old - was found on Karioitahi Beach, west of Pukekohe, on Wednesday 20 December.
The animal's gender and exact age are unknown.
"Details are very sparse at this point in time," Kristina says.
"The discovery of the animal was reported to DOC and our local team and iwi representatives responded as soon as practical to retrieve it."
It has been sent for necropsy at Massey University, the results of which are expected in late January or early February.
"We're keen to understand more about this animal, but we need some robust science undertaken. The cause of death is unknown and any other commentary would be speculation and that would be unhelpful.
"We'll have more information next year, and may then be able to offer details on what caused the dolphin's death.
Kristina Hillock reiterated DOC's call to the public to report any dead Māui or Hector's dolphins as soon as possible, as this gives the best opportunity for valuable necropsy and science to be carried out to learn more about the dolphins.
"If you see dolphins this summer, think 'rounded fin – send it in!"
Report Māui or Hector's dolphin sightings anywhere in New Zealand to our hotline
- 0800 DOC HOT (0800 362 468).
DOC also has an online reporting form on its website, including a portal to upload pictures or video.
Background information
The Māui dolphins are one of the smallest and rarest dolphin species in the world. They are only found off the west coast of New Zealand's North Island, in a range from south Taranaki to Auckland. Their conservation classification is "nationally critical" and they face threats from fishing, human activities such as gas and oil exploration, and toxoplasmosis.
They are identifiable by their rounded dorsal fin, which is often likened to the shape a Mickey Mouse ear.
