Volunteers and rangers worked throughout Saturday to refloat around 25 of the animals at a beach on the Coromandel Peninsula. The creatures were part of a pod of around 40 pilot whales who got stranded earlier that day.
Five of the whales were discovered dead late on Saturday night at a site thought to be the original stranding location, the department said.
“Although the high tide at about 9pm on Saturday night had allowed the stranded whales to be refloated, members of the pod re-stranded this morning including several on rocky outcrops at the bay,” the department said in a statement on its Facebook account.
“Sadly, about a dozen have died after re-stranding on the rocks this morning. However, we are encouraged by the fact the majority of the stranded whales have re-joined the pod this morning and have been chaperoned out to deep water.”
The beach where the whales were found lies roughly 55km east of Auckland, the nation’s largest city.
Pilot whales, which can grow to above 6m in length, are a species prone to mass beaching. Just last month in Australia, more than 376 died in one event.
It was Australia’s largest mass stranding to date, with roughly 470 pilot whales stuck in a remote harbour on Tasmania’s rugged western seaboard.
As a species, the pilot whale is more akin to bottlenose dolphins than humpback whales, and they spend almost all of their time in the deep ocean feeding on squid and fish below 200m.
They form tight-knit groups, with some whales saying in the same pod for life. It is this tendency to form close bonds that can put the species at a disadvantage when they find themselves too close to the shore.
With additional reporting from agencies