Doc was alerted to the stranded whales at 10.30pm on Saturday by a tramper camping in the area. About 75 were already dead and conservation workers chose to euthanize the others due to their poor condition and remote location.
Across a period of several days a year ago, more than 650 pilot whales beached themselves on a thin strip of land projecting off New Zealand's South Island. They chose to euthanize the remaining stranded whales because of the difficulty of accessing the remote location.
Marine mammal charity Project Jonah received a call from a member of the public on Sunday night saying whales were stranded on Ninety Mile Beach.
"However, it's always a heart-breaking decision to make", he said.
A walker discovered the carcasses lining the shore at Mason Bay on the island, 60km south of Invercargill, on Saturday, The New Zealand Herald reported.
DOC has notified local iwi Ngāi Tahu and is working together on next steps. In fact, most strandings remain a mystery but wildlife experts say sickness, falling tide, extreme weather and being chased by a predator could contribute to beaching whales.
A mass sighting like this is rare, the DOC said.More news: Hamilton clinches pole at Abu Dhabi GP
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Conservation workers said they were left with no choice but to euthanise half of the whales as the chance of rehabilitating them was "extremely low".
The DOC said in a statement that whale strandings are not uncommon in New Zealand and that there are about 85 incidents a year.
Hupman said not a lot was known about why whales stranded, but they were usually coming onto the beach for a reason.
The largest is thought to have taken place in 1918, when approximately 1,000 whales stranded themselves on Chatham Islands.
Pilot whales are one of the most populous whale species. Two have since died and re-float attempts will be made tomorrow.
In separate incidents, 12 pygmy whales and a sperm whale also beached in New Zealand over the weekend.
Pilot whales at Mason Bay, Rakiura on Stewart Island, New Zealand, Nov. 25, 2018.