Hundreds of whales died overnight on a beach in New Zealand’s South Island after they got stranded there on Thursday. The Department of Conservation found that more than 70% of the 416 pilot whales that beached themselves at Farewell Spit, Golden Bay, had died by early Friday morning. Authorities believe this is the largest such stranding in decades, The Guardian reported.

Officials have “no clue” why the whales had beached themselves, the department’s regional team leader Andrew Lamason said. However, researchers believe that cetaceans usually beach themselves when they no longer have the energy to stay afloat, or are old and sick, and sometimes wait for the tide to bring them ashore.

Volunteers pour water onto some of the hundreds of stranded pilot whales still alive after one of the country's largest recorded mass whale strandings, in Golden Bay, at the top of New Zealand's South Island. Pic: Anthony Phelps/Reuters)

Authorities appealed to local residents to head to the beach to help save the remaining 100 whales. They were asked to bring towels, buckets and sheets to keep the aquatic animals cool, calm and wet. “It is one of the saddest things I have seen, that many sentient creatures just wasted on the beach,” Peter Wiles, one of the first volunteers to reach the spot, told Fairfax New Zealand.

Another volunteer Ana Wiles told BBC, “One of the nicest things was we managed to float off a couple [of whales], and they had babies and the babies were following.” Project Jonah, a marine mammal charity in New Zealand, is leading the efforts to save the whales.

Volunteers had been able to re-float the 100 remaining whales around 10.30 am (local time), but 90 of them had beached themselves again during low tide in the afternoon. DOC members and some 500 volunteers are now trying to keep the surviving whales healthy till the next high tide at lunchtime on Saturday.

Lamason explained that it was common for whales part of a mass stranding to re-beach themselves to try and stay close to their pod, most of which had died ashore. “Unless they get a couple of strong leaders who decide to head out to sea, the remaining whales will try and keep with their pod on the beach,” he said, adding that whale strandings were common in Golden Bay.

This is the third largest whale stranding in the history of New Zealand. A thousand whales had beached on the Chatham Islands in 1918, and 450 had beached themselves at the Great Barrier Island off the coast of Auckland in 1985.