Pilot whales, 145 of them, that washed ashore on a southern New Zealand beach have died. Many were euthanized by conservation workers.

A hiker discovered the beached whales stranded ashore Saturday on Stewart Island, a remote island with a population of about 375 people. About 75 of the whales along Mason Bay were dead at the time.

Conservation workers believed the whales were beached a day before they were found, as they were partially buried in sand and in poor health. They euthanized the remaining whales, saying they couldn't be saved.

“Sadly, the likelihood of being able to successfully re-float the remaining whales was extremely low," Ren Leppens, the Department of Conservation's operations manager for the island, said in a statement. "The remote location, lack of nearby personnel and the whales’ deteriorating condition meant the most humane thing to do was to euthanize.”

Leppens told The New York Times that the beach has had three previous mass strandings — in 1998, over 300 whales beached near Mason Bay.

On Sunday at the northern end of the country, 10 pygmy killer whales were found washed ashore at Ninety Mile Beach. Two have died and conservation workers are trying to save the other eight by floating them from a different beach on the East Coast.

It's unclear what caused either stranding. 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.

Marine mammal strandings are common along New Zealand shores, as the Department of Conservation reports responding to about 85 incidents, some for single animals, annually.

Contributing: The Associated Press. Follow Ashley May on Twitter: @AshleyMayTweets