About 145 pilot whales died in New Zealand after being stranded during the weekend on Stewart Island in the extreme south of the country, officials said on Monday.

A hiker alerted authorities on Saturday night about the situation of the whales, who were stranded in Mason Bay in two separate groups about two kilometers apart, a Department of Conservation of New Zealand release said.

Half of the whales were dead when rescuers arrived and the condition of the rest, by the time they were found, was so bad it was decided to euthanise them, said Ren Leppens, operations manager at Rakiura.

"Sadly, the likelihood of being able to successfully re-float the remaining whales was extremely low. The remote location, lack of nearby personnel and the whales' deteriorating condition meant the most humane thing to do was to euthanise," said Leppens.

Pilot whales, also called long-finned pilot whale, are a specimen with a bulging forehead and a robust body that can reach between six and seven meters in length, Xinhua news agency reported.

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Marine mammals are frequently stranded on New Zealand's coasts and the average number of operations carried out by environmental officials is about 85 per year, most of them to save these animals individually.

The reasons why whales and dolphins can become stranded have not been clarified, although it is attributed to diseases, navigation errors, sudden changes in tides, being chased by predators or extreme weather conditions. (IANS)