Wellington, New Zealand ? A dozen sperm whales that died after beaching themselves on the west coast of New Zealand’s North Island were buried early today, conservation officials said.

The whales, each weighing about 13 tons, died after becoming stranded Friday on the remote beach west of Auckland.

“Refloating was just not an option due to the sheer size of the whales — it was an impossibility,” said Conservation Department spokesman Warwick Murray.

Sperm whales are the world’s largest toothed whales. Adults can grow to up to 59 feet and weigh more than 27.5 tons.

“Such huge whales are often crushed by their own weight when they are out of the water,” Murray said.

Conservation officials said bulldozers today were being used to bury the whales.

Marine mammal experts were trying to determine why the pod of mainly females had gone ashore in the area, not normally a site of strandings.

Biopsies and measurements of the carcasses had been taken and sent for testing, Murray said, adding it was possible a couple of the whales had been ill.

Experts don’t know why whales beach themselves.

One of a dozen sperm whales lies stranded and dead between Karekare and Whatipu beaches west of Auckland. Workers began burying the dead whales early today.

Mass strandings of pilot whales are relatively common around parts of New Zealand’s coastline, but Murray said beachings of large groups of sperm whales were very rare.

Auckland, New Zealand’s main commercial center, is 419 miles north of the capital, Wellington.