Australian wildlife officers have euthanized 90 false killer whales stranded on a remote beach in Tasmania, after rough ocean conditions made rescue efforts impossible.

More than 150 whales were found stranded near the Arthur River on the island’s west coast late Tuesday, according to Tasmania’s Department of Natural Resources and Environment. By Wednesday morning, only 90 were still alive. Attempts to refloat two whales failed, as strong winds and rough seas forced them back to shore.

“It’s quite rough, and the animals just can’t get past the break to get out. They just keep turning around and coming back towards the beach,” said Shelley Graham, incident controller with Tasmania Parks & Wildlife Service.

Aerial images showed the whales scattered along the beach, some half-buried in sand and others trapped in shallow waters. Given their distress and deteriorating condition, authorities decided to euthanize them to minimize suffering.

Tasmania last saw such a large false killer whale stranding in 1974, when 160 to 170 whales were beached on the northern coast. The cause of mass strandings remains uncertain, with scientists citing factors such as illness, disorientation, weather, and magnetic anomalies.