Ten sperm whales that had beached themselves in the Aceh Province of Indonesia were spotted early Monday. Professional rescue teams and local volunteers worked into the night and were able to release six of them. The remaining four died.

Officials still don't know what caused the whales to strand themselves.

Conservation groups sent a team of at least 50 into the water to try and save the whales with the help of people nearby who were willing to lend a hand.

"Some people got injured on the coral and the high tide was also an obstacle but we tried our best," Sapto Aji Prabowo, head of the Aceh conservation agency, told Reuters.

The teams released seven of the whales in the morning but one washed back to shore after dying, The Jakarta Post reports. They used boats, ropes and tarps to free the whales from the shallows and tow them back to the open ocean.

Officials say injury and exhaustion led to the four whale deaths. Scientists will continue to monitor the survivors using drones to ensure they don't wash back to shore, risking death or further injury.

World Wildlife Fund Indonesia official Aryo Tjiptohandono told the Postthat keeping crowds under control is essential during rescues. The stress of seeing masses of people, Tjiptohandono said, can negatively affect whale health.

The challenge now is to bury the corpses of the dead whales before they bloat. Gases inside the whales can cause their bodies to explode, which could spread disease. The World Wildlife Fund of Indonesia tweeted that they will perform autopsies to try and find out what caused the beaching.

Beachings are uncommon in Indonesia. But in the archipelagian nation of more than 17,000 islands, it's not unheard of. A group of 29 pilot whales were stranded in 2016 on the eastern shore of Java — the island where the capital city, Jakarta, is located.

The U.S. Fish and Wildlife Service lists sperm whales as endangered species. Before worldwide whaling practices decreased the population, it stood at about 1.1 million. Now it's an estimated 360,000, according to the American Cetacean Society. Sperm whales live in every ocean and the Mediterranean Sea. Adult males can reach almost 60 feet in length and weigh up to 45 tons. They're the largest of the toothed whales, and are most famously portrayed in Herman Melville's Moby Dick.

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