Almost 240 pilot whales have died after being stranded on a remote New Zealand island. The marine mammals got lost on Pitt Island in the South Pacific on Monday, more than 800 kilometers from the east coast of New Zealand, the country’s conservation authority said on Wednesday. Around 240 pilot whales died on neighboring Chatham Island on Saturday.

Some of the whales were dead when they arrived, but the rest needed to be euthanized to minimize suffering, said Dave Lundquist, an adviser to the agency. In the region, rescuers would not actively return the marine mammals to the water “because of the risk of shark attacks on humans and the whales themselves, so euthanasia was the most humane solution.” Pitt Island is New Zealand’s most remote inhabited island, with limited communications and difficult logistics, according to the agency.

According to the whale protection organization Project Jonah, with a total of almost 480 dead whales within a few days, these were major strandings in the Pacific state. “While there are large mass strandings at Farewell Spit (on the northern tip of New Zealand’s South Island), there are an average of 70 to 80 whales.”

Communication Conservation Agency Facebook post Project Jonah