Australian rescuers were hoping to save 20 more pilot whales stranded off the coast of the island of Tasmania on Thursday after 70 were successfully returned to the ocean.
"We are confident most of those animals have got away,” Kris Carlyon, a wildlife biologist with Australia's Marine Conservation Program, told a press conference Thursday.
Tasmania's largest mass stranding has seen 470 whales trapped on a sandbank on the island's west coast this week. While the final rescue efforts are underway, crews are also left to remove the carcasses of 380 whales that died.
The bodies will be disposed of at sea, preferably, over the coming days before they bloat and float into the tides, Nic Deka, regional manager for Tasmania's Parks and Wildlife Service, said.
“They will present a significant navigation hazard if we don’t contain them,” Deka said.
The pod of an estimated 270 whales stuck on a sandbank was first detected Monday. Another 200 whales were found Wednesday about six miles down the coast.
Once beached, the whales only have a matter of days to survive because their organs — no longer suspended by water — are damaged.
The cause of the mass stranding has yet to be determined.
The event is not uncommon and strandings twice as large have been recorded in New Zealand, Carlyon has said. But the current stranding has set a new record for Australia, with the country's last record set in 1996 with 320 pilot whales stuck at the town of Dunsborough.
“There is little we can do to prevent this occurring in the future," Carlyon said earlier this week.
Download the NBC News app for breaking news and politics
Pilot whales have strong social ties and even if only a few members of a pod veer off course, the others often follow. It makes rebeaching a possibility, as the animals rescued try to reconnect with the rest of the pod.
But Carlyon said as of Thursday, none of the whales that have been rescued — that were tagged in order to be identifiable — have returned to the coastline where the carcasses have piled up.
Four whales that are alive but weakened and suffering as a result of the stranding will have to be euthanized, Carlyon said.
“These are animals that we have given a chance, we tried to release them and they haven’t done well," he said. "We don’t believe trying to release them again is a viable option."
The Associated Press contributed to this report.