Fifty-six of the pilot whales have died, including 31 that officials say had to be euthanized.
More than 40 of the whales stranded themselves today, for the second time in two days.
Volunteers were able to push most of the whales back out to sea yesterday, but most of the marine mammals were too tired or shocked for a similar rescue today.
Chris Bailey of the International Fund for Animal Welfare called today's scene "heartbreaking." Some of the creatures were thrashing in the shallow water and wailing to each other.
Pilot whales are highly social animals, but experts aren't sure why they occasionally become stranded in large groups
"People say it's part of nature and to an extent it is. But still it's frustrating to see such smart animals up on the beach ... unable to do anything," veterinarian Scott Weber told CBS News Correspondent Richard Schlesinger.
The mass stranding at Sunken Meadow Beach on the Wellfleet/Eastham line comes a day after vacationers and volunteers worked feverishly to push the original group of 56 pilot whales out to deeper seas after they beached about 25 miles away at Chapin Beach in Dennis. Nine died Monday.
"It really is the worst case scenario," said Christopher Bailey of the International Fund for Animal Welfare.
On Tuesday morning, five to six of the whales were euthanized after scientists determined they couldn't survive, said Tony Lacasse, spokesman for the New England Aquarium. Others swam back out to sea with some guidance from rescuers after being put on their stomachs so they wouldn't suffocate, he said.
Even those strong enough to swim to sea had a slim chance of survival after suffering shock, sunburn and blisters, Frady said.
"They're just not in good condition," she said.
The whales beached for the second time Tuesday in Eastham west of Sunken Meadow, Frady said.
Pilot whales are highly social animals that travel and feed in groups. The deaths from the strandings Monday and Tuesday would devastate the small group, Lacasse said.
About 300 people came to a remote area near Lieutenant Island to try to help the whales Tuesday morning. However, about half left when workers tried to restrict the scene to marine professionals and the media.
Some of the whales thrashed in the shallow water, while others wailed back and forth to each other.
"It's heartbreaking," Bailey said.
Earlier in the day, volunteers put blankets and bedsheets on the whales to regulate their body temperature, while schoolchildren filled buckets of water to pour on the animals to keep them comfortable, Bailey said.
It was not immediately known why the whales became stranded. Bailey said the blood samples may help determine the cause of the stranding.
Another pilot whale died on a beach Monday night, in the Cape Cod town of Sandwich about 15 miles to the west. That whale was euthanized so as not to lead others astray. A second lone whale beached in Yarmouth on Monday night, Frady said.
A necropsy was scheduled for the first whale that died to try to determine why they became stranded.
Pilot whales range from 12 to 16 feet in length as adults and weigh about 1,800 pounds. Also known as blackfish for their color, they feed on squid, sand eels and small crustaceans.
In July 2000, 10 pilot whales died after stranding in shallow water off Nantucket Island, and on Christmas Eve of 1991, 31 stranded pilot whales died off Cape Cod.