Late Tuesday afternoon, 31 of the whales beached at an Audobon Society sanctuary on the Wellfleet/Eastham line, despite efforts by volunteers in boats trying to herd the small, black whales back out to the sea.

Earlier in the day, rescuers worked feverishly to free the same pod from another location, Lieutenant's Island in Wellfleet. They were mostly successful at that location, shepherding 31 back out to sea, although 14 were either euthanized or died of shock.

But when the entire pod restranded near Sunken Meadow Beach late in the day, in a marshy, hard-to-access location with dark approaching, marine scientists were forced to make the decision none wanted to make, said New England Aquarium spokesman Tony LaCasse.

"After two days of trying to give these animals any opportunity we could, a decision was made by the veteranians on site to euthanize those animals that weren't already dead," he said. "It's probably one of the harder decisions that anyone can make."

Fifty-six of the sociable marine mammals have either died or been euthanized on Cape Cod in the past two days.

On Monday, vacationers and volunteers worked feverishly to push the whales to deeper seas after they beached at Chapin Beach in Dennis. Eleven died Monday -- 9 at Chapin Beach, one was euthanized later in Sandwich, and still another beached and died in Yarmouth.

"It really is the worst case scenario," said Christopher Bailey of the International Fund for Animal Welfare.

Despite Monday's efforts, 45 of the animals beached again around 4 a.m. Tuesday at Lieutenant Island.

About 300 people came to the area to try to help the whales Tuesday morning. 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.

Some of the whales thrashed in the shallow water, while others wailed back and forth to each other.

"It's heartbreaking," Bailey said.

Rescuers were largely successful there, eventually easing 31 blistered and sunburned whales out to sea.

Yet despite efforts to keep them in the water and turn them toward the open ocean, they swam ashore again, and this time there was nothing rescuers could do, LaCasse said. Twenty-five were euthanized and the rest died.

It was not immediately known why the whales became stranded. Bailey said the blood samples may help determine the cause of the stranding.

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.