A pod of about 40 beached pilot whales re-stranded themselves in New Zealand Tuesday after volunteers worked for hours to get them back into the sea, officials said.

The pod was part of a larger group of about 100 pilot whales which stranded at Golden Bay on the South Island on Monday, the Department of Conservation (DOC) said.

DOC spokesman Nigel Mountford said 34 of the original pod were confirmed dead and 26 were successfully refloated late Monday and had swum offshore.

He said hopes were fading for the remaining pilot whales, which swam back to shore after volunteers manoeuvred them into the water early Tuesday afternoon.

"It's disappointing, they just came back on shore," he said.

"They'll have to take their chances at high tide overnight. It's too dangerous for our volunteers to stay through the night, we're working right at the edge of our capability."

Mass strandings are common on the New Zealand coast and more than 50 pilot whales have died in two separate beachings in the same area in the past two months.

Pilot whales, which are members of the dolphin family and grow up to six metres (20 feet) long, are a common sight in New Zealand waters.

Scientists are unsure why pilot whales beach themselves, although they speculate it may occur when their sonar becomes scrambled in shallow water or when a sick member of the pod heads for shore and others follow.

Mass dolphin strandings at Cape Cod
New York (AFP) Jan 24, 2012 - At least 85 dolphins have beached themselves in a shallow inlet of a US nature reserve at Cape Cod, officials said Tuesday, adding that the cause of the mass strandings remained a mystery.

A spokesman for the International Fund for Animal Welfare said the huge number of beached mammals over the last two weeks, with most of them dying, was close to the amount usually recorded in the course of a year.

"We had a total of 85 confirmed strandings since January 12 and that number might be as high 101," AJ Cady said. "There are still about 16 dolphins reported in difficult locations we haven't been able to confirm."

"Of that number 35 were still alive. Fifty of them were dead by the time we reached them," Cady said.

The strandings took place in the area of Wellfleet and Eastham, which is notorious for sandbanks and twisting channels, just south of the famous hook of Cape Cod on the Atlantic coast of Massachusetts.

The area is the location of coastal and marine nature preserves and is famous for its population of endangered North Atlantic right whales and other sea life.

Cady said that the large number was "very unusual. In an average year we might handle a total of 120 dolphins over the course of the entire year and now we are almost at that number in a little over a week."

Cady said there were different theories why dolphins -- like their cousins the whales -- sometimes beach themselves in large numbers.

"One (theory) is that they just get lost. We're wondering if they were following food, a school of fish, and got trapped," he said.

"They are very sociable animals. They stay together as a group if one gets in trouble, you tend to see the whole family group get stranded at the same time because they try to stay together."