Why did 12 sperm whales end up on German and Dutch beaches last week? What caused them to die? An autopsy of the more than 10-meter-long (33-foot-long) carcasses is supposed to reveal answers.

For the autopsy, the whales were transported from the beach to mainland Germany. "Difficult and fascinating at the same time," Almut Kottwitz - the deputy environment minister of the German state of Lower Saxony - told DW. A female sperm whale weighs 15 metric tons (16.5 tons), a male up to 60 tonnes. Even though the beached whales were still quite young, they had to be moved with cranes.

First, the whale's skin is cut into strips and peeled from the body. Preparers removed its muscles and ligaments, and gathered up the innards. "It cut me to the quick to see how these beautiful animals were being skinned and torn apart," an observer of the procedure told DW.

One of the skeletons was brought to Giessen University. Visible here is the whale's jaw - the bones will be treated for display. Another skeleton will be exhibited at a marine museum in Stralsund.

Some of the beached whales seem to have been undernourished, the atopsies found. No wonder: sperm whales feed on giant squids. And these don't live in the North Sea. "Their stomachs and their bowels were entirely empty," Almut Kottwitz told DW, adding that undernourishment seems to be "at least one of the reasons why they died." When whales are hungry and weak, they can get more easily lost.

Others among the sperm whales, however, seem to have been well-fed before they ended up on the beach, Ursula Siebert of the University of Veterinary Medicine in Hannover told DW: "They still had undigested beaks of giant squids in their stomachs, and feces in their bowels." Once on the beach, their weight compresses their blood vessels and lungs, causing them to die.

Sperm whales are not made to live in the shallow North Sea. They mostly live thousands of meters under water. In the North Sea, their echolocation doesn't work correctly. "When they arrive at the North Sea, they don't have muchof a chance of finding their way out of it again," vet and zoologist Siebert said. Ultimately, they beach and die.

A week ago, more than 80 short-finned pilot whales got stranded on the beach of the Indian state of Tamil Nadu. Conservationists managed to push some animals back into the sea, but most of them died. Fabian Ritter of the Whale and Dolphin Conservation estimates that thousands of whales beach every year.

The more socially minded a whale species is, the higher the number of whales that beach from that group. The long-finned pilot whale is one of these species, Fabian Ritter says. These whales have a very strong connection within their family group, or pod. "When the leader is ill or out of sorts, and swims onto the beach, the other group members follow - out of loyalty."

Conservationists warn that underwater noise is dangerous for marine mammals. "Whales have a very sensitive sense of hearing and communicate via sound with each other," Fabian Ritter says. "Loud noise such as from military exercises disorients them." Especially beaked whales are known to beach more often when there is too much noise underwater, Rittter says.

Solar winds disturb the Earth's magnetic field. Whales might get confused and beach more frequently, researchers found. At the end of December 2015 were three major solar winds, physicist Klaus Vanselow of Kiel University told DW. This might have led the 12 sperm whales to take a wrong turn into the North Sea - and end in death on its beaches.