Sperm whales are the largest of the world’s toothed whales—smaller than giant, filter-feeding blue whales, but still the size of four big elephants—and they live out in the deep ocean, where they feed on squid, along with the occasional octopus, ray, or shark. In Iceland, or western Norway, or around the Azores, places where the continental shelf drops off close to the coast, these whales sometimes swim into view of human civilization. Still, they’re rarely spotted at all and almost never in the sandy, tidal North Sea, a cul-de-sac of the Atlantic Ocean between the United Kingdom and Norway.
On a January afternoon in 2016, though, Dirk-Henner Lankenau, a biologist at the University of Heidelberg, was beachcombing on the German island of Wangerooge when two dark forms appeared in the distance. When he reached the shapes, Lankenau found that they were whales, stranded overnight on the shore and already dead. Four days later, another two sperm whales were seen floating, dead, off the coast of a nearby island. That same day five more were found marooned on the Dutch island of Texel. Another two washed up soon after. The next week another dead whale showed up on a British beach, with more to follow. Within weeks, 30 sperm whales had perished on cold North Sea shores.
The whales were all males, on the younger side, and likely belonged to the same pod of bachelor sperm whales, up from southern waters to feast on squid in the Norwegian Sea. Sperm whales are normally good navigators that travel from polar to equatorial seas, but somehow this group had taken a deadly detour into the shallow, relatively squid-free North Sea.
These unfortunate whales were not the first of their kind to become trapped in the North Sea, unable to find their way back to the open ocean. For centuries now, people have documented stranded whales on these coasts. Many years are free of incidents, or see only a lone example of a lost whale. But there have also been dramatic mass beachings in 1577, 1723, 1762 (when more than two dozen dead whales were found), and 1994.
For all those centuries, the cause of these mass deaths has been a mystery. Whales that die in this way tend to be in good health, with no signs of illness or malnutrition, and their deaths have come in no clear pattern that might hint at what happened. The long history of the strandings mean that it’s hard to blame humans, exclusively at least, for causing them.
In a new paper, published this August in the International Journal of Astrobiology, physicist Klaus Heinrich Vanselow and his colleagues develop a theory, first advanced more than a decade ago, that whale strandings in the North Sea are caused by solar storms. Million miles away, the Sun spits out clouds of energy and particles so large they can distort Earth’s magnetic field. When they hit the planet, these magnetic fluctuations may make whales lose their way with serious, even fatal, consequences.