It's been over a year since 29 sperm whales washed up on the shores of Germany, the Netherlands, the United Kingdom and France in a mass stranding event that grabbed headlines across the globe. And now, scientists have proposed an interesting explanation for the mysterious deaths.

Despite what the vandals who spray-painted the whale carcasses would have you believe, the culprit behind the strandings was not radiation from the Fukushima nuclear disaster, but the most recent hunch does point to a radioactive source: the one that sustains life on our planet. 

The strandings began in January of 2016, and in the months since, necropsies have revealed that most of the washed-up sperm whales showed no sign of disease or injury. With environmental contamination and illness ruled out, a team led by Kiel University researcher Dr Klaus Heinrich Vanselow turned their attention to the sky for answers. 

An artist's illustration shows how events on the sun change the conditions in near-Earth space. Image: NASA

A month prior to the first whale death, a pair of major solar storms painted the skies of the Northern Hemisphere in shades of green and pink. These spectacular displays arise after the Sun catapults particles of plasma (solar wind) into space. It takes nearly two days for that wind to hit Earth, but when it does, the particles within interact with our atmosphere and cause the bursts of light we know as auroras.

This particular storm duo resulted in an aurora borealis so vivid it could be seen as far south as Scotland. And the Kiel University team suspects the storms may have also caused migrating whales to stray off course. 

To be clear, Vanselow and his colleagues do not believe the lights themselves caused the animals to strand (headlines that suggest this are a bit misleading). In fact, we've seen whales behaving normally under glowing night skies, as seen in this clip filmed off the coast of Norway:

Instead, the researchers postulate that changes in Earth's magnetic field may have steered the whales into a relatively shallow swathe of the North Sea.

The hypothesis is certainly intriguing, but confirming it will be challenging. Some evidence has emerged that other animals, like birds and flying insects, are indeed affected by solar storms – but it's unclear whether this is the case with whales, too. For starters, we still don't know if these marine mammals actually navigate using Earth's magnetic clues. What's more, how sperm whales make group movement decisions (if they do at all) is still being studied.  

"No one has proven [that whales] have any ferrous substances in their brains," explains comparative anatomist Dr Joy Reidenberg, who has done extensive work on sperm whales. "Finding this is harder than you might think."

To test for ferrous fluid, which contains magnet-sensitive iron, scientists would need to search for trace levels in the brain. Any metal in their instruments, however, could easily contaminate the samples taken: it would be difficult to discern whether detected iron deposits came from the animal or the scientists' tools. "You can't use a metal knife made with any iron or metal composites with iron in it," explains Reidenberg.  

And because sperm-whale skulls are extremely thick – around a foot (30cm)! – breaking into one without the help of metal instruments is almost impossible. "It's really hard to cut open a sperm whale's skull (or any other whale for that matter) and get to the brain using only glass knives!"

Going in through the much squishier eye wouldn't work either because the opening between the eye socket and brain cavity is only big enough for the optical nerves to pass through. What's more, we don't know where in the brain any potential iron deposits might be lurking, so taking a small tissue biopsy could easily miss them.

"Even if we could go in through the eye socket, what tools would we use to cut out the brain tissue?" asks Reidenberg. "They can't be metal or have metal handles, or that would contaminate the sample! The whole brain is probably necessary. It would need to be examined, perhaps imaged – but not on an MRI, as the iron would move in the magnetic field." 

But for the Kiel University team, certain clues about this particular case do point to some level of magnetic awareness in the affected sperm-whale population. 

As we've discussed before, the topography of the North Sea floor can act like a whale trap under certain conditions, and once lost leviathans swim into such areas, they can struggle to navigate their way back out. Local sperm whales appear to stay on the outside of an underwater mountain chain that acts as a barrier between the open ocean and the North Sea's topographical trap. That chain emits a unique magnetic signature, so it's possible that the whales actively use it as a guide rail. If this is the case, magnetic fields warped by the solar storms may indeed have confused the animals' internal compasses and concealed their mountainous guide. 

"Failure of whales to account for disruptions in the magnetic field, such as those triggered by random and abrupt solar storms, may thus lead to temporary navigational errors and disorientation," the team writes in the International Journal of Astrobiology 

And even if sperm whales are not using the mountain chain as their path-finding guide, an increase in magnetic intensity could still have triggered a false impression of a more northerly position, prompting any whales to correct their path by heading south. As those fields returned to normal, the decrease in intensity would've had the opposite effect. 

Interestingly, many of the whales that washed up last year were juveniles, which seems to bolster this theory. Vanselow and the team note that youngsters may be more prone to geomagnetic stranding because of their inexperience with solar anomalies.

Many sperm-whale nursing grounds are situated in temperate waters, close to the equator – and that means juveniles would encounter serious magnetic shifts only as they moved towards the poles on their first migrations. Polar regions experience the most significant change after solar storms (that's why we see auroras in these areas).

The solar events in question may have shifted magnetic fields around the North Sea up to 280 miles. In theory, that's certainly enough to prompt a dangerous change of course for passing whales – especially inexperienced youngsters. And once the animals steered in the whale trap, they would have become fatally stuck. The explanation is a plausible one, but the enigma is far from solved. 

The idea that whales and their cetacean kin are affected by solar storms has been floating around for some time, but scientists are only just beginning to investigate how valid it might be. In fact, even NASA is studying the potential effects of such events. 

"It's a long-standing mystery and it's important that we figure out what's going on," says NASA heliophysicist Antti Pulkkinen, an expert in space weather and its effect on the Earth. "Magnetic anomalies could be at least partially responsible."

Pulkkinen and the NASA team believe the recent study is well founded, and plan to publish their own research on the topic in the coming year. The hope is that by comparing global stranding-network and space-weather databases, we may begin to clarify the possible link between them with greater confidence.  

Other experts, like Dominica Sperm Whale Project founder Shane Gero, note that strandings of this nature probably arise from a complex mix of factors – one that may never be explained by a single, simple explanation.

"For me the bigger picture question this brings up is, can whales adapt quickly to changes in their environment,” he says. "Whether it's short-term, abnormal changes in magnetism from solar storms, progressively louder ocean noise from increased shipping, or climate change driven ecosystem-wide disruptions; can whales be expected to respond quickly enough and change their behaviour to survive? I am happy and excited that researchers in a diversity of fields are working to better understand sperm whale behaviour, and particularly how we might mitigate potential causes of their deaths."



Top header image: marie-ll/Flickr