Analysis of grey whale stranding incidents has supported speculations that the migratory mammals rely on a magnetic sense, rather than the Earth’s geomagnetic field, to navigate their way around the ocean.
Whales tend to get stranded on beaches when there are more sunspots, which are strongly related to solar storms – sudden blasts of radiation from the sun that can disrupt the Earth’s outer magnetosphere.
Jesse Granger, from Duke University in the US, and colleagues used this observation to explore what cues whales use to achieve their “impressive feats of navigation”, publishing their findings in the journal Current Biology.
The solar storms “could alter the geomagnetic field, leading to false information, or disrupt the animal’s receptor itself, leading to an inability to orient,” they write.
“Is it that the solar storms are pushing the magnetic field around and giving the whales incorrect information – for example the whale thinks it is on 4th Street, but it is actually on 8th?” says Granger.
“Or is it that the solar storms are messing up the receptor itself – the whale thinks it is on 4th Street, but has just gone blind?”
Grey whales (Eschrichtius robustus) presented an ideal target for the investigation.
They are one of the Earth’s most prolific migrators, sometimes travelling more than 19,000 kilometres in their seasonal roundtrip between Alaskan and Mexican waters while staying close to shore, rendering them vulnerable to small navigational glitches.
The scientists used three decades of data on 186 grey whales that had been found stranded alive with no signs of illness, injury or human interactions that could account for their predicament.
Their initial analysis showed that these accidental forays more than doubled on days with high sunspot counts, indicating magnetic influence.
They then teased out this relationship with two aspects of Earth’s magnetosphere impacted by solar storms: radio frequency noise, found to disrupt magnetic orientation in migrating birds, and interruptions to the planet’s magnetic field.
To their surprise, the likelihood of stranding was more than four times greater during high radio-frequency noise, while there was no association with large deviations in the magnetic field.
The authors conclude, therefore, that “the increased strandings under the high solar activity are best explained by an effect on the sensor, not on the magnetic field itself”.
Granger emphasises this isn’t the only cause of strandings – others include naval mid-frequency sonar, disease and human activity – and plans to investigate other species around the globe to shed more light on whales’ magnetic sense.