A recent article in The Atlantic discusses the fascinating possibility that whales make use of the Earth’s magnetic field to help them navigate the oceans.
As I explain in Incredible Journeys, many great whales (including notably the humpbacks that migrate annually between the Antarctic and equatorial waters) regularly travel for thousands of miles across the apparently featureless open ocean following remarkably straight courses. Since they seem to be able to do this even when the sky is obscured, it seems unlikely that they rely on celestial cues (like the sun or stars) to perform these feats - though it’s conceivable that they can do that too in fine weather. The omnipresent geomagnetic field (see my earlier post ‘The great magnetic mystery’) would however be available to them at all times and places - and all depths.
The theory that whales may be magnetic navigators (like many other animals including some birds and insects) has been around for a long time. But Jesse Granger and her colleagues at Duke University have recently published some interesting work based on a review of data gathered over a 31-year period. They wanted to find out whether solar storms that disrupt the Earth’s magnetic field are correlated in any way with strandings of gray whales.
They looked at 186 strandings involving apparently healthy whales (injured or sick animals might get stranded for other reasons) and parallel data relating to levels of solar activity. They found that the two were indeed closely correlated.
So what’s going on?
As Granger et al. explain, ‘Solar storms could have two impacts on magnetic orientation. They could alter the geomagnetic field, leading to false information, or disrupt the animal’s receptor itself, leading to an inability to orient.’ But the key factor influencing the strandings appeared to be the increase in radio frequency ‘noise’ associated with the solar storms rather than any displacement of the Earth’s magnetic field.
Granger et al. conclude: ‘These results are consistent with the hypothesis of magnetoreception in this species, and tentatively suggest that the mechanism for the relationship between solar activity and live strandings is a disruption of the magnetoreception sense, rather than distortion of the geomagnetic field itself.‘
There is evidence from studies of migratory robins that RF noise (from AM radio transmitters) can disrupt the magnetic compass sense of these birds. It’s possible that the hypothetical cryptochrome magnetoreception mechanism may be disrupted by such transmissions. So, as Granger et al. acknowledge, it’s conceivable that whales may also rely on a cryptochrome-based magnetoreceptor. But it’s far too soon to start laying bets!
One thing that puzzles me is that gray whales - which tend to follow the coast on their migratory journeys rather than crossing the open ocean - should be so heavily reliant on magnetic information that they would get stranded if it was disrupted. Could they not simply use landmarks or the contours of the sea floor to help them find their way? And even if they did rely on their magnetic sense of direction, you’d think that they would notice when the water began to shoal and turn back before they went aground. It’s odd.
The humpbacks by contrast are prodigious oceanic navigators and it makes sense that they would rely on geomagnetic cues when out of sight of land. Interestingly their migratory journeys often seem to feature visits to underwater features called seamounts. Could it be that these act as waymarks? Maybe they even have unusual magnetic properties that the whales can detect?
Apparently Granger is now looking at 12 years-worth of data relating to humpback whale voyages. She wants to see whether they have more difficulty maintaining straight courses when solar storms hit the Earth.
That should be interesting!
