How do cetaceans find their way over long distances?

A humpback whale that leaves the Antarctic in April arrives in July in the same Polynesian bay it left the previous year, to within a few kilometres. A resident killer whale of the North-East Pacific knows, across an area of several tens of thousands of square kilometres, the precise places where chinook salmon pass on one date or another. A male sperm whale, after a decade feeding at high latitudes, finds its way back to the tropical waters where its maternal units travel. None of these animals has a GPS, a chart or a compass. How do they do it?

The question is open and fascinating. Several senses appear to contribute, in varying proportions depending on the species and the circumstances. No simple, unified answer exists. Research over the past thirty years has identified at least five plausible mechanisms, which probably act as complements to one another.

The Earth’s magnetic field, an indirect cue

The idea that cetaceans perceive the Earth’s magnetic field rests on several converging lines of evidence, but on no direct physiological demonstration. The oldest is statistical: the biologist Margaret Klinowska showed in 1985 that mass stranding sites in Great Britain are concentrated where the magnetic field lines show particular anomalies, either because they converge at a point or because they run perpendicular to the coast. The hypothesis: cetaceans would follow these lines to orient themselves, and when the lines lead them into shallow coastal areas, they strand.

Similar studies have since been carried out in other parts of the world, with broadly converging results. More recently, Vanselow and colleagues (2018) showed that solar storms, which briefly disturb the Earth’s magnetic field, are correlated with peaks of sperm whale strandings in the North Sea. Granger et al. (2020, Current Biology) found the same kind of correlation in Pacific grey whales: their strandings are statistically more numerous on days with high atmospheric radio-frequency noise.

On the physiological side, several studies (Bauer et al., 1985; Walker et al., 1992) have found magnetite crystals in the brain and meningeal tissue of common bottlenose dolphins and sperm whales. Magnetite is a magnetic mineral also present in bees, migratory birds and certain bacteria, where it plays a proven role in magnetic perception. In cetaceans, however, its functional role has not been demonstrated beyond doubt: the parts are there, the complete mechanism is not.

Topographic memory

The seabed is not a uniform plain: it is structured by canyons, seamounts, ridges, trenches and continental slopes. These structures remain stable over millions of years. For an animal able to memorise them and to recognise them by echolocation or by passive acoustic sounding, they make a reliable chart.

The sperm whale closely follows the continental slopes and the submarine canyons, where cephalopods concentrate. Humpback whales return year after year along strikingly precise routes. Resident killer whales know their area in a degree of detail that recalls a hunter on ancestral ground. This knowledge is passed on by accompanying the young: the matriarch of a pod shows, through practice, the routes and the productive areas.

Ocean soundscapes

The ocean has a coherent acoustics on very large scales. The sound of waves on coastlines, the rumble of submarine earthquakes, the hiss of rain at the surface, the songs of other whales: all of this makes up a stable soundscape that cetaceans can use as a landmark.

Stafford and colleagues showed as early as 1998 that blue whale songs are detectable at more than two thousand kilometres under certain conditions, thanks to the SOFAR channel (see our page on long-distance communication). If a whale can hear the songs of its own kind hundreds or thousands of kilometres away, it has a powerful directional reference. It is a sense whose usefulness we, vision-dominated humans, struggle to imagine.

Currents and temperatures

The great ocean currents, the Gulf Stream, the Kuroshio, the Agulhas Current, the Antarctic Circumpolar Current, are persistent structures. Their boundaries are marked by thermal fronts, where the water temperature changes abruptly, and by salinity gradients. For an animal sensitive to these variations, they are so many beacons.

Humpback whales, for example, follow the front of the Agulhas Current along the African coast, and fin whales exploit the seasonal thermal fronts of the North Atlantic. This navigation by gradients is probably reinforced by other sensory cues: smells, suspended particles, phosphorescent plankton visible at night.

When orientation is disturbed

The very existence of these orientation systems is confirmed by their vulnerability. When mid-frequency military sonars acoustically disturb beaked whales, the animals flee to the surface and strand (see our page on military sonars). When solar storms upset the magnetic field, strandings increase. When shipping traffic noise saturates the low-frequency band, blue whales lose their long-distance acoustic reference. Each time, this is indirect evidence that a sense existed, and that it was essential.

Which of these senses is dominant, magnetoreception, acoustics or topography, remains largely an open question. A hypothesis increasingly shared among researchers is that cetaceans combine this information redundantly, as human pilots combine GPS, magnetic instruments, visual landmarks and speed calculations. No system works alone; all of them work together.

Sources

• Klinowska, M. (1985). “Cetacean live stranding sites relate to geomagnetic topography”. Aquatic Mammals, 11.
• Vanselow, K.H. et al. (2018). “Solar storms may trigger sperm whale strandings”. International Journal of Astrobiology.
• Granger, J. et al. (2020). “Gray whales strand more often on days with increased levels of atmospheric radio-frequency noise”. Current Biology, 30.
• Stafford, K.M., Fox, C.G. & Clark, D.S. (1998). “Long-range acoustic detection and localization of blue whale calls in the Northeast Pacific Ocean”. JASA, 104.
• Walker, M.M. et al. (1992). “Detection of magnetic field by cetaceans”. Animal Behavior.

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Further reading