San Francisco — Blowing and sounding, through fair weather and foul, whales and dolphins follow invisible, magnetic highways as they migrate across the trackless oceans of the world.
This is the conclusion pointed to by the research of Joe Kirschvink, an associate professor of geobiology at the California Institute of Technology. In a paper presented this week at the annual meeting of the American Geophysical Union, he offered evidence that whale strandings on the East Coast of the United States are clustered in areas where the Earth's magnetic field is weakest.
''What we think this means is that whales migrate along magnetic minima,'' explains Mr. Kirschvink. The biggest problem facing ocean-faring animal migrants - just as it was for early human sailors - is determining east-west drift. Estimating latitude is much simpler because it is straightforwardly related to the sun's height at noon.
It took the invention of a precise, portable clock before human seafarers solved the longitude problem. Now it appears that Cetacea (whales and dolphins) have achieved a similar result by the ability to sense minute differences in the strength of Earth's magnetic field. This allows them directly to sense the magnetic minima, which tend to run north and south over long distances, particularly when at sea.
Kirschvink's study does not explain whale strandings. But ''it stands to reason that whales would be most likely to run aground in unfamiliar areas when they are migrating,'' he reasons. From this, he says, it follows that concentrations of strandings in areas where magnetic minima intersect the coast strongly suggest that the whales follow these magnetic routes as they migrate.
It took four years to assemble the data to test this hypothesis. James Mead at the Smithsonian Institution provided a computer tape recording of all the known incidents of whale and dolphin beachings from Cape Cod to Florida. The US Geological Survey was the source of a detailed survey of the magnetic-field patterns along the Eastern seaboard. And the National Center for Atmospheric Research provided a digitized representation of the coastline itself. The Caltech researcher combined these three data sets and analyzed them.
This analysis demonstrated that the odds of finding beached whales along stretches of the coast where the magnetic field strength is weakest are much higher than chance, Kirschvink reports.
There is also a lower, but still significant association between beachings and magnetic maxima as well, he says.
''Magnetic maxima do not run for long distances like the minima. So, it may be that whales use them when they wish to remain in a specific area,'' the scientist speculates.
Finding evidence of the capability in whales to sense minute variations in magnetic field strength does not come as a big surprise, although it is a capability that people appear to lack. Previous research has established that honeybees and homing pigeons are sensitive to magnetic fields and use them to navigate in certain situations. In addition, Michael Fuller at the University of California, Santa Barbara, has discovered tissue with magnetically sensitive material in the heads of some cetaceans.