Mammal Magnetism

Weddell seals spend 95 percent of their time swimming under Antarctic sea ice. They can dive to great depths and hold their breath for stretches as long as an hour at a time, even while pursuing their prey at rapid speeds. Despite this physical prowess, the seals are just as vulnerable as humans to drowning if they can’t find a breathing hole in the underwater darkness. 

How do they find their way? Lee Fuiman, a marine science professor, has hypothesized that a natural compass based on Earth’s magnetic field guides seals, helping them return to breathing holes in the ice. Terrestrial animals like homing pigeons use this trick, but no other marine mammals are known to.

A Weddell seal may swim the distance of seven football fields in minutes, following a dive path like this one in pursuit of prey. Scientists suspect the seal returns to its breathing hole with the help of a natural compass.

Fuiman struck on the idea after noticing the accuracy with which Weddell seals return to their breathing holes from a distance of a kilometer or more. Now he and a research team are using innovative sensors attached to the seals to test the hypothesis. The researchers will return to Antarctica later this year to complete a three-year project tracking seals with support from a National Science Foundation grant. The data they collect will allow the researchers to recreate the seals’ path through the water in three different locations in McMurdo Sound, each with a different magnetic field. By comparing how the seals navigate each site, the scientists hope to understand the relationship between the seals’ dive paths and their ability to sense Earth’s magnetic field.