How the Eel Crossed the Atlantic

Anyone who has let their cat roam free over the neighborhood knows how keen a cat’s sense of direction can be. After all, they always find their way home–or so they saying goes. The European eel can do something quite similar, but its neighborhood stretches across the entire North Atlantic Ocean. Scientists are finally beginning to understand how these eels coordinate such a fantastic feat of navigation.

Scientists have long marveled over the young eels’ ability to find their way from their birthplace in the Sargasso Sea–off the coast of the southern United States–to the regions on the other side of the Atlantic where they spend most of their adult lives. They began to suspect that the eels, like plenty of other animals, use the earth’s magnetic field to navigate.

The earth’s churning hot metal core creates a magnetic field that surrounds our planet, providing practical benefits like protecting us from solar wind and allowing us to use a compass to figure out which direction is north. Some animals can even tap into this magnetic field to navigate, since each spot on earth’s surface is exposed to a different magnetic field due to its unique location between the earth’s poles.

Which leads us back to the eels. According to results published in the journal Current Biology, a group of researchers wanted to know how the eels would swim when exposed to different magnetic fields. To test this, they grew the eels in large tanks and exposed them to magnetic fields that would be characteristic of different geographic locations that the eels could occupy during their life cycle. Based on the results that they recorded in the tank, scientists could figure out how the eels would swim in the open ocean with a corresponding natural magnetic field.

Interestingly, this experiment showed that the magnetic fields would sweep the eels right into the Gulf Stream. We have all heard about the Gulf Stream, especially on the Weather Channel. In this context, though, the Gulf Stream is an ocean current that circulates around the North Atlantic in a clockwise direction.

The researchers concluded that the magnetic field would lead the young eels to the Gulf Stream, then the clockwise gyre of the Gulf Stream would lead them from the Sargasso Sea to Europe to spend their adult lives. Later in their lives, when it is time to return to the Sargasso to spawn, the eels would use the magnetic map to find the Gulf Stream again to return to where they started.

The researchers noted that this is the first evidence that eels use a magnetic map to coordinate their massive migrations, adding another species to the list of animals finding their way around earth with their very own internal compass.