Quirks & Quarks

Infant eels use the moon and an internal compass to finish their transocean migration

European eels cross the Atlantic Ocean twice in their lifetime, once after birth, and once to breed

European eels cross the Atlantic Ocean twice in their lifetime, once after birth, and once to breed

The European eels' migration depends on them navigating by moon and internal compass (Alessandro Cresci)

The European eel has a complicated and fascinating life — full of travel and personal transformation. But how it navigates an incredible journey in the first part of its life, when it crosses the Atlantic Ocean to get to European waters, and then back down again has largely been a mystery until now. 

According to the lead researcher of two recently published studies, marine biologist Alessandro Cresci at the University of Miami, the European eels owe their navigational abilities to the moon and an internal compass.

Transformation along their migratory route 

Baby eels hatch in the Sargasso Sea, east of Florida and the Bahamas, and travel more than five-thousand kilometres as a larvae to Europe. 

Once the larvae hit the continental shelf, they metamorphose into transparent "glass eels" — a delicacy in many European countries, which has sadly made them a critically endangered species. 

Mickael Vallee, a professional fishermans, holds glass eels he fished on the Loire river in western France. European eels are currently listed as critically endangered. (Jean-Sebastien Evrard / AFP via Getty Images)

The eels head into estuaries on their way to freshwater rivers and streams where they mature and live for years before another great migration back to the Sargasso Sea to spawn and die.

Travel by lunar cycle

To study the glass eels in their natural habitat, Cresci put single glass eels into a transparent chamber equipped with cameras and a compass to see where the eels wanted to go.

Cresci had a strong suspicion lunar cycles were involved as the European eels most often arrive in Europe during the new moons. 

Alessandro Cresci deploys a Drifting In Situ Chamber (DISC) with an eel inside of it to monitor the direction the eels would point in during various lunar phases. (Alessandro Cresci)

He discovered that during the new moon cycle, the glass eels would turn toward the moon, which — as they're drifting up the Gulf Stream — would lead the eels to turn right and fan out to the European coast.

Travel by internal compass

The glass eels that reach the estuaries use another mode of navigation for when they arrive in Europe and travel up freshwater rivers and streams: their internal magnetic compass.

Cresci collected glass eels from various estuaries in Norway. As the tides ebb and flow, the direction of the currents change every six hours. In order for the eels to migrate upstream and not get swept out to sea again, he discovered the eels use their magnetic compass to imprint the magnetic direction of the tidal flows. 



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