New research from the University of Miami and Norway's Institute of Marine Research has found that the European eel at a certain stage of development use an internal magnetic compass to remember the magnetic direction of tidal waves as they navigate the waters.European eels are a migratory species that hatch in the Sargasso Sea and then as laevae 5,000 kilometers to Europe's continental slope. There they turn metamorphosize into a transparent larval stage called 'glass eel' and continue to Europe's coast and enter estuaries.Some of the eels continue to swim upstream to freshwater. Eels that get there then grow into the adult eel stage, which is yellow in color. These eventually become sexually mature, silver eels.Scientists gathered 222 glass eels flowing in four different directions north, southeast, south and northwest from separate estuaries in Austevoll, Norway and put them in a magnetic laboratory facility, according to a study published in the journal Communications Biology. When the lab's magnetic north was rotated, they observed that the eels turned towards the magnetic direction of the tidal current at their estuary.The researchers mentioned in the study that this mechanism could be helpful to eels if they lose visual reference points as they move upstream during migration. The eels' magnetic compass could also be used years later when they are silver eels as they return to the Sargasso Sea to spawn and pass away.