09 June 2017 – The odyssey of the European eel begins when they hatch in the Sargasso Sea. As little leptocephalus larvae, they travel thousands of kilometers across the Atlantic Ocean, hopefully making it to the European continental shelf. When eel leptocephali arrive at the continental shelf, they metamorphose into transparent glass eels, changing shape, physiology and behavior. At some point during this journey – anywhere from the Canary Islands to northern Norway – they “hop off” the Gulf Stream and actively migrate towards the coast, heading for estuaries. Some eels remain in the coastal area, while others move inland into lakes, remaining there, slowly growing, for up to 30 years. How glass eels “hop off” the Gulf Stream towards the coast and find estuaries is a long-standing mystery.
To understand how these small fish manage to find the coast, a research team at the Norwegian Institute of Marine Research‘s Austevoll Research Station, in collaboration with the Physical-Biological Interactions Laboratory at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, assessed whether glass eels use the Earth’s magnetic field to guide them towards the coast. The study, “Glass eel (Anguilla anguilla) have a magnetic compass linked to the tidal cycle”, published today in the AAAS journal Science Advances, reports that glass eels use a magnetic compass, modulated by an internal tidal clock, to orient towards the coast. In other words, young eels can sense the Earth’s magnetic field, use it as a frame of reference for orientation, and change direction according to the tidal cycle.
University of Miami Doctoral student Alessandro Cresci has been investigating the orientation behavior of glass eels using a unique combination of experiments conducted in a magnetoreception test facility (the “MagLab“), and in a Norwegian fjord, the natural environment of the glass eel just before it arrives at the coast. In the study, glass eels were observed in a neutrally buoyant aquarium (Drifting in situ Chamber, DISC) designed so that they could orient while drifting with the current under the environmental conditions that they would encounter during their migration towards the coast. The same eels were also tested in the MagLab, where the magnetic field to which they were exposed was artificially manipulated such that the N-S and E-W axes were shifted by 90 degrees. Although deprived of all other environmental cues, glass eels in the laboratory oriented to the South, the same direction that they swam in situ during the ebb tide.
“It is incredible that these small transparent glass eels can detect the Earth’s magnetic field. The use of a magnetic compass could be a key component underlying the amazing migration of these animals,” says Cresci.
This study is an important addition to our understanding of the mechanisms of eel migration and also to that of other species if it turns out that their magnetic orientation is similarly modulated by a biological clock.
Read the article: A. Cresci, C. B. Paris, C. M. F. Durif, S. Shema, R. M. Bjelland, A. B. Skiftesvik, H.I. Browman, Glass eels (Anguilla anguilla) have a magnetic compass linked to the tidal cycle. Science Advances 09 Jun 2017: Vol. 3, no. 6, e1602007, DOI: 10.1126/sciadv.1602007