The common or European eels, Anguilla anguilla , carry out a spectacular migration in which they travel about 8,000 kilometers, from Europe to the Sargasso Sea, near the Bermuda Islands, where these fish lay their eggs. The larvae that hatch from them, called leptocephalos, are practically transparent and have a markedly different appearance from adults. These return to the Old Continent and penetrate the rivers. Then, they undergo remarkable physical changes and, over time, they acquire the size and appearance of their elders. However, there are many details that are still unknown about the journey that these animals follow .
Now, a team of researchers from different European institutions has presented the results of a meticulous study on this species, in which they have worked for more than ten years. Thus, as these experts explain in an article published in the journal Science Advances , when they are barely two centimeters tall, the baby eels, that is, elvers, travel from the Sargasso Sea to the European rivers, where they live between five and twenty years. At that time they become adults, but before they undergo two metamorphoses. When they reach maturity, they return to the aforementioned Atlantic region to spawn.
To determine this, the scientists, including Francisco Javier Lobón-Cerviá, from the Evolutionary Ecology Department of the National Museum of Natural Sciences (MNCN-CSIC), in Madrid, placed transmitters on 707 grown specimens. These were released in different areas of Europe – eels can be found from the Kola Peninsula, northern Russia, to the Mediterranean and even in the Canary Islands. Later, they received data from 206 of them and followed 80’s journey in detail.
“We have discovered that they follow a routine when it comes to moving. During the day they move in the depths and, when night falls, they continue their journey in shallower waters,” says Lobón-Cerviá. The test shows that not all eels make this journey in four months to spawn simultaneously –this lasts from December to February–, as was believed, but that many take up to a year to arrive. Specifically, the average duration of the trip of those that were marked, which traveled between 3 and 47 kilometers per day, was eleven months.
“The data has helped us to clarify many details of this complex migration and we have significantly improved our knowledge about the dynamics of its population. Thus, we can improve the conservation and management strategies of the species to protect it,” says Javier Lobón-Cerviá.
Imagen: LFL / Institute for Fisheries
