Every autumn, eels from across the world migrate to the breeding grounds in the Sargasso Sea in the mid-Atlantic. Once they have spawned their eggs, the next generation will be carried by the Gulf Stream to the North Sea and into the Baltic.

A tenacious 50-year-old
“The eel undergoes a number of transformations during its lifetime from when, as an egg, it flows out from the Atlantic spawning area. When it reaches the waters around the Fehmarnbelt, it is limpid. Later, it becomes yellow and more stationary. When, at the next stage of its life, it is ready, it will head towards its original home once again,” explains marine biologist Maks Klaustrup, Orbicon│Leif Hansen A/S.

“The eel is a tenacious fish which can reach the age of fifty or more, and can live in salt water, brackish water and in fresh water,” says Maks Klaustrup. “We don’t know why they choose one moment instead of another to return to their original home. Some do it when they are six while others wait until they are fifty. We also don’t know with any degree of certainty how the eel finds its way back to the Sargasso Sea. But we do know that when leaving the Baltic it passes either through Guldborgsund, Øresund or the Fehmarnbelt.

Eel logbook
Maks Klaustrup is researching into eel migration and the possible consequences of a fixed Fehmarnbelt link on the eel population.

“We are currently mapping eel migration and the routes they take so we can see the impact of a fixed link on eel migration,” he says. “If, for instance, it becomes clear that the majority of eel migrate through Øresund, the fixed Fehmarnbelt link would probably have a limited impact.”

Local networks play a part
The eels are tagged and subsequently caught by Danish and German fishermen. As the tag is important to the project, a competition has been organised to encourage the fishermen to return as many tags as possible to Maks Klaustrup and the rest of the investigation team.

The initiative has been publicised in advertisements in the specialist publication, Fiskeritidende, through local networks and by word of mouth. “So far, it has all been highly successful,” Maks Klaustrup says. “During 2008, we tagged around 2,000 eels and got 270 tags back from fishermen. We’re delighted with that.”