Critically endangered eels arriving in our Flemish rivers after a 6000 kilometer journey | Flanders Marine Institute

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Critically endangered eels arriving in our Flemish rivers after a 6000 kilometer journey

Ostend (2017.03.20) – With spring hanging in the air, glass eels are arriving at the Flemish coast. Coming from the Sargasso Sea they currently are swimming up rivers and channels, a journey full of obstacles. Here and elsewhere in Europe, the numbers of arriving glass eel dropped drastically to a fraction (2%) of the numbers arriving 50 years ago. One of the main reasons for this sharp decline and their status as 'Critically Endangered' species are the many barriers that adult eel experience in their migration route towards the sea to spawn. Within the LifeWatch project, the Flanders Marine Institute (VLIZ), Ghent University, the Research Institute for Nature and Forest (INBO) and VLAIO investigate this migration with tags and receivers. An animation (see below) illustrates these findings.

Press release by: Flanders Marine Institute (VLIZ) and LifeWatch Belgium, in cooperation with UGent and INBO

The European eel (Anguilla anguilla) is one of our most famous fish species. Despite years of research, it is not possible yet to culture eels. Eel farms do exist, however they need to buy young wild eel to fatten. Due to human consumption and overfishing the eel population dramatically declined since the 70s by 98%. Other factors such as migration barriers (dams, locks ...), water pollution, diseases and parasites, as well as climate change play a role in their declining abundances.

This same decline is also evident in the glass eel arrival at our coast. Each spring (between February and May) young, 5 to 10 cm long transparent eels (‘glass eels’) migrate from marine to fresh waters. Surveys in recent decades show that the numbers of glass eel arriving are only a small percentage of the numbers swimming up our rivers 50 years ago. To enable glass eels to colonize fresh water, Belgium adapted its drainage management for some years now - based on research of INBO. In the eels' migration period the Flemish water manager (Waterways and Sea Channel NV) leaves the sluices ajar during high tide.

A few years later, when the eels are mature, they develop into the so-called ‘silver eel’ stage. Having bigger fins and a change in color they start to migrate for 6000 km towards the Sargasso Sea. With a dark gray back and a silvery white belly they are better camouflaged against predators. During the full period of migration to the Sargasso Sea they do no longer eat and their digestive system languishes. Just like the young glass eel, but in the opposite direction, adult silver eel encounter a lot of obstacles in their way (hydroelectric power plants, pumping stations, dams and locks). In order to gain insight into eels passing these sometimes dangerous migration bottlenecks in their journey to the sea, the European project LifeWatch started tagging and tracking of silver eels. VLIZ, INBO, Ghent University and VLAIO have built a network of receivers in rivers and the coastal area to register tagged individuals. The information obtained in this way helps water managers to pave the way for migratory eels as much as possible.

Meanwhile, the LifeWatch study suggested a new migration route for the European eel. Contrary to the general perception that emigrating silver eel is leaving the North Sea through the northern exit, the LifeWatch monitoring shows that the southwestern route – through the English Channel –  may play a significant role as indicated by the passage of Belgian, Dutch and German eels off the Belgian coast. Taking this shortcut saves the eels a lot of energy, being favorable for a better reproduction. Another possible consequence is that control measures are preferably taken in those countries where eels are taking the short route (like in Belgium and The Netherlands).

To informing a broader public about the problems of the European eel and the findings of the tagging research programme, VLIZ made a short animated video (3 minutes) for LifeWatch Belgium.

Press contact

Pieterjan Verhelst
UGent - Marine Biology Research Group
T: +32 (0)9 264 85 17
GSM: +32 (0)499 38 72 87