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European eel (Anguilla anguilla)

Also known as: eel

Illustration: Sarah Rot

Morphology & Biology

The European eel (Anguilla anguilla) is a long, thin bony fish within the order anguilliformes. Their average lifespan is 15-20 years, in which the males can grow up to 50cm and the females up to 130cm. They can endure water temperatures from 0 – 30°C and can be found in Europe, from Iceland to the North of Africa. Eels eat all kinds of marine invertebrates, such as worms and crabs.

Eels are able to swim both forwards and backwards, and can slither for short distances over land, making them one of the most able and agile fish species in European waters. 

The European eel is a highly migratory species. While there is some understanding of the eel’s continental life history, relatively little is known about their marine phase. Scientists think that eels are born in the Sargasso Sea east of Florida. The tiny larvae then float east with the current of the Gulf Stream until they reach the coasts of Europe.This will be around three years and about 6000km later. At this point, the tiny eels are only about seven centimeters in size and completely transparent. These glass eels then migrate up rivers, where they grow into adult yellow eels over the next few years. When the eels reach sexual maturity, they go through another metamorphosis in which their backs turn silvery, their eyes grow larger, and their head changes to a more pointed shape. Now – at the age of 10-30 years – the eels are ready for their long journey back to the Sargasso Sea, where they were born. Without feeding even once, they travel the entire distance back to reproduce – after which they die. Eels reproduce only once, at the very end of their long, incredible lives.

Lifecycle of the European eel (Source: Henkel et. al 2012, PLOS ONE)

Threats

Eels have existed for about 100 million years. They have survived the ice ages and adapted to tremendous climatic changes and shifting of continents. The eel was once one of the most abundant fish in the European freshwaters and their range extended from northern Africa to the Arctic Circle. But now the survival of the eel is in serious danger because of us humans. Since 2008, the European eel has officially been an endangered species. Only 1.5% of the original population size from 1979 is left.

Many dangers await the eels on their long journey: river dams block their way and intensive river straightening has destroyed their natural habitats where they find shelter and food. Polluted water, disease, and parasites plague them, and  everywhere nets and fishing rods are waiting to pull them out of the water.

In recent years eels have become scarce in the wild – but demand for them remains high. Over time, a growing black market has developed. Today, the illegal trade of glass eels is considered one of the biggest wildlife crimes in the world, ranking with the illegal trade in ivory, rhino horn and pangolins.

The export of European eels from the EU has been banned since 2010. Nevertheless, about 350 million glass eels are illegally exported from Europe’s coasts to Asia every year – equivalent to a quarter of all European glass eels. On the black market, a kilogram of live European glass eels can fetch up to €6,000. Glass eels are in high demand, especially in China, where they are caged and fattened in aquacultures until they are the right size for slaughter.

A tiny glass eel (Photo: Biopix, N Sloth)

Fisheries & Aquaculture

Although the European eel is threatened with extinction, they are fished legally and commercially in Germany and Europe. Every year since 2008, scientists of the International Council for the Exploration of the Sea (ICES) recommend a fishing ban  for the European eel, yet every year the EU ministers allow fishing to occur anyway. This weak decision was recently disguised by an annual closed season of three months. However, this is by no means sufficient to ensure the survival of this impressive fish species.

Since 2007, the EU’s “Eel Regulation” has regulated the management of the European eel, while also aiming to allow the endangered species to recover. However, despite all efforts, meetings and subsidies, there has been no recovery of the eel population in the last 13 years. Many of the agreed upon conservation measures have not been implemented to date and set goals have not been met. The Eel Regulation is a complicated and opaque instrument that is much more dedicated to ensuring commercial eel fisheries rather than saving the European eel.

Since the demand for European eel is so high, the amount that are caught in the wild are not sufficient to keep up with demands. As a result, European eels are being bred in aquacultures all over the world. But what hardly anyone knows is that eels do not reproduce in captivity. Every single eel that is raised in aquaculture was taken from the wild as a juvenile. Therefore, aquaculture is not a solution for the endangered eels, but an additional threat.

Fishing for glass eels, along with environmental pollution and other human impacts, have contributed to a significant decline in eel numbers over the last 25-30 years. The total volume of glass eels collected every year is around 150 tonnes, of which 100 tonnes are used as “seeds” in aquaculture and 50 tonnes going to Spain for human consumption.

Fun fact

Even Aristotle was fascinated by eels. He noticed that ponds were filled with eels after the rain and believed that European eels grew or were ‘born’  in the mud and may have possibly developed from earthworms. He didn’t know that eels can slither over land for short distances and therefore end up in ponds.

Sigmund Freud studied eels at the Adriatic coast and wanted to discover how the species reproduced. After investigating hundreds of eels, he found that none had reproductive organs. This was because the eels were not mature yet, only when they return to the Sargasso sea are the reproductive organs developed.

Two eels sharing a hole in the sea bed (Photo: Biopix, N Sloth)

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