Why Are European Eels Critically Endangered? Causes of Decline

How steep is the decline?

The best measure of the European eel population is the number of glass eels, the tiny transparent young that arrive from the ocean each winter and spring. Scientists have counted them at river mouths across Europe for decades, and the trend is stark.

After high numbers in the late 1970s, arrivals crashed in the 1980s and have stayed low ever since. According to the joint working group on eels of ICES, the international marine science council, glass eel recruitment in 2024 was about 1 percent of the 1960–1979 average in the North Sea region and about 7 percent in the rest of Europe. In other words, the decline has been around 90–99 percent depending on the region.

The IUCN Red List first classified the European eel as Critically Endangered in 2008, its highest category for species still living in the wild, and reassessments in 2014 and 2020 confirmed that status.

Dams, weirs and hydropower turbines

Eels need open rivers twice in their lives: once as young eels swimming upstream, and again as adult silver eels swimming down to the sea. A 2020 study counted more than 1.2 million dams, weirs, culverts and other barriers in Europe’s rivers, many of them small and unmapped.

Every barrier can stop or delay young eels and shrink the area of river they can live in. On the way down, silver eels passing through hydropower turbines and pumping stations can be injured or killed, and losses add up on rivers with several plants. Studies have found that eel numbers dropped more steeply in rivers with large dams than in rivers without them.

Overfishing at every life stage

Eels have been fished in Europe for thousands of years, and they are caught at almost every stage of their lives: glass eels in estuaries, growing yellow eels in rivers and lakes, and silver eels on their way to the sea. Because each eel breeds only once, at the end of its life, every eel caught before it reaches the Sargasso Sea is one less spawner.

As stocks fell, glass eels became extremely valuable. Prices rose sharply in the late 1990s when demand from eel farms in East Asia increased, encouraging even more fishing of the youngest eels.

Illegal trafficking of glass eels to Asia

Since 2010, the European Union has banned all exports of European eels outside its borders. Demand remained, however, because eel farms in China and elsewhere in East Asia rely on wild-caught young eels to supply a large market for grilled eel dishes. Criminal networks began smuggling live glass eels out of Europe, often packed in suitcases or hidden among other cargo.

Europol, the European Union’s police agency, has estimated that in some years up to around 100 tonnes of glass eels, hundreds of millions of fish, were smuggled out of Europe, making it one of the continent’s most serious wildlife crimes. Coordinated police operations since 2016 have led to hundreds of arrests and the seizure of many tonnes of live eels.

The swim bladder parasite from Asia

In the early 1980s, a parasitic roundworm called Anguillicola crassus reached Europe, most likely with imported live Japanese eels. In its native host, the Japanese eel, it causes little harm. In European eels it lives in the swim bladder, the gas-filled organ that controls buoyancy, and it can thicken and damage the bladder wall.

The parasite spread across much of Europe within about a decade, and in many waters a large share of eels are now infected. Scientists suspect that eels with damaged swim bladders may struggle to complete the deep, months-long ocean migration to the Sargasso Sea.

Pollution, habitat loss and a changing ocean

Eels are long-lived, fatty fish, so they build up pollutants such as PCBs, dioxins and pesticides in their tissues over many years. These chemicals are released into the blood as the eel burns its fat during migration, and studies suggest they may harm the development of eggs and larvae.

Large areas of wetland, marsh and floodplain where young eels once grew have been drained for farming and building. At the same time, changes in the North Atlantic, including shifts in ocean temperature and currents, may affect how many larvae survive the long drift to Europe. Scientists still debate how much each of these factors matters, but together they make recovery harder.

What is being done to save the eel?

Several measures are in place:

• EU Eel Regulation (2007): every member country must run eel management plans with the long-term goal of letting at least 40 percent of the silver eels that would have existed without human impact escape to the sea. A share of the glass eels caught must also be used to restock European waters.
• Trade controls: the European eel has been listed under Appendix II of CITES since 2009, and the EU banned exports and imports in 2010.
• Fishing limits: the EU has introduced seasonal closures for eel fishing at sea, and ICES scientists have repeatedly advised that no eels should be caught in any habitat until the stock recovers.
• River restoration: eel passes, ramps and climbing channels are being built at weirs and dams, and old barriers are being removed. On some rivers, silver eels are caught upstream and carried past hydropower plants.

Breeding eels in captivity could one day take pressure off wild stocks, but despite decades of work, scientists have not yet raised European eels through their full life cycle. For now, the eel’s future depends on protecting the young eels described in What are glass eels? and keeping rivers open for the long journey explained in Where do eels come from? Migratory fish such as salmon face similar problems; see Are Atlantic salmon endangered?