“Never has an animal been studied for so 
 long and eaten in such quantities, yet 
 remained so little known.” 
 – Richard Schweid, Consider the Eel

European eels are elongated fish with a remarkable life cycle, which involves a 6,000 km migration from the Sargasso Sea where they are believed to spawn, toward the rivers of Europe and back again. They are currently listed as critically endangered.


They have strong jaws and slippery snakelike bodies, and are one of approximately 400 species of eel in the world. Their bodies are covered with slime, which scientists believe helps protect them from disease, escape predators, and regulate the water content in their body in relation to the fresh or salt water around them.


When they are not migrating, European eels generally choose to spend their lives in coastal, estuarine or river habitats on a diet of fish and invertebrates. Animals such as otter and herons can often be seen eating eels but they are sought out as prey by a wide variety of  mammals, birds and fishes, and have been eaten by humans for thousands of years.


Traveller and chronicler Herodotus reported that Egyptians revered eels as a
minor deity.

Humans have eaten eels for thousands of years. The first evidence of
humans eating eels (fish spears and eel traps), found in Mount Sandel,
Northern Ireland, dates from this time.

Eels once shared the same seas and rivers with dinosaurs. The earliest eel
fossils, found in Lebanon, date from the Cretaceous period.

Oppian, in the second century in Sicily, theorised wrongly that eels mated
with snakes, and following the union, eels returned to the sea and snakes
returned to land.

Aristotle is the first to record his theories about where eels come from,
suggesting that they are generated from the mud. He wrote: “Eels are derived
from the so-called 'earth's guts' that grow spontaneously in mud and in
humid ground.”

Dr William Roots calculates that in one minute, 1600-1800 elvers were
passing a given point in the river on their migration.

Eels were a popular food, and almost 2 million pounds of eels were sold at Billingsgate market in London. This was a decrease from the late 1700s,
when it is estimated that over 3.5 million pounds of eels were sold at

As a young medical student, Sigmund Freud was given the task of dissecting
400 eels in his search for their testes. He failed in his search, but moved onto
other endeavors.

Lady Colin Campbell observed that eel fisheries were greatly improved by
hanging plaited grass or hay over obstructions in rivers – a precursor to
eel passes.

Giovanni Battista Grassi and Salvatore Calandruccio prove that the small
marine fish then known as Leptocephalus brevirostris, which resembled a transparent leaf, was in fact the larvae of the European eel and not a different species. This discovery led to the acceptance that eels found in freshwater
begin their lives in the ocean.

Johannes Schmidt begins the task of searching for eels’ spawning grounds, combing much of the Northern Atlantic before settling on the Sargasso Sea
in 1924.

European eel classified as “critically endangered”

Åle, reputed to be the world’s oldest known eel at the age of 155, dies at the
bottom of his well in a Swedish fishing town. A local boy dropped him into
the well in 1859 to keep it clear of insects. The oldest eel to die in an aquarium
– known as Pute – lived to 85.

 100 MYA  6000 BC  1832 AD  1852 AD  1877 AD  1886 AD  1897 AD  1904 AD  2007 AD  2014 AD  450 BC  350 BC  200 AD
  • The Romans kept eels as pets, adorning them with piercings and jewellery. Plutarch even reported that one of these eels, belonging to “the Roman Crassus,” would respond to her master’s voice, and the master went into mourning when she died.
  • Eels can rotate their bodies at 14 rotations per second. The world record for fastest spin by a human figure skater is just over 5 rotations per second.
  • A common child’s tale held that horse hairs put into water would turn into elvers. Lady Colin Campbell recalls having bottles in her nursery “in which the propagation of eels from horse-hair was carried on with the profound faith of childhood”

The European eel is listed as critically endangered on the IUCN Red List. Studies across the European
eels’ range indicate that current numbers of glass eels arriving each year are around 90% lower than they were in the 1980s. This sustained decline is having a negative impact on population levels, as annual recruitment cannot compensate for current rates of loss.

European eels are currently facing a number of major threats:

Climate change and alterations in ocean current may also cause decreases in larval transport and therefore a reduction in the numbers of glass eels arriving along the European coast

There are over 24,000 hydropower plants in Europe. Their turbines can cause increased mortality, particularly to silver eels on their outward migration.

Over exploitation and illegal fishing are causing declines in eel numbers at all life stages.
It is worth noting that all eels sold for food are wild caught, and there is no such thing as ‘farmed eel.’

A number of pollutants have been found to impact the immune, reproductive, nervous and endocrine systems of European eels.

The invasive parasite Anguillicola crassus has become widespread across European waters. This infects the swimmbladder of European eels and is thought to affect their spawning migration.

Freshwater habitats have declined greatly across Europe with 50% of wetlands disappearing within the last century. These ecosystems are vital for the growth life cycle stage of the European eel.

Flood defence engineering and weir construction have created a number of barriers that prevent eels moving upstream. Major rivers across Europe have been cut off to the European eel and therefore
the available habitat in which they can grow has been
greatly reduced.


Since spring 2005, ZSL has been working to conserve these iconic London inhabitants as part of our Tidal Thames Conservation Project. Most of our research is focused on the upstream elver (young eels) migration and what has driven the decline in elver recruitment over the past 25-30 years.

Thames elver monitoring

Throughout the summer for the last 10 years, the ZSL team has circumnavigated London to monitor eel populations twice a week at 4 sites.


Citizen science

ZSL began a citizen science programme in 2011 to expand our monitoring capacity with 11 sites. Monitoring starts in April and finishes at the end of September. ZSL now works with fourteen various partnership organisations and, to date, has trained over 350trained hundreds of volunteers to become eel monitoring citizen scientists. We are always looking for new volunteers and new partner organisations to join this project. If you would like to help please contact:


Monitoring Marshlands

Marshlands are thought to be important habitats, where eels can spend up to thirty years feeding and growing before returning to the Sargasso Sea. ZSL works closely with the Environment Agency to assess resident eel populations
in marshland, and in June 2014, ZSL conservationists began working on a tagging project to assess how eels use
these wetlands.


Breaking down barriers

Removing barriers to elver migration will allow elvers back into rivers where barriers have hitherto stopped their natural migration. This will not only help eels but also add to the richness of our rivers, support predators that feed on eels, and contribute to connections within the wider landscape. ZSL will build four passes on three rivers in London to open up an extensive area of freshwater habitat.



ZSL works closely with the Environment Agency to develop and deliver the eel management plan for the Thames region. The management plan outlines key targets and measures to improve the population and conservation of the European eel. ZSL is also one of the key organisations involved in the Sustainable Eel Group (SEG) which is a made up of scientists, conservationists, policymakers and commercial sectors to support the recovery of the European eel.


Eel monitoring report

ZSL has produced a report looking at the population trends and insights revealed by our European eel monitoring and citizen science projects. Download the full report (PDF, 974KB)


Consider the Eel by Richard Schweid,

Eels by Richard Sweid,

Eel by James Prosek,

A Book of the Running Brook and of Still Waters by Lady Colin Campbell,

Eels and their Utilisation by Perry J. Lane,

The Ocean of Life by Callum Roberts