European eel
Encyclopedia
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
, a snake-like, catadromous
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
fish. They can reach in exceptional cases a length of 1½ m, but are normally much smaller, about 60–80 cm, and rarely more than 1 m.
Much of the European eel’s life history
Eel life history
The eel is a long, thin bony fish of the order Anguilliformes. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history...
was a mystery for centuries, as fishermen never caught anything they could identify as a young eel. Research in the 19th and 20th centuries shed some light on the subject, though questions remain. They are generally believed to spawn in the Sargasso Sea
Sargasso Sea
The Sargasso Sea is a region in the middle of the North Atlantic Ocean, surrounded by ocean currents. It is bounded on the west by the Gulf Stream; on the north, by the North Atlantic Current; on the east, by the Canary Current; and on the south, by the North Atlantic Equatorial Current. This...
, after which the adult eels die. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e (Leptocephalus
Leptocephalus
A leptocephalus is the flat and transparent larva of the eel, marine eels, and other members of the Superorder Elopomorpha. Fishes with a leptocephalus larva stage include the most familiar eels such as the conger, moray eel, and garden eel, and the freshwater eels of the family Anguillidae, plus...
) drift towards Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
in a three-hundred-day migration (FAO data). When approaching the European coast the larvae metamorphose into a transparent larval stage called "glass eel", and enter estuaries and start migrating upstream. After entering fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
, the glass eels metamorphose into elvers, miniature versions of the adult eels. As the eel grows it becomes known as a "yellow eel" due to the brownish-yellow color of their sides and belly. After 5 - 20 years in freshwater the eels become sexually mature, their eyes grow larger, their flanks become silver and belly white in color. In this stage the eels are known as "silver eels", and they begin their migration back to the Sargasso sea to spawn.
The European Eel is a critically endangered species. Since the 1970s, the numbers of eels reaching Europe is thought to have declined by around 90% (possibly even 98%). Contributing factors include overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
, parasites such as Anguillicola crassus
Anguillicola crassus
Anguillicoloides crassus is a parasitic nematode worm that lives in the swimbladders of eels and appears to spread easily among eel populations after introduction to a body of water. It is considered to be one of the threats to the sustainability of populations of European eel...
, barriers to migration such as hydroelectric
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
plants, and natural changes in the North Atlantic oscillation
North Atlantic oscillation
The North Atlantic oscillation is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the...
, Gulf Stream
Gulf Stream
The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean...
and the North Atlantic drift
North Atlantic Drift
North Atlantic Drift is:* An ocean current that continues from the North Atlantic Current* An album by Ocean Colour Scene: North Atlantic Drift this doesn't make any goddamn sense....
. Recent work suggests that PCB
Polychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...
pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
may be a factor in the decline.
Eels have been important sources of food both as adults (including the famous jellied eels
Jellied eels
Jellied eels is a traditional English dish that originated in the 18th century, primarily in London's East End. The dish consists of chopped eels boiled in a spiced stock that is allowed to cool and set, forming a jelly...
of East London
East End of London
The East End of London, also known simply as the East End, is the area of London, England, United Kingdom, east of the medieval walled City of London and north of the River Thames. Although not defined by universally accepted formal boundaries, the River Lea can be considered another boundary...
) and as glass eels. Glass eel fishing using basket traps has been of significant economic value in many river estuaries on the western seaboard of Europe.
In captivity European eels can become very old.
Decreasing population numbers and breeding projects
For quite some time, the population number of European eels has been falling. For this reason, a research project has been started by Innovatie Netwerk, led by Henk Huizing to see whether it is possible to breed European eels in captivity. The breeding of European eel is very difficult, since eel is generally only able to reproduce after having swum a distance of 6500 kilometers. In the project, this is being similated by means of a hometrainer for the fish. Innovatie Netwerk has also started abreeding project, called InnoFisk Volendam.