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Species - European eel

Status

The eel is classified as critically endangered on the IUCN Red List. It is an Appendix II CITES species and a UK Biodiversity Action Plan priority species.

Habitats

European eel (Anguilla anguilla)

The European eel has an interesting life cycle that includes many different processes including the migration from fresh to salt water. It is a catadromous species, which means it migrates to the ocean to breed. The eel faces many problems throughout its life, which greatly impacts on population numbers and its ability to recruit new individuals.

The eel can grow between 60 and 80 centimetres, but it is usually slightly smaller. The average age of an eel is 20 years, but it can vary greatly from 2 to 85 years with females typically being twice the age and size of males. When they are in their adult stage they are generally dark brown, olive green or black displaying a yellow/green belly. They have a long narrow body shape with a longer lower jaw. The skin has a slimy feel with tiny or no scales. They have long continuous dorsal, anal and tail fin.

The life cycle starts with spawning in the Sargasso Sea in the western Atlantic. The various processes of growth and maturity have created individuals names for the eel at each stage. The initial stage is the production of larvae, leptocephalli, which have the appearance of curled leaves and are known to spend up to three years at sea drifting with the plankton. It is thought that the Gulf Stream current carries the larvae to the coasts of Europe where they undergo metamorphosis. At this stage the eel are known as glass eels due to their appearance. They are transparent, but take the appearance of small fully formed eels. As they begin their migration into freshwater in large numbers their colouring becomes darker and they measure about 50 millimetres. At this stage they are called brown or yellow eels. When they reach freshwater the males spend 6 to 12 years and the females spend 9 to 20 years to reach an appropriate level of maturity before returning to the sea. Once they become sexually mature they will then return to the sea displaying a sliver colour and are known as silver eels. The most common time for returning eels to sea is during a dark, moonless and stormy night (It is thought that they are affected by the lunar cycle). Once they return to the sea they spend their time living in muddy, rocky or stony areas hiding under rocks and in crevices.

The eel is found to be distributed in all European rivers which drain into the Mediterranean, Baltic and North Sea; also in south of the Canary Islands in the Atlantic and parts of north Africa and Asia. It is classified as being native to the United Kingdom, but it is also native to other countries as well.

There are currently major concerns about the lack of recruitment to current populations of the European eel. It has been recorded that the eel’s population numbers have been declining since the 1980s. There are various factors which affect the population numbers. Natural predation levels are high and have increased through the introduction of non-native species. Acts of over harvesting have created a severe indent in the current numbers, demands for the species are high in Asia and Europe and the price is increasing for them. The introduction of eels from Japan bought with them a parasite, Anguillicola crassus, which is thought to reduce and impact the ability for the eels to reach breeding grounds therefore reducing their chance to reproduce. Other physical implications have reduced the ability to reach spawning grounds or their chosen freshwater destination.

Hydropower installations can act as a physical barrier, which can stop the eels being able to travel along the river course. There are currently regulations being put in place to reduce the disturbance to eel spawning and increase their population numbers. The European Council (EC) Regulation No 1100/2007 are looking to improve the rivers to allow for an easier journey to the sea.
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