European Eel

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The European eel

has, perhaps, one of the most interesting life history patterns of all European freshwater fish. They are widely distributed within European freshwaters and can be found in a wide variety of freshwater and estuarine habitats.

Eel Larvae (leptocephalus)

Juveniles (Silver Eel)

Elver

Photos By .. Ron Offermans, courtesy Wikimedia Commons.

Facts

* Once eels have left the rivers to return to the sea to spawn, they stop feeding, and so have to rely on stored energy alone.

Their body undergoes dramatic changes: the eyes start to enlarge in size, the eye pigments change for optimal vision in dim, blue, clear, ocean light, and the sides of their bodies turn silvery, to create a counter-shading pattern to make them difficult to see by predators during their long open ocean migration.

* Eel migrations are affected by a number of factors. Their movement upstream is mainly triggered by water temperature

* Eels are capable of surviving for periods of time out of water and can cross land and damp meadows in their search for water systems.

* Mature eels prefer to move seawards when it is dark and large migrations are known to occur on wet, stormy autumn nights especially when the half-moon is on the wane.

Are eels under threat

All life stages of the European eel, glass, elver, yellow and silver, have been exploited by man for centuries and throughout Europe they have supported a number of large-scale commercial fisheries. Within Scotland, eels have not been heavily fished, but some limited exploitation has taken place in some localities. Although long-term datasets are few, it is clear that European eel have undergone a significant and drastic decline over the last two decades. It has been estimated that eel numbers have decline by over 90% during this period.

Are there conservation measures in place?

The widespread decline in European eels has led the European Commission has develop an Eel Recovery Plan (Council Regulation No 1100/2007). This plan aims to return the European eel stocks adults and glass eels) to sustainable levels. Each Member State is required to establish national Eel Management Plans. An Eel Management Plan for Scotland was developed by Marine Scotland Science in 2008.

The European eel was also added to the UKBAP Priority Species List in 2007

Conservation status

European eels are commonly fished when then congregate, en masse, as elvers or during their downstream migration as silver eels. They are not listed as being threatened.

Eels are fascinating creatures.  European eels are found in rivers and lakes in most European countries.  Females grow much larger than males and can reach up to 150cm in length.

Although most eels live for less than 20 years, eels as old as 90 years have been found.

Their diet is made up of insects, worms and small fish, and this gives the eels a yellow colouration, and European eels are sometimes called ‘yellow eels’.  

When eels are ready to reproduce (spawn), they start to turn silver in preparation for their migration to their spawning grounds that, based on the size of larval eels discovered in earlier surveys, are thought to be situated in the Sargasso Sea.

Contact R.C.F

What makes the eel life-cycle so interesting?

The migration of eels from the freshwater and estuarine waters of Europe to the Sargasso Sea, located to the south-west of Bermuda, is one of the most impressive feats of animal migration observed in nature. Although this migration is accepted as scientific fact, surprisingly little research has been carried out to determine whether this the only site used by European eels to reproduce. No silver eels, the migratory adult form, have ever been caught in the open ocean, and it is unclear whether spawning takes place at only one time of year or over an extended period. It is also unclear how long it takes eels take to get to their spawning grounds, and how many of the eels that leave Europe reach the Sargasso Sea to spawn.

After spawning, it is assumed that the eggs drift eastwards towards Europe with the Gulf Stream. During this time, the eggs hatch and the young larvae, now called leptocephalus, are 'leaf' shaped and it is only on reaching the European continental shelf that they metamorphose into the cylindrical shape that we associate with eels. These fish are virtually transparent and are called 'glass eels'.

On entering freshwater, the glass eels start to change in colour and become darker as pigmentation takes place. They are now known as elvers. During this time, they migrate upstream and occupy a wide variety of freshwater and estuarine habitats, feeding on invertebrates and fish. Eels are also known to move overland, moving over wet terrain to get to some waterbodies. During their freshwater-resident phase they are known as yellow eels and they can remain in these habitats for more than 20 years. When eels are ready to reproduce, their colouration changes and they start to turn silver in preparation for their migration to the Sargasso Sea.

Elver Migration

Swimming Eel

Large Eel Underwater

The spawning migration of the European eel from rivers and brackish waters in Europe to the Sargasso Sea is one of the most impressive feats of animal migration and orientation, yet it is a mystery that over 2000 years of study has not fully solved.

  No silver eels have ever been caught in the open ocean, and the habitats that eels are thought to use during migration are extremely difficult to sample with traditional equipment.  

Little is known about whether eels travel to one spawning ground, or many, and whether spawning takes place at only one time of year or over an extended period. Added to that, we don’t know the routes eels take to their spawning grounds, what ocean currents they use to ‘hitch a lift’, how long eels take to get to their spawning grounds, and how many of the eels that leave Europe reach their destination to spawn, or how many die on their journey.