Eel

Statistics

Scientific Name: Anguilla anguilla

Length: average 30cm males and 45 cm females (very large eels can be over 1m)

Weight: 0.5-5 kg

Average Lifespan: 5-20 years to reach maturity

Conservation status

Eels are listed as Critically Endangered on the global IUCN Red List of Threatened Species. They are also a priority species under the UK Post-2010 Biodiversity Framework

When to see

Glass eels and elvers can be seen around spring. Yellow eels can be seen all year but they do become less active in colder months. Silver eels can be seen in winter months upon the start of their seaward migration.

Habitat

Eels are a catadromous freshwater fish meaning they live in freshwater and spawn the sea. Spawning takes place in the Sargasso Sea but the exact location has never been found. Eel arrive en masse somewhere under the dense sargassum weed that floats above them and after this 4000 mile migration from Europe they spawn and die. Fertile eggs float on oceanic current before hatching into leptocephali. These transparent willow shaped larva continue using currents on a long journey back to Europe. This can take up to two years and over this period a transformation takes place to the body of the young eel. The willow shape flattens dorsally, creating a cylindrical body that is known as the glass eel stage. Upon arriving at the coastline the glass eels use tides to carry themselves upstream. Upon entering fresh/brackish waters the glass eels start to pigment and become elvers. At around 8cm these young eels migrate upstream looking for habitat to grow and thrive in. The freshwater stage of the eel, known as the yellow eel, is the longest period of an eel’s life and ranges from 7-20 years dependent on sex, resources and temperature. Upon reaching adequate size and adequate fat stores the yellow eel transforms once again for the final stage of its life. This final stage is know as the silver eel. This impressive metamorphosis sees the animal change colour, pectoral fins widen, digestive tract shut down, eyes grow up to 10 times their original size and muscle mass increase. All of these changes aid the eel on its journey back to the Sargasso sea to start the cycle again.   

How to identify

Eels range in colour usually from olive green to brown, but this is largely dependent on their environment. The elongated shape of the eel makes them easily differentiated from most other fish. Their scales cannot be easily seen as they are deeply embedded in the skin with a thick slime layer that makes them difficult to hold. The different life stages of the eel have historically made identification difficult. Early naturalists categorised the first stages of the eel as a different species. 

Eels in your Local River

The Riverlife Almond and Avon project aims to remove barriers and restore habitat on the river Almond and the river Avon. This will aid fish migration and reproduction. The European eel will benefit by being able to access quality upstream habitat to complete the adult stage of their life cycle.

The Riverlife project runs a volunteer electrofishing training program. This involves volunteers in the monitoring of freshwater species present at sites along the Almond and Avon rivers. This provides  the opportunity to encounter the elusive eel. If you’re interested get, in touch.

Have you spotted an eel in your local river? We want to hear from you!  If you have, then send your photos or stories to us at riverlife@forthriverstrust.org.