European Eel

## About

A yellow European eel.

European eels ***(Anguilla anguilla)*** are a species of eel that inhabit both salt and freshwater environments. European eels have scaly bodies however, they also have a thick layer smooth and slippery skin that coats the scales. This skin will often differ in colour between differently aged individuals, appearing a black or grey in sexually mature eels and more vibrant yellows in maturing eels. A pattern that remains constant in all European eels is the presence of countershading meaning the eels have a darker back and a lighter underbelly, which aids them camouflage with their environment from the perspective of both underwater and airborne predators. The dorsal and anal fins of all freshwater eels are merged, rapping around the tapering tail of the eels and lining the majority of their backs and underbellies. The pectoral fins remain unfused and are located just adjacent to the gill slits. European eels reach 60–80cm (2.0–2.6ft) in length and rarely exceed beyond 1m (3.3ft), reportedly on occasion the eels can reach a massive 1.5m (4.11ft). European eels can also weigh 1-2kg (2.2-4.4lbs).

## Diet

Hunting exclusively at night, European eels will prey on both vertebrates and invertebrates as well as the sunken carrion of deceased creatures. Among the living prey they consume are fish, molluscs, crustaceans and insect larvae. Smaller juvenile eels will generally feed on larvae or slugs while mature individuals prefer larger prey such as freshwater fish.

## Conservation Status

European eels are known as critically endangered by the IUCN and have declined to this state due to a variety of both natural and human threats. Man made barriers obstruct the eel's migration path from the Atlantic, these barriers act as blockades in freshwater industrialised environments making it unintentionally harder for the eels to arrive at their desired destination. Many of these barriers consist of hydropower turbines or pumps along with water management systems which often seriously injure or even kill juvenile eels. A European organisation known as AMBER International specialises in the recording of these barriers and raising conservational awareness about them. 415,000 barriers have been recorded as of 2022 by usage of this tool. As European eels are a migratory species climate change greatly disturbs their lifestyle. Most prominently, climate change manipulates the ocean currents, throwing the eels off their path. Climate change also relates to the hydrological imbalances in the Eel's freshwater habitats, increasing the severity and frequency of droughts. Possibly the most drastic threat towards European eels is the fishing industry. European eels are farmed both sustainably and unsustainably throughout Europe since the late 1800s for food, although exporting eels from the EU has been banned since 2010, large scale export remains consistent. Generally more mature eels are fished much more frequently, leading to a drastically imbalanced population, with fishing of mature individuals decreasing due to scarcity, whether as juvenile eel fishing increasing.

## Range and Population

As European eels are migratory fish, they are found in a vastly diverse array of environments but generally prefer murky freshwater environments, migrating from their Atlantic spawning grounds to Europe and northern Africa. These eels occur as far north as Iceland and Norway and as far South as Morocco and have even been recorded in Pechora river in northwest Russia. Eels specialise in hunting in low visibility environments favouring rivers with a higher concentration of debris and silt, rather than clear rivers. These opaque rivers generally aid in the evasion of eels from predators that seek them out from the sky. The current population of European eels is unknown due to the population rapidly declining due to fishing exploitation ever since the 1960s/70s, as during these years eel exploitation was at an all time high.

## Behaviour

European eels are a migratory species of eel and despite their name, are actually spawned in the Atlantic instead of Europe. Sexually mature European eels or silver eels, will migrate during the months of October and December from European rivers to the Atlantic Sargasso sea. After arriving the silver eels will reproduce, laying their eggs deep in the Sargasso sea, leaving their young to emerge from the eggs during February and May. The hatchlings appear as small leaf-shaped transparent larvae. Eels in their larvae state will travel back to European waters through ocean currents spanning a journey of 6,000km (3,728mi), and once they arrive they will transition into glass eels and eventually darker elvers on entering a freshwater habitat. Elvers will travel upstream, sometimes crossing vertical surfaces and even land just to find an appropriate place to live. Elvers will eventually transfer into much larger yellow eels, male eels can stay in this state for 12 years whether as larger females may stay in this state for upwards of 20. Eventually, yellow eels will finally become silver eels at the age of sexual maturity and make their way back to the Sargasso sea to continue the cycle. During this change silver eels will become more equipped for their journey, by having a reduced stomach and enlarged eyes to better view the deep sea, we are currently unsure as to whether eels die or not after completing this journey.

### Relationship with Humans

European eels are farmed by humans as a food source. Generally wild and farmed European eels will avoid humans due to them being a perceived threat. European eels are extremely skittish fish and being surrounded by large animals such as humans, causes them to become easily stressed and agitated, even using their powerful jaws to bite fine line or even humans in self defense.

## In Captivity

There are currently no captive European eels.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/60344/152845178
* European Eel | Canal & River Trust - https://canalrivertrust.org.uk/enjoy-the-waterways/fishing/caring-for-our-fish/freshwater-fish-species/rare-and-protected-fish/eels
* European Eel | WWT UK - https://www.wwt.org.uk/discover-wetlands/wetland-wildlife/european-eel/
* Amber International - https://amber.international/
* European Eel | Science.org - https://www.science.org/doi/10.1126/sciadv.1501694#:~:text=Adult%20European%20eels%20begin%20their,area%20in%20the%20Sargasso%20Sea.
* The Amazing Life Cycle of the European Eel | ZSL-Zoological Society of London - https://www.youtube.com/watch?v=WBRnNk\_uo9Y