Silver Eel

Silver Eel
  • Scientific name: Anguilla anguilla
  • Also know as: European Eel, Common Eel (and at different stages of their life Glass Eels, Elvers, Yellow Eel and Brown Eel)
  • Size: Up to 5ft in length and 20lbs. Shore caught typically 1 – 3lbs.
  • UK minimum size: N/a – all silver eels caught by anglers must be returned to the sea by law (see below).
  • UK record: 11lb 2oz (listed as a freshwater record, see below)
  • IUCN Status: CR (Critically Endangered)
  • Distribution: Once abundant around the UK, Ireland and the rest of Europe. While it is still found across the British Isles numbers are much reduced and silver eels are now absent from areas where they were once common
  • Feeds on: Fish, worms and crustaceans are eaten when it lives in the sea during the silver eel stage of life. Smaller fish, frogs, insect larvae and any other dead and rotting creatures when in its freshwater environment.
  • Description: [When at the Silver Eel stage of life] Long thin body which is covered in slime. Back and flanks are grey to dark green with lower half and belly pale/white. Dorsal fin starts one third along the body and joins the anal fin. Lower jaw protrudes noticeably further than the upper jaw.

Life Cycle

The silver eel is a mysterious creature which has baffled scientists and fishermen alike for centuries. It has taken until the last few decades for scientists and marine biologists to put together an understanding of the life-cycle of this creature, and a number of mysteries remain.

As long ago as 350 BC the Greek philosopher Aristotle could not work out how silver eels reproduced as there did not appear to be any such thing as a baby or immature silver eel. Eventually, he concluded that they simply emerged as fully-grown eels out of the earth itself. Thousands of years later the silver eel was still a mystery to science, and there was a widespread belief that eels were actually a species of worm and not a fish species. The young Sigmund Freud began his scientific career in the 1870s working under the German zoologist Carl Claus. Freud’s work entailed dissecting hundreds of silver eels in an unsuccessful attempt to locate the reproductive organs of the males (silver eels only develop reproductive organs towards the end of their life prior to migrating, meaning Freud had been given a hopeless task).

Aristotle was puzzled by eels in 350 BC. Many centuries on many mysteries about eels life cycle still remain.

At this point it was thought that there were several different species of silver eel. However, in the 1920s the Danish biologist Johannes Schmidt discovered that eels were migrating to the Sargasso Sea. His research is now renowned as key breakthrough in understanding the life cycle of the silver eel. By the 1970s scientific research had finally established that the different eel species were in fact all the silver eel at different stages of its life, and the life cycle of the silver eel was finally understood:

Copyright: lukaves / 123RF Stock Photo
  1. The fully-grown silver eel (aged anywhere between ten and thirty-five years) will stop feeding and the bodies of females will become heavy with eggs. The silver eel will then begin its four thousand mile migration from Europe to the Sargasso Sea, around Cuba, Florida and the Caribbean. Once there the eels will spawn and produce eggs, and soon afterwards the adult eels will die.
  2. The eggs hatch and the larvae begin to drift in the tide.
  3. Once the larva has grown they begin to swim back towards Europe. This journey may take over a year.
  4. Once they are close to the European coast then they being to change into a strange-looking completely transparent immature eel, known as a glass eel. The glass eels enter estuaries and begin migrating into freshwater, travelling upstream into rivers.
  5. Once established in their freshwater habitat they then change into elvers – baby eels.
  6. As elvers grow bigger they take on a yellow to light brown colouration and change shape. During this stage they are known as yellow eels (or less commonly brown eels), and may stay in this stage for years, possibly decades.
  7. Eel on Grass
    A silver eel moving across land.

    At some point the yellow eel will transform into a silver eel and begin to travel to the sea. Silver eels will travel down rivers and, if necessary leave the water and move across land in a manner similar to a snake, making use of ponds and wetlands which are present on their journey. Due to their rigid gill structure, silver eels can survive out of water for several hours, while some accounts state that silver eels can live for up to 48 hours out of water, as long as they are in a damp environment. Eventually, the eels will reach the sea and after spending anything from a few months to several years living there males will begin to develop reproductive organs and females will fill with eggs and then begin the migration to the Sargasso Sea to spawn and begin the life cycle all over again.

Continuing Mysteries

Glass Eel
Clip of an eel migrating when in the glass eel stage of its life. © Kils.

While modern research has revealed much about the silver eel there are still mysteries about this species. It is unknown what triggers the changes between the different stages in the eels development, and it is unknown how the silver eel decides that the time is right to migrate. Furthermore, it is only now that we are beginning to understand how the mature silver eel finds its way to the tropical Sargasso Sea and how the tiny (10mm long) newly hatched elvers migrate to Europe. A 2009 study by Cefas (Centre for Environment, Fisheries and Aquaculture Science) involved satellite tagging silver eels which were then released from the west coast of Ireland. The study found that these eels did not take a direct route to the Sargasso Sea, but instead took a long, circuitous route southwards. It was concluded that the eels were seeking out warmer currents which would help propel them on their journey of several thousand miles. It was also discovered that the silver eels would undertake vertical migrations – swimming fairly near to the surface during the day, but diving down to depths approaching 1000 metres at night and returning to the surface during the day. Since eels do not feed during their migration this behaviour cannot be explained by looking for food and the reason for these deep dives remains unknown.

Further research was carried out at the University of North Carolina in 2017. They found that newly hatched silver eels had an inbuilt ‘magnetic map’ which they used to sense changes in the earth’s magnetic field and navigate from their birthplace in the Sargasso Sea to Europe. It was found that eels also used magnetic fields to locate the Gulf Stream – the warm and fast Atlantic current which pushes northeast from the Gulf of Mexico to European waters. Silver eels effectively hitched a ride on this to preserve energy and make their journey across the Atlantic Ocean faster (although it still takes them almost a year).

Silver Eel as Food and Cultural Significance

Jellied Eel
Jellied eel on sale in a fishmonger.

Eels have been consumed by humans for many centuries. Yellow eels and fully grown silver eels are caught in nets and sold as food, such as the famous jellied eel – a classic English dish associated with the East End of London. As elvers they are caught and the price has risen massively in recent years – restaurants will now pay around £200 for a kilogram of elvers. There is also demand from Asian countries to be supplied with European elvers for fish farms (although they can only be supplied illegally as European Union countries are now banned from exporting European-caught silver eels outside of the EU). In 2019 –2020 prices £1,000 of elvers can be grown into £15,000 of marketable silver eel. However, a licence must be obtained to catch elvers legally.

Eels as food
Eels being smoked at a food market in Berlin, left, and the Japanese dish of kabayaki, right.

Eels are also an important and culturally significant food in many other countries. In many northern European countries smoked eels are seen as a traditional delicacy. In Asian countries eel is used to make the hugely popular dish of kabayaki. This involved gutting and filleting the eel. The flesh is then cut into strips which are soaked in a sweet soy sauce and then grilled. The Japanese eel (Anguilla japonica) is used to make this dish, although imported European Eels are also used.

Silver eels have been caught by humans since the beginning of recorded history, with Britain’s last traditional eel catcher retiring only recently. Fifty-year-old Peter Carter from Norfolk used traditionally made wicker traps to catch eels but announced he was quitting in January 2016, saying he could not make the job pay and had not been able to find a successor. His retirement ended a 3000-year-old practice of catching eels using traditional methods in England.

Ely Eel Day 2007
A parade at the Ely Eel festival in 2007.

The cathedral city of Ely in Cambridgeshire has a long association with eels. The city was originally built on an island surrounded by marshes and fenland meaning that Ely was only accessible by boat until the area was drained in the 1600s. In its early history the economy of Ely was heavily reliant on catching and trading eels. Indeed, the name of the city is derived from its original Anglo Saxon name which was ‘Island of Eels’. The long association between eels and Ely is still celebrated today in the annual Ely Eel Festival which is held in April or May and features parades, music, dancing and traditional eel dishes.

Silver Eel – Now a Critically Endangered Species

Silver eel is currently classed as Critically Endangered by the IUCN (International Union for the Conservation of Nature) meaning they are at imminent risk of extinction and have also been added to Greenpeace’s redlist of endangered species. The IUCN calculates that on a worldwide basis silver eels have reduced in number by around 95% in the last fifty years.

There are a number of reasons for this decline. Commercial harvesting has certainly played a part, and the fact that eels are exploited at every stage of their life makes them more vulnerable than most species to overfishing. As well as this the parasite Anguillicoloides crassus has also had a major impact on eel numbers. This parasite originates from Asia and is thought to have been introduced when Japanese eels (Anguilla japonica) were imported to Europe in the 1980s to be used in aquaculture. The parasite infects the swim bladder of eels and can lead to the rupture of the organ and the death of eel. Anguillicoloides crassus is now thought to be widespread throughout European eel populations. In addition to this building work and developments around rivers such as the creation of hydroelectric plants, dams and flood defences have also hit numbers by blocking the migration paths of eels. Furthermore, natural changes in the Gulf Stream and North Atlantic sea movement may also play a part in disrupting the migration of eels. In 2019 news emerged of another unexpected threat to silver eels in the Thames – high levels of cocaine in the river. Media outlets reported that cocaine was getting into the river through waste water and was making eels “hyperactive” and potentially affecting their muscles and skeletal systems. In 2021 it was reported that a similar issue was found during the Glastonbury Festival. Researchers found that traces of MDMA and cocaine were entering the nearby River Whitelake through people urinating on the ground. Drug traces remain present in urine which ends up in the river, potentially affecting silver eels. It was found that levels of MDMA were over one hundred times greater, and cocaine forty times greater, downstream of Glastonbury in the weeks following the festival.

Recent years have seen a number of different measures taken to try and reverse the decline in eel numbers. In Britain there are large-scale conservation efforts to help eels migrate past the barriers which have been put in place of their migration. In 2014 volunteers help to catch some of the estimated one million elvers in the River Parrett in Dorset and transport them past barriers and then return them to the river. There are also Europe-wide restocking schemes, with a large proportion of the silver eels which are legitimately caught by commercial fishermen having to be used to restock eel populations in areas where eels are low in number. Anglers have also been banned from retaining any silver eels they catch and must return this species to the water if they are caught (see below) in an attempt to protect numbers.

Illegal Trade in European Eels

European silver eels are in such demand in Asia (where they are seen as a delicacy) that huge sums of money can be made by exporting this species to China, Hong Kong, South Korea and Japan. The trade in silver eels has been referred to as “the largest wildlife crime on earth” and is believed to be worth around £3 billion each year, making it more lucrative than trafficking drugs such as cocaine.

Europol Headquarters
Europol headquarters in the Hague.

The trafficking of silver eels is, belatedly, being taken seriously as a crime by governments and police forces across Europe. Europol – the law enforcement agency of the European Union – has launched operations to catch people illegally trading silver eels, and it is now an offence to export European eels out of the EU. There have been numerous examples of people being caught and prosecuted for catching silver eels illegally of attempting to smuggle silver eels out of the UK. In March 2017 67-year-old Gilbert Khoo was caught by Border Force officers at Heathrow airport attempting to export 200kg of glass eels out of the UK. The eels were concealed in legitimate shipments of fresh fish. In 2020 he was given a suspended sentence and 240 hours of unpaid work. The court was told that he had made sixteen shipments of eels from the UK to Asia between 2015 and 2017 which could have had a total value of more than £53 million. In 2021 a man was fined for unlawful fishing for eels on the River Severn. Philip Croker was fined £300 with a £30 victim surcharge for “unlawfully luring elvers – baby eels – towards his net” according to the BBC, but was also ordered to pay the Environment Agency’s legal costs of £10,425. Read much more on this topic in our full article on the illegal trade in silver eels by clicking here.

Methods and Techniques to Catch Silver Eel

Silver Eel
A silver eel photographed making its migration from freshwater to the sea.

Silver eel are caught by anglers in rivers, estuaries and beaches near to freshwater rivers. They will take a variety of different baits such as ragworm, mackerel, herring and sprat, although peeler crab is the bait that accounts for the most silver eels. With so many baits taken it is impossible for anglers to avoid catching silver eels if they are present in the area where they are fishing. When silver eels are caught they will spin and twist in an attempt to escape and will inevitably tangle up the rig and line. The thick slime that covers the eel also makes it difficult to hold to remove the hook. Some anglers wrap the eel in a towel or cloth, as this will allow it to be gripped more securely, but it is thought this removes the protective slime around the eel which it needs to survive. There is an urban myth that a rig should always be changed after catching an eel as the slime on the line will put off other fish, although there is little evidence to back this up.

Bans and Limits on Anglers Catching Silver Eels

In 2010-11 there were bans on fishing for silver eels and anglers catching them were legally compelled to return any caught silver eels to the sea. Ignoring this ban could lead to a fine of up to £50,000 from the Environment Agency. Anglers have been prosecuted and fined for catching silver eels with a rod and line. Local and regional bans are still in place in many parts of the UK. All responsible anglers return silver eels due to the fact this species is at a real risk of extinction unless fishing pressure (from both commercial and recreational fishing) is reduced and numbers are allowed time to rebuild. Remember, silver eels swim to the Caribbean to spawn there and then die so any silver eel caught in UK waters cannot have reproduced. The previous 38cm/14inch minimum size for retaining silver eels has been suspended as all silver eels caught should be returned. The BRFC (British Record Fish Committee) will also reject any silver eels submitted as a new British record due to the endangered status of this species. Interestingly, the rod caught record for a silver eel is listed as a freshwater record (rather than as a shore caught record) as the 11lb 2oz eel which set the record was caught in freshwater at Kingfisher Lake in Hampshire in 1978. Silver eels are sometimes confused with small conger eels, but the main differences are pointed out in this identification guide.