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 shore caught record: 11lb 2oz
  • 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.

Silver Eel Life Cycle

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. In the end he theorised 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 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). 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:

  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.
  2. Once there the eels will spawn, and soon afterwards the adult eels will die.
  3. The eggs hatch and the larvae begin to drift in the tide.
  4. Once the larva have grown they begin to swim back towards Europe. This journey may take up to three years.
  5. 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.
  6. Once established in their freshwater habitat they then change into elvers – baby eels.
  7. 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.
  8. 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 over 12 hours, while some accounts state that silver eels can live for up to 48 hours out of water. 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 also unknown how the mature silver eel finds its way to the tropical Sargasso Sea, or how the tiny (10mm long) newly hatched elvers know how to migrate to Europe. A 2009 study by Cefas (Centre for Environment, Fisheries and Aquaculture Science) involved satellite tagging silver eels which 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, indirect 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 carried out by Cefas was released in 2016. Scientists tagged and tracked hundreds of eels from five different locations in Europe and studied how and when the arrived at the Sargasso Sea. It was found that the arrival of eels at the Sargasso Sea was staggered over a long period, meaning spawning took place over a much longer period of time than previously thought. Some eels arrived in the Sargasso Sea and then waited until the following year before spawning. Research into the life cycle of the silver eel continues and there are still many aspects of its life which science has yet to understand.

Silver Eel as Food

Jellied Eel

Jellied eel on sale in a fishmongers.

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 silver eels outside of the EU). At current 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.

Silver Eel – Now a Critically Endangered Species

Silver eel are 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 90 to 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.

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 have also been fishing bans for anglers (see below) and, as mentioned, it is now illegal for European Union countries to export silver eels outside of the EU (although they can be freely traded within the EU). However, there is believed to be a large-scale illegal trade in silver eels, with The Guardian reporting in February 2016 that around twenty tons of European glass eels arrived at fish farms in Asia (despite the ban), meaning that illegal and unreported trading of eels is thriving on a Europe-wide basis, undermining attempts to allow this species to recover.

The potential recovery of silver eels has come too late for Britain’s last traditional eel fisherman. 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.

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 no 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 successfully prosecuted and fined for catching silver eels with a rod and line. Local and regional bans are still be 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 stocks 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. Silver eels are sometimes confused with small conger eels, but the main differences are pointed out in this identification guide.

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