European eel

Eel spend most of thir live in fresh water rivers and ditches. Eels the start and the end of theire lives is in the Sargossa sea, thousends mile from theire freshwater rivers. Like other anguillid eels, European eels have a complex life history, spending most of their life in the “yellow eel” growth phase, during which they inhabit the bottoms of fresh and brackish continental waters. European eels can live more than 50 years in this stage. They are a popular food fish, and have been fished for centuries. But nowadays they are in sharp decline.

Silver Eels in a wood, observed by a Kingfisher.

Live circle eel

The live circle is fascinating and long : long in time, eels easely reach a livespan of 50 years and more. And a long distance: Europe-Sargasso sea is about 5000 kilometers. it all starts as an egg.

Starting live in the Sargasso sea

The spawning grounds must be in the Sargasso Sea, although no one has ever witnessed eels spawning. The Sargasso sea is the deepest part of the Atlantic, between Bermuda and the West Indies. The larvae must feed on microscopic jellyfish and for a lesser part on copepods, both belonging to the zooplankton. This is concluded as the larvae are often infected by parasitic copepods that are part of the zooplankton. (1)The Sargasso sea is covered with floating yellow seaweed, Sargassum natans and Sargassum fluitans. These floating seaweeds give shelter to the first planctonic stages of the eel.

Sargassum weed. This is the weed that covers the Sargasso sea. The small spheres that llok like berries are gas filled, and keeps the weed floating. Between the leaves many animals find shelter or are at the start of there live , for example mahi mahi , sailfish and jacks.

From the sargasso sea the larvae are drifted to the european estuaries.

The larval stage : becoming glasseels

The larvae, known as leptocephali, are subsequently transported back by ocean currents to continental waters, where the juvenile eels, known as glass eels, enter freshwater bodies or settle in coastal marine areas.

The glass eel is, like its name already indicates , almost completely transparant. Only the haunting eyes and a the spine are visible,

The glass eels leave the ocean and swim upstream into the European continent’s rivers. Hiding in the shadows of eelgrass beds, they grow fat and up to five feet long over 20 years or so before heading back to the Sargasso.

European eel in freshwater changes from color and feeding habits.(6). But eel diet is composed almost entirely of bottom-living organisms: fish , insects larvae, worms , and sometimes even worms that lives ont land , like earth worms.

Starting as a glasseel they started to change color, shape and behavior: They develop a pointed teethed mouth, feeding on crab, (3) or broad mouth , feeding on fish.(1), both are called “yellow eels”, but in German (3) is called “Spitzkopfaal”,and (1) is called: “Breitkopfaal” , It takes some 10 years to become an adult or silvereel (2), in German:”Blankaal”, with their flanks silver colored, their bellies white and with a green back. Nocturnal opportunist carnivores, they eat a broad diversity of fish and invertebrates, like crabs , larger fish and frogs and will also scavenge on dead organisms. The silver eels start to swim to the sea and start the big journey back to the Sargasso Sea , only to spawn there. During this period they don’t eat , and live on bodyfat.

Back to the Sargasso sea

It takes one year to swimm back the 5000 kilometers . During the night, they swim in shallow water, at a level between 200m below the surface. In the morning they dive to 1000 meter depth or more, this way avoiding most of the predators.

Spawning in the Sargasso

Spawning must take place at greath depth, although no one has ever witnessed eels spawning. Soon after spawning the eels die.

The European eel is endangered

There has been a sharp decline in the population and the eel may notable to recover unless a long-term, stringent recovery plan is instated.

At this moment (2017) there is no sign of population recovery. The full explanation for the recruitment and population crash of these eels is not fully understood. Heavy, unsustainable fishing of all life stages continues to impact a downward decline of the population. But there are more factors:

The parasite Anguillicola crassus, once introduced by Japanese eels (A. japonica) farmed in Europe in large open pens alongside A. anguilla. is a danger. The habitat of the yellow eels is polluted , and there are many dams, which disrupt migration routes. Climate change effecting spawning areas: because of climate warming there has been a shift of the spawning zone.

In the context of increased temperature fronts between the hot and cold water masses – and hence the spawning areas of eel – have spread further north than seen before, a change that might influence both larval feeding and drift pattern.(2)

Measurements to help the Eel

In 2010 the European Union banned exports of European eels, which had been declared critically endangered, causing a sudden shortage. It was particularly acute in Japan, where people consume more than a hundred thousand tons of unagi a year and hold an annual eel-eating festival, Doyo no ushi no hi, in the height of summer.

Stopping the fishery for wild eel would be more help. Already the production of European eelfarming is twice the fishery catch.

Reference

1 Are eels (Anguilla anguilla sp) planctonic feeders? Evidence from parasite communities C. R. Kennedy, P. Nie, J. Kaspers, J. Paulisse October 1992

2 website CLIMATE CHANGES BEHIND THE DECLINE IN EUROPEAN EEL?

4 painting by

6 painting by Heinrich Harder