Wednesday Wisdom

The mystery of the eel – from the womb of mother earth and back to the Sargasso Sea
9 November 2011

Take a look at the picture here, and you may think we taken a photograph of a bicycle tire or a snake. But the eel is indeed a fish. Actually, it is one of the most widespread animals in the world: It’s practically found in in every coastal and inland body of water in Europe as well, as along the Mediterranean coast of Africa and Asia. At least for now. Sadly, the eel has become a very rare species and is considered to be threatened throughout its range. Our photographer was quite lucky to see one hiding in the bottom of Öresund, Sweden during our research expedition in the spring 2011.

Eel in Öresund, Sweden, May 2011

A long life of mysteries
There are more than 400 different kinds of eel. The one we know from the Baltic Sea is called the European Eel (Anguilla anguilla). The interesting life cycle of the eel is still a mystery to scientist. Aristotle believed that the eel spontaneously appeared in the sludge as it is “born” out of the intestine of the earth. And the Roman philosopher Plinius writes that the juvenile eel is created from the skin cells of the adult eel. Still nobody knows exactly where it spawns but in 1922 the Danish scientist Johannes Schmidt discovered that eels start their life in the Sargasso Sea, south of Bermuda. Eel begin life a transparent larvae called leptocephalus which means slim head. Already in this state the eel is able swim backwards and forwards. The larvae-stage can last from 3-12 month. During this period, the larvae drift with the Gulf Stream several thousand kilometers northeast arriving in early winter to Southern Europe and in spring to Northern Europe.

Transformations of the eel
Nobody knows how the eels find their home rivers with such accuracy, but when they do, the larvae develop into what we know as glass eels, which is a juvenile eel. The glass eels then swim towards the rivers where they move upstream and migrate into inland waters. Many of them are caught by fishermen on the way. In fact only a small percentage of glass eels actually make it to the rivers. The ones who do survive then transform into what we know as yellow eels. If they are not caught the yellow eels can live in the rivers up to 20 years as predators. It attacks by ambushing its victims by hiding in the sand or mud at the bottom. The adult male eel is about 40 centimeters long and the female can grow up to around 80 centimeters long. The largest eel ever measured was 133 centimeters, and the oldest eel found had the remarkable age of 84 years!After a period in the rivers of Europe, the eel becomes sexually mature and then goes through a final change into the silver eel. Then it starts the long 7000 kilometers swim across the Atlantic back to the Sargasso Sea to spawn. During this journey, the eel does not eat at all. If it is not caught during the trip, either by fishermen or larger fish, the eel spawn when it arrives. After spawning the eel dies.

A threatened species
The long period in the river seems to cause problems for the eel. Not only can eels not It reproduce here, but furthermore, for many years it was considered to belong to inland fisheries. For this reason, ICES was not involved with it. This situation has not changed. The percentage of new glass eels entering the rivers has dropped to 1 percent of what it was in the beginning of the 1980s. And this massive decline is continuing. According to HELOM, the European eel is critically endangered and in risk of being extinct within two generations; therefore,  it is a HELCOM high priority species. In the Baltic Sea, eel stocks are about to collapse. The dramatic decline is a huge problem as the eel is a keystone species in the Baltic Sea and several birds use eels as a food source. In 2007, The EU Council of Ministers set the target that 40 percent of the Silver eel should return to the Sargasso Sea allowing it to contribute to regeneration. However ICES’ evaluation of the eel management plans shows that Sweden and Denmark are not likely to meet the target of enabling 40 percent of the stock to spawn this year. In the Baltic Sea eel also is endangered by IUU fishing. There are strong scientific arguments for the suspension of all ell fisheries. Oceana campaigns for meaningful long term management plans for eels in the Baltic Sea.