Where have the eels gone

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Keskiviikko 18.1.2023 klo 14:51 - Mikko Nikinmaa


Everything was better in the past. That is the slogan of conservative populists throughout the world. It is actually true for some things, but the actions should be completely different from the ones advocated by the populists in order for us getting the good things from the past also in the future.

Here I am focussing on the eel. Smoked eel is a true delicacy. When I was a child, one got eels virtually every time one went fishing. The fish was fatty and had virtually no bones making it tasty and easy to eat. However, eels started disappearing from the shops and waters from 1970’s onwards and now you can rarely find them anywhere.

The life cycle of the eel is the main reason why the species is so vulnerable to environmental contamination. The European eel stocks have decreased more than 90 % from 1970’s to 2010’s. If one starts from the sexually mature eel, it migrates several thousand kilometres from the inland waters, where it matures, to the spawning site in Sargasso Sea. During this months-long migration the fish does not eat, but uses the fat deposits as energy stores. This fact has several consequences. First, the condition of eels reaching the spawning site is poor. Many do not make it to the site at all, and the rest are barely able to make the final effort of the spawning migration. Any lipid-soluble environmental contaminants are released to the circulation when lipid deposits are used for energy production. This further weakens the fish. Also, because of the climate change, the ocean currents may have weakened causing an increase in the energy consumption during swimming from Europe to Sargasso Sea. This also weakens the eel before spawning.

The adult eels die after spawning, but the developed embryos start their long travel towards the European feeding grounds. No specific problems have been found in the early part of the migration in the Atlantic. However, it is possible that the food items of the eel embryos have decreased in abundance and that ocean currents have slowed down. When the eels come to the European coasts, a final strenuous part of the travel awaits. They must go up to suitable growth sites. In selecting where to swim to, eels use, e.g., the lateral line organ. This sensory organ is very sensitive to metal contamination. Thus, the present increases of copper, lead and cadmium levels may disturb the final leg of eel migration.

In short, eels suffer from environmental contamination in most parts of their migration. Further, the studies have shown that the presently occurring contaminant levels are adequate to cause, e.g., sensory problems. Consequently, to be able to go back to the good old days, when smoked eel was a common delicacy, we need to improve water quality.

Avainsanat: aquatic toxicology, metal pollution, climate change


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