European Eel

Long Journey
The European eel starts life in the Sargasso Sea, in the Northern Atlantic Ocean. The leaf shaped larvae, known as leptocephalii, ride on the currents of the Gulf Stream and North Atlantic Drift towards Europe and North Africa. When they reach European shores, they metamorphose into the transparent glass eels that resemble the eel shape we know. As they move further inshore, and ride the tides up estuaries and tidal rivers, the freshwater mix triggers pigmentation and at this stage they are called elvers. 

They spend many years in this environment, either hugging the coastline of estuaries or moving into freshwater, where they turn a yellow colour, gain body weight and grow in length. The carnivorous European eel tends to feed at night, and is partial to fish and invertebrates. During winter months they may become inactive if the temperatures are low. Growth is determined by several factors, including availability of food, average ambient temperature and stock density. The eel is predated upon by birds, and is a favourite food of grey heron, bittern and cormorants, as well as the otter. 

As an eel reaches maturity, the eyes become bigger, the head broader, fat content increases, the undersides of the skin turn silver or bronze and it becomes known as a ‘silver eel’. These changes prepare it for its journey back to the sea. 

When the conditions are right, eels make their way downriver and back to their breeding grounds. It’s thought that eels favour dark, moonless and stormy nights for their migration back to the ocean. Once at sea, eels live in mud, crevices, and under stones. Spawning occurs during winter and early spring back in the Sargasso Sea. There is currently very little scientific knowledge about this species, so not much is known about their migration back to the North Atlantic. 

Declined
We cannot be sure of the exact reasons behind this dramatic decrease but there are a number of factors that are thought to have contributed. Global warming has caused long-term changes; alterations in oceanic currents and climatic conditions may prevent the eels reaching certain catchments. They could also be suffering from parasites, pollution, barriers to migration (like weirs and hydroelectric plants), and a loss of freshwater habitat or over-fishing. The eel fishing industry is the most valuable commercial inland fishing industry in Europe providing an income for over 25,000 people, but now it is feared that there could be no adult eels left within 20 years if no action is taken. 

The European eel has recently been made a UKBAP priority species due to concerns over its decline and has been listed on CITES (Convention on International Trade in Endangered Species). The UK Eel Conservation Group (including DEFRA, EA, ZSL, academic institutions and stakeholders) meets regularly to inform decisions being made within the EU. 

Appearance and confusing species
The European eel has a number of different stages in its lifecycle which can make it more difficult to identify. You are most likely to see adults swimming in rivers as they make their way back to the sea but you should also look out for elvers which can be found around the coastline and in estuaries moving into freshwater, where they turn a yellow colour, gain body weight and grow in length.