Many species of migratory fish are under considerable threat with data indicating that the European eel (Anguilla anguilla) which has undergone a massive decline in recent years is currently outside safe biological limits. The number of elvers being able to utilise freshwater ecosystems across Europe, once so prolific, have now decreased dramatically.
In the Don Catchment some of the best habitat such as wetland adjacent to the river network, is inaccessible due to the impoundment of the river by weirs which prevent eels and fish from ascending them.
To enable the recovery of the eel stock, the EU has adopted a Council Regulation (No. 1100/2007/EC) which requires member states to develop national Eel Management Plans. This Regulation has been transposed in to UK law through The Eels (England & Wales) Regulations 2009.
The European eel has one of the most fascinating life-cycles on earth. Beginning life as larvae in the Sargasso sea, they make an amazing trans-Atlantic migration to the freshwater rivers of Europe, where they feed before returning again to the sea to reproduce.
Eels undergo several changes in body shape, known as metamorphoses. They begin life as transparent, leaf-shaped larvae known as leptocephali which drift easily in the ocean currents. Once in coastal waters, they slim and become tiny, transparent eels known as glass eels or elvers, en masse, they move upstream climbing waterfalls and rock faces to get into the river system. They spend most of their lives in freshwater where they feed and are solitary, largely nocturnal fish that spend much of their time under rocks or in crevices.
During their time in freshwater, they are known to fishermen as ‘yellow eels’ because of their brown coloration and yellow bellies. Eels are highly dependent on environmental conditions such as temperature, tides and lunar phases. Many stages of their life-cycle occur during specific seasons and at particular stages in the lunar cycle.
As yellow eels, they can remain in freshwater for over 20 (and up to 40) years, before a final metamorphosis occurs; their scales change in texture and colour, becoming coppery or silver and their eyes enlarge and then on dark autumn nights, they migrate downstream and begin their long trans-Atlantic migration back to the spawning grounds. Their urge to migrate is so strong that they sometimes leave the water and slither over the land. During this journey, they cease to feed and their bodies concentrate entirely on producing eggs and sperm for reproduction. By the time they reach the spawning ground, the female eels are heavy with eggs. They produce small, buoyant eggs around 1mm in size, which are scattered in the water column.
They can survive in almost any type of water, including salt, fresh, still or flowing. They are also able to travel over land. They live on the bottom of the water, under stones and in mud and crevices.
Eels mainly feed on invertebrates, such as insect larvae, although they will also feed on small fish. When travelling over land, they sometimes feed on earthworms.
Some interesting facts
• The Victorians believed that they were spontaneously created;
• There is a Greek God in the shape of an eel;
• Pliny, the Roman historian and naturalist, thought elvers grew from horsehairs that were accidentally dropped into the water.
Links to eel related webpages