The European Eel Anguilla anguilla
The European eel, Anguilla anguilla (L) is a native fish of Western Europe, the Middle East and North Africa. It is widely distributed in freshwater and brackish water environments, and occasionally occurs at marine sites. Its range extends from the Canary Islands and Morocco in the south-west to Iceland in the North. It is found throughout the Mediterranean Sea and its distribution extends west to the Azores.
The European Eel is a unique indicator of the environmental health and integrity of our oceans, estuaries and freshwaters
The European eel is a member of the genus Anguilla, a member of the order Apodes and the only genus in the freshwater family Anguillidae which includes 16 species, all but two of which occur in the Indo-Pacific regions of the world. It is closely related and almost identical in appearance to the North American eel, Anguilla rostrata Le Suer. The life cycle of the European eel has only been understood in relatively recent times, and recent advances in our understanding of this matter continue to be made. The European eel is now known to exhibit a catadromous life history, reproducing in the Sargasso Sea, but feeding and growing in European brackish or fresh waters. The larval stage of the eel is called a leptocephalus. Eel larvae are carried by Ocean currents from the spawning grounds in the Sargasso Sea to the European/North African coast. The leptocephali increase in size as they undergo their transoceanic migration reaching approximately 45mm as they approach the coast of Europe.
Progression of glass eels through estuaries is thought to involve active tidal stream transport mechanisms with glass eels swimming in the upper layers during flood tide and keeping to the bottom during ebb tide.On entry into estuarine waters glass eels undergo several stages of pigmentation after which they are called elvers.The temporal extent of the eel?s freshwater life cycle phases varies greatly throughout the range of the species. Growth is affected by water temperature and in northern waters eels tend to be much slower growing and older than those in the warmer waters of more southern regions. The female sex is heterogametic and although male and female eels can live together there is often a preponderance of one sex over the other. Where densities of eels are high (i.e. in the lower reaches of a river), males are often dominant. However, females often dominate lower density stocks deeper in the catchment. Towards the end of the feeding phase of the lifecycle, yellow eels mature and change into silver eels and commence the downstream and transoceanic, migratory phase in the eel life cycle. Male silver eels are smaller, and generally younger, than female silver eels.
In recent times, European eel stocks have undergone a dramatic decline throughout the range of the species and they are now an endangered species. The European Eel is a unique indicator of the environmental health and integrity of our oceans, estuaries and freshwaters, and its recent decline is seen as a serious environmental matter. In response to the decline in eel populations European Council Regulation 1100/2007 “Establishing measures for the recovery of the stock of European eel” has now been adopted in member states.
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Also, make sure to have a look at my PhD thesis which can be downloaded from here: Biology and Management of European Eel (Anguilla anguilla, L) in the Shannon Estuary, Ireland. This is one of the largest studies on European eels to have been ever undertaken in Ireland.