Fish Guidance Systems

Atlantic currents key to solving eel decline mystery

New studies into wind-driven Atlantic currents are helping scientists in an effort to solve the mysterious decline in the eel population. It is generally accepted that European eels - Anguilla anguilla are born in the Sargasso Sea near Bermuda, migrating to Europe where they spend most of their lives.

Carried by the Gulf Stream, they end up in European rivers where they can spend up to 20 years until embarking on a return journey to spawn.

But unexplained fluctuations in the numbers of eels making the crossing of the Atlantic have hampered the efforts to save the species.

Scientists have managed to make simulations of the eel's journeys on a mass scale by the use of a computer model that followed 8 million minute drifting particles representing the eel larvae, simulating the period between 1960 and 2005.

The results have shown the numbers were big during periods when currents were favourable for a short trip, but when there was a change in the current, journeys were much longer and consequently fewer elvers survived.

Dr Christophe Elzaguirre from Queen Mary, University of London, explained - "There is a clear link. If the weather changes then there is a clear risk for the eel population".
Destruction of river habitats and infections from parasites have also had an impact on the eel population. The researchers say that they need to know the scale of returning young to enable them to save the endangered species. Looking at the currents can help scientists to predict the number of eels successfully arriving on the European coast providing time to adjust management programmes.

Halting the decline
Although the population of European eels has suffered a major decline over the last four decades and are now classified as critically endangered, there are signs now that this decline has been halted. Measures to improve future eel stocks include the provision of eel screens or behavioural barriers at water offtakes, together with elver and eel passes at weirs, sluice gates and other obstructions upstream.

Within Europe, the European Community requires member states to improve the escapement of adult silver eels to sea. FGS is able to provide and install a range of technical solutions to enhance upstream eel passage, including bristle passes and moulded plastic substrates and pumped systems to provide elevated weir crests.

More than 1 million young eels have been released into UK waterways during the last year, more than at any time before. About three-quarters of the juvenile eels were released almost immediately upstream, having been carried upstream past barriers blocking their passage inland.