Bristle-bottomed bridges are being fitted to weirs on Cumbrian rivers to enable European eels (Anguilla anguilla) to overcome the final barriers in their mammoth migrations that begin in the Sargasso Sea near Bermuda. Weirs, dams and flood defences on UK rivers are thought to be one of the major reasons for a 95% decline in the number of juvenile eels reaching the UK since the 1980s.
The two specially designed "passes" on weirs on the River Leven will help restore the eels to Windermere, the largest natural lake in England, where they have not been seen in significant numbers for 30 years. The troughs, fitted with bristles to allow the eels to slither up and over the weir, are being built by The South Cumbria Rivers Trust (SCRT) and its partner the Co-operative Group. Additional help is being given by attaching floats to tidal flaps in barriers sited in river estuaries, so they stay open for longer.
The European eel used to be widespread and abundant in British rivers, an important member of the nation's aquatic wildlife and the rural economy. However, their population has plummeted in recent decades. Starting life in the Sargasso Sea, near Bermuda, the European eel follows the Gulf stream across the Atlantic to Europe.
Once they reach coastal waters, they swim through estuaries and up rivers to lakes and wetlands where they settle and grow for up to 20 years. Once fully grown, eels return to the sea before swimming back across the Atlantic to spawn.
"As well as opening up quality habitat for this critically endangered species, an increased influx of juvenile eels will have wide reaching biodiversity benefits because the eel plays a key role in the food chain of other species such as the otter and bittern," said Chris Shearlock, sustainable development manager at The Co-operative Group. "Once complete, we will install monitoring equipment that will enable us to assess the benefit of the pass and quantify the number of eels reintroduced to this prime habitat."
In order to restore dwindling stocks across the EU, every member state has had to develop an eel management plan which reflects the unique life-cycle of the eel. In the UK, the Environment Agency is overseeing plans [pdf] to support the eel, which includes the unblocking of migratory pathways through the use of passes, modifications to water pumps and hydro schemes, the creation of wetland habitat, restocking programmes [pdf] and controls to reduce the number caught by fishing.
The passes on the Leven are two of a series being built on rivers across north-west England. The locations of the other eel passes include Bank End in the Lune Estuary, Lancashire, Eels Dam near Haverthwaite, south Cumbria and Stramongate weir in Kendal, Cumbria.
Pete Evoy, trust manager of the SCRT, said: "Eels should be common in the South Cumbrian rivers and becks but their population has declined fast in recent years. It is imperative that such a stressed population should be able to migrate easily from the sea into our fresh water systems."