frog environmental install revolutionary new eel pass on a canal weir next to Osterley Lock on the Grand Union Canal in Brentford
On behalf of the Zoological Society of London (ZSL) and The Environment Agency, frog environmental has designed a revolutionary new eel pass structure to allow juvenile eels, also known as elvers, to travel through the weir alongside Osterley Lock on the Grand Union Canal in West London.
BBC London reporter Yvonne Hall spoke to ecologist Leela O’Dea.
The new elver pass, which is being installed as part of ZSL’s London-wide European Eel Conservation Programme, aims to make the journey easier for elvers migrating upstream from the Thames, along the Grand Union Canal and into the River Brent just below the Hanwell Lock flight.
Leela O’Dea, Technical Director for frog environmental, explains:
Osterley weir in flood before installation
“This totally new and bespoke structure will be the final piece in the jigsaw enabling more baby eels migrating along the River Thames to reach the freshwater environment of the River Brent, where they can feed and grow to become adult eels. “Sadly the previous eel pass installed two years ago wasn’t strong enough to withstand the force of the water and debris passing over the weir alongside Osterley Lock, the final barrier to overcome on the Grand Union Canal before it connects with the River Brent. “These creatures undertake the most incredible journey in the hope of reaching freshwater where they can thrive and grow, so it’s vital that we enable them to complete the very last section of that journey by installing successful eel passes. “With strength in mind and to avoid a further failure, the inner structure of this new eel pass is made of a single piece of polypropylene, an extremely strong plastic that is both chemically and heat resistant. Reinforced with steel it offers deflection and better protection from trees and other debris moving through the weir.”
Eels spawn in the Sargasso Sea in the western Atlantic and are carried towards European waters by ocean currents. After approximately 1 to 2 years, the young eels arrive in Europe and head up estuaries, including the Thames estuary. They spend up to 20 years in rivers, before migrating back out to sea to breed.
Over the last 30 years the number of elvers joining the adult population of European eels in our rivers has declined.
In 2008 the International Union for Conservation of Nature (IUCN) classified the species as Critically Endangered and in 2005, ZSL set up its European eel monitoring programme to assess the presence of migrating juvenile eels in London, identify restrictions to their movements and gather long term data on elvers entering the River Thames catchment.
Elver pass being installed in weir
“ZSL monitoring since 2006 across the lower Thames catchment has shown the number of young eels arriving into London’s Rivers has dropped by over 90 per cent since the 1980’s. One of the contributory factors causing the decline are barriers that prevent eels migrating upstream and accessing habitat in our rivers. “We hope this new pass over Osterley weir will make a huge difference to eels travelling to the River Brent and we are very grateful to the SITA Trust for funding this work.”On the River Brent ZSL have been working with the Environment Trust and the Canal & River Trust. The Environment Trust set up The River Brent & Grand Union Canal Eel Recovery Programme which has been running for three years, during which four eel passes have been installed at weirs on the River Brent. Since April 2014, almost 63,000 juvenile eels have been recorded in the River Brent by a dedicated team of 20 Citizen Science volunteers led by Chris Cockel of the Environment Trust, Chris adds:
“This data is helping to increase the scientific knowledge of eels, promote their recovery in the waterway system and raise awareness of the importance of canals and rivers as natural habitat. The Environment Trust is continuing to work with ZSL, the Canal & River Trust and other partners to improve the river for eels and other fish.”More information about the eel project…