Eels are mysterious creatures. For centuries, fishermen couldn’t account for where they came from, as they never caught anything resembling a young eel.
But it is now known that this is for good reason: mature European eels leave their freshwater habitats across the continent, and swim west to an area of the Atlantic ocean on the US coast known as the Sargasso Sea, where they spawn.
Over the course of almost a year – around 300 days, depending on currents – the larvae drift back towards Europe, and before entering rivers and estuaries, metamorphose into clear “glass eels”, before eventually maturing and living in their freshwater habitats for decades.
But in the modern era, eels’ unique life cycle puts them at considerable risk. Habitat loss, man-made obstacles, such as dams, weirs and other infrastructure impedes their migration and impacts their numbers, while disease and the climate crisis are also having an adverse effect on populations.
Overall, the number of eels arriving in Europe has collapsed by 95 per cent in just the last 40 years.
In the UK one project aims to help preserve what is left of the eel population.
The species should now be able to move freely along the River Hull following the completion of a purpose-made “eel pass” at a weir at Tophill Low nature reserve, in East Yorkshire.
The pass, which is a kind of bridge made specifically for eels, is made from an aluminium channel and lined with material to help the fish rise above the obstruction, and will help the eels complete their essential migration.
Dr Ben Gillespie, a river resilience specialist at Yorkshire Water, which worked with the Environment Agency, JBA Consulting and Ward and Burke Construction on the joint venture, said: “These creatures have an incredible life cycle - starting off the coast of America, before travelling across the ocean to Europe, where they can spend a number of years, and then making the return journey to spawn.
“Sadly, they are critically endangered but we know there is a population in the River Hull and, by constructing this pumped eel pass at Tophill Low, they will be able to access the upper reaches to feed once more before making their journey back across the Atlantic.”
Pat O’Brien, fisheries specialist at the Environment Agency in East Yorkshire, said the tidal location had presented “a few design challenges” but the river now has a “really good” fish pass solution that will benefit all migratory fish.
He said: “The weir at Tophill Low, also known as Hempholme Weir, is the tidal limit on the River Hull and so very high priority for fish passage, being essentially the front door to the whole river upstream.”
Additional reporting by PA