Endangered Thames eels to benefit from latest science

Critically endangered eels in the Thames will benefit from new research that sheds light on how the creatures navigate the waters to swim up the river’s estuary.

Scientists from the University of Nottingham, HR Wallingford and the University of Southampton worked with the Zoological Society of London (ZSL) on the research published in Ecological Modelling. It explores the theory of where the eels swim, and at what depths, which will help conservationists to identify problem areas in the Thames and secure funding for measures to help the eels migrate safely.

The European eel is a mysterious and often overlooked creature. After starting their lives at an unknown location in the Sargasso Sea, near Bermuda, the eels drift across the Atlantic and navigate up the rivers of Europe, including the Thames. They then live in the river for up to 30 years before waiting for a stormy night in autumn to begin the long journey back to their spawning grounds.

A traditional London delicacy, the creatures now face even more pressing problems than fishing threats. Since the 1980s, eel numbers have seen a decline of around 95% and have been placed on the International Union for the Conservation of Nature’s ‘Red List’. The decline in numbers is believed to be for a number of reasons, but a big problem in rivers is that eels are unable to swim past hazards and barriers, such as weirs, sluice gates, power station intake pipes, hydropower devices and dams.

By demystifying where the eels swim, and at what depths, the new study will help conservationists to identify problem areas in the Thames and secure funding for measures to help the eels migrate. The new work can also help with selecting eel-friendly sites for new developments and to design low-impact infrastructure. The method can be applied anywhere in the world that eels are in danger from human structures such as tidal turbines, power stations and factories.

Tom Benson, senior scientist at HR Wallingford explains: “To build the model we took information about the eels’ swimming habits, such as the fact that they follow freshwater and swim at different depths during the day and night, alongside information about the river, such as direction of the tide and the salinity gradient. We then checked the results against the actual numbers of eels caught in eel traps at Brentford Lock, which were set up by ZSL and monitored by citizen science.”

It was fascinating and great fun to work with the research team to turn our understanding of eel behaviours and knowledge of river flows into predictive models. Exploring various assumptions allowed us to work out which combinations of swimming behaviour were consistent with the data from ZSL.

Alison Debney, Conservation Programme Manager at ZSL said: “We’re delighted that our information will help conserve this critically endangered species and help with the good management of our river systems. Once again, our citizen scientists have helped shape cutting-edge science, in this case ensuring effective mitigation measures for eels, and helping humans and wildlife to coexist.”

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