Eel escapement: Why restoring the population is a must

Sustainability April 14, 2020

By Dr Peter Walker, Associate Director and Aquatic Ecology Lead

The eel, recognised for its snake-like appearance, is a mysterious creature that we know relatively little about. Despite rapidly declining numbers, resulting in a critically endangered conservation status, there are relatively few current studies to try and rectify this lack of knowledge. In recent decades, the global European eel population has undergone a catastrophic decline; numbers are now estimated at just 5% of what they were in the 1970s. With eels previously representing >50% of standing fish biomass in most European aquatic environments (May & Marshall, 2008), they form a critical part of our balanced ecosystem, acting as prey for many species including otter, bittern and osprey. In order to protect this elusive creature, we must commit to finding out more about it, particularly its preferred habitat.

RSK is currently working on a habitat assessment project for the UK Environment Agency. The project aims to find a way to improve the habitat for, and subsequently population size of eel in UK waterways. This comprises a desk-based study, development of a habitat assessment tool, field trials and informed decision making for actions from the Environment Agency. As more is learnt about the habitat preferences of the eel, measures can be taken to ensure that the UK’s waterways are adequately adapted to meet these needs.

Adult silver eel ready to migrate out to sea

One must is that eels need a suitable level of connectivity between the sea and rivers and within the length of rivers to help them access important habitat and to escape back to the sea as they leave inland waters to cross the Atlantic to spawn in the Sargasso Sea. Eel passes can be installed to aid upstream migration and water abstraction pumps, needed for flood control, can be made fish friendly or screened to ensure they don’t prevent them from making their seaward journey.

However, there is a substantial cost associated with these measures. Fish-friendly pumps cost up to several hundred thousand pounds, so it’s not something that can be done without being sure they are making a difference. Research into the eel’s preferred habitat can help verify if pumps or passes will be effective and, in some cases, identify alternative, more cost-effective habitat protection or improvement methods. If, for example, a habitat is identified as unsuitable for eels, spending hundreds of thousands on specialist pumps is unlikely to improve escapement numbers. If appropriate, steps can be taken to make the habitat preferable to the eel first, and then the relevant pumps can be installed. In other cases, the habitat will never be attractive to eels, in which case our time and expenses can be better used elsewhere.

Pete releasing an eel after measuring

Anyone abstracting water from UK rivers and canals, including water companies, power stations, agriculture practitioners, industrial operators and hydro-power companies, may be subject to eel screening under The Eels (England and Wales) Regulations 2009. Should a significant number of the species be discovered, the relevant bodies may be required to install eel passes through physical obstructions or mesh screens on water intakes and discharges. This aims to improve the escapement of silver eels.

The 2009 regulations represent a step in the right direction in recognising the seriousness of the eel’s decline. However, there is much more that could be done to understand the species, its habitat and how we can best protect it. Through increased research we can find a path to restoring eel numbers to their former glory and to re-establishing the balance of our ecosystem, to the benefit of us all.

Dr Peter Walker is an Associate Director and the aquatic ecology lead within RSK Biocensus, part of RSK Environment Ltd and the wider RSK Group.

If you would like to know more about eels, including ways to help protect them or enhance habitat for the species you can contact Peter at


Surveying eel habitat