European eel conservation

ZSL thames eel survey

Since spring 2005, ZSL has been working to conserve these iconic London inhabitants as part of our Tidal Thames Conservation Project. Most of our research is focused on the upstream elver (young eels) migration and what has driven the decline in returning elvers (known as recruitment) over the past 25-30 years. To find out about our survey methods, engagement with industry and how you can get involved please browse the web pages below..

You can also download the report on our findings from our citizen science surveys here: PDF icon 2015 ZSL elver report (970.31 KB)

Why we are there

The European eel (Anguilla anguilla) is classified as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. ZSL’s research has shown that the recruitment of the European eel has declined by up to 95% over the last 25-30 years in some tributaries of the Thames. Reasons for its decline are suggested as being a combination of habitat loss, barriers to migration, parasites, pollution, over-fishing and climate change affecting oceanic currents.

Find out more about the European eel on our eel infographic

Monitoring elver migration

ZSL is monitoring the upstream migration of the European eel in the Thames and its tributaries. Throughout the summer the ZSL team circumnavigate London on the search for eels in order to understand their unique life-cycle and the pressures on their population.

Eel movement in marshland

ZSL is working with the Environment Agency to assess resident eel populations in marshland. These are thought to be important habitats, where the eels can spend up to thirty years feeding and growing before returning to the Sargasso Sea. From June 2014, ZSL conservationists will be working on a tagging project to assess how eels use these wetlands. In addition to monitoring movement of the eels, we are also investigating local ecological and management factors, all of which will inform regional and national conservation strategies.

New monitoring technology 

ZSL and the Environment Agency are embarking on trials of innovative new technology for monitoring downstream migrations of mature European eels. Using ARIS - Adaptative Resolution Imaging Sonar, to record videos of eels, we hope to provide new insights and valuable information on the numbers of eels leaving Thames tributaries on their migration to the Sargasso Sea.

Thames Eel Management Plan 

ZSl works closely with the Environment Agency to develop and deliver the eel management plan for the Thames region. The management plan outlines key targets and measures to improve the population and conservation of the European eel.

Sustainable Eel Group

ZSL is one of the key organisations involved in the Sustainable Eel Group (SEG) which is a made up of scientists, conservationists, policymakers and commercial sectors to support the recovery of the European eel. Much of their recent work has been in relation to the European eel fishery, highlighting the importance of cross-sector collaborations to manage stocks sustainably


Citizen Science Programme

ZSL thames eel survey

Do you want to help save London's eels? The citizen science programme works with members of the public to check ZSL elver traps, located on 10 tributaries, twice a week. The volunteers don their waders to count and measure elvers before uploading the data onto the ZSL database. This is a great opportunity for members of the public to get involved in essential conservation work so if you would like to join our growing team of citizen scientists.

Find out more


Project Information

Key species:

  • European eel (Anguilla anguilla)

People Involved:

  • Joe Pecorelli, Anna Saltmarsh and Clara Obregon work on the European eel conservation project.
  • Joe Pecorelli leads the Citizen Science Eel Programme.

Partners and Sponsors:

  • Environment Agency

Kindly funded by:

  • Environment Agency
  • Esmee Fairbairn Foundation
  • D’oyly Carte Charitable Trust
  • SITA Trust
  • Panton Trust




Eel Animation

Find out about the incredible life cycle of the Critically Endangered European eel and their amazing migration.

ZSL thames eel survey

Find out about how ZSL are monitoring the Critically Endangered European eel.

Eel being measured conservation survey

Learn about how ZSL are monitoring the critically endangered European eel.

Citizen Scientists help save the European eel

In 2011, in order to expand ZSL’s eel monitoring programme we began to enlist the help of volunteers and partnership organisations. ZSL now works with fourteen partnership organisations and, to date, has trained over 350 volunteers to become eel monitoring citizen scientists. The project has become the largest and most wide-ranging study on eel migration through a single catchment in the UK. The information from the study not only allows us to refine eel pass prioritisation by highlighting barriers to upstream migration. It also provides a unique insight into the numbers of elvers entering the Thames region each year that has value at a national scale.

ZSL Citizen Scientists with eels on the River Brent in 2014
ZSL Citizen Scientists with eels on the River Brent in 2014

A new phase for the our citizen science eel project

In 2013 ZSL started to move to a new phase of the citizen science eel project. Basing our site selection on interpretation of the data collected over previous year’s eel monitoring. We have started working with our citizen science partners to make physical improvements to rivers to facilitate the upstream migration of eels. Two eel passes have been installed, one on the River Darent and the other on the Hogsmill River. On the Hogsmill, soon after the pass was installed, we were delighted to have trapped elvers for the first time just upstream of it. We plan to continue this work of opening up more freshwater habitat to eels into the future.

Come and join us

Monitoring starts in April and finishes at the end of September. We are always looking for new volunteers and new partner organisations to join this project. If you would like to help please contact:

Thank you!

We would like to thank all of our citizen scientists for their time diligently checking eel traps come rain or shine.

We'd also like to thank our project partners: Kingston University, The South East Rivers Trust, Medway Valley Countryside Partnership, North West Kent Countryside Partnership, Ham United, The Environment Trust for Richmond upon Thames, London Wildlife Trust, Friends of The River Crane Environment, Thames 21, The Wildfowl and Wetland Trust, The River Chess Association, Historic Royal Palaces, The Spelthorne Natural History Society, The Thames Anglers Conservancy and the Environment Agency.

PDF icon 2015 ZSL elver report (970.31 KB)

PDF icon 2013 citizen science eel project report (1.84 MB)

Project information

Key species:

  • European eel (Anguilla anguilla)

People Involved:

  • Joe Pecorelli is the project lead of ZSL’s Citizen Science Eel Programme

Kindly funded by:

  • Esmee Fairbairn Foundation

Project Partners:

  • Kingston University
  • The South East Rivers Trust
  • Medway Valley Countryside Partnership
  • North West Kent Countryside Partnership
  • Ham United
  • The Environment Trust for Richmond upon Thames
  • London Wildlife Trust
  • Friends of The River Crane Environment
  • Thames 21
  • The Wildfowl and Wetland Trust