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 juveniles (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..

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.

Conserving the European Eel

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.

Citizen Science Programme

Want to help save London's eels? The citizen science programme relies on members of the public checking ZSL elver traps, located on 7 tributaries of the Thames, twice a week. The volunteers don their waders to count and measure elvers before uploading the data onto the ZSL database. It is a great opportunity for members of the public to get involved in essential conservation work and if you would like to join our growing team of citizen scientists, please do get in touch.   

Monitoring and tagging eels

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 October 2013, 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.

Technology for monitoring eel migration

ZSL and the Environment Agency are embarking on trials of innovative new technology for monitoring downstream migrations of mature European eels. Using DIDSON - Dual Frequency Identification Sonar – technology to capture eels on 'film', it is hoped that this new method will help in monitoring the numbers of eels leaving Thames tributaries to begin their migration to the Sargasso Sea.

London Eel Action Plan 

London's rivers face multiple pressures from the growing populations that surround them. The London Eel Action Plan (LEAP), under the guidance of the Environment Agency's Thames catchment fisheries team, uses the European eel as a flagship species to improve rivers for eels and consequently other fish and wildlife.

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. 

Project information

Key Species

European Eel (Anguilla anguilla)

European eels have a long and complex life cycle. They are a migratory, catadromous fish, feeding and growing in fresh water but returning to the sea to spawn.

People involved

Steve Mowat is the project manager for ZSL’s Thames Eel Projects

Joe Pecorelli runs the Citizen Science programme.

Matthew Gollock chairs the IUCN Anguillid Specialist Sub-Group.

Partners & Sponsors

  • Environment agency
  • Esmee Fairbairn Foundation
  • Doyly Carte Foundation