European eel conservation

ZSL thames eel survey

With the vital help of citizen scientists and partner organisations ZSL has been working for the survival of Critically Endangered European eels.

Volunteer as a citizen scientist

Why are we monitoring eels?

European eels (Anguilla anguilla) were once thriving London’s rivers but have seen up to a 95% decline over 25-35 years and the species now is classified as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. We need your help monitoring the upstream elver (young eels) migration through the Thames from the Atlantic’s Sargasso sea in order to support this migration, better understand their plight and work to provide a solution to their decline.

Over a decade of data gathering suggests that declines are down to combination of habitat loss, barriers to migration, parasites, pollution, overfishing and climate change affecting oceanic currents.

How can you help?

By volunteering as a citizen scientist to help us count, weigh and measure eels arriving in eel friendly traps laid out across London’s rivers you can enable ZSL to maintain and massively scale up vital work aimed at understanding their unique life-cycle, the pressures on their population and informing the management plan for their survival.

Volunteer data on eels is taken during their local migration months between April to September each year and gives us a much better view of what is happening across the Thames catchment in London’s rivers.

Volunteer as a citizen scientist

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

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:

  • The City Bridge Trust
  • Environment Agency
  • D’oyly Carte Charitable 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.