European eel conservation

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

ZSL’s work for the European eel in the Thames

European eels (Anguilla anguilla) once thrived in London’s rivers but the number of young joining the adult populations has dropped dramatically since the 1980s and the species is now classified as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. ZSL’s work on European eels started in 2005 and now ranges from informing international conservation policy and leading UK research on eel behaviour to regional-scale best practice conservation delivery in the Thames Catchment. Here, through research, river improvements, public engagement and advising policy, we work in partnership with the Environment Agency and a network of other organisations to address the key conservation issues facing eels.

Reconnecting broken migratory pathways

A principal conservation action for eels in freshwater is to restore migratory pathways by removing barriers such as weirs. If removal is not possible, the impact of barriers can be partially mitigated by installing eel passes that allow eels to move upstream over them. With over 2000 barriers to migration, the Thames rivers are highly fragmented. One of ZSL’s key goals in the region is to reconnect migration routes. So far, eel passes commissioned by ZSL have made 138.95 hectares of additional habitat accessible.

Assessment of Adult European Eel Stocks in the Thames River Basin

ZSL has monitored the recruitment of juvenile eels into the Thames River Basin since 2005. The data collected to date supports the findings that the annual recruitment of the European eel across its range has reduced by 90-95% since the 1980s. It is likely that this reduction in recruitment will have had an impact on the numbers of adult eel in the Thames River Basin. In 2019, ZSL repeated surveys of adult eels undertaken in 1987 and 2011 to assess the geographic spread of eel populations in the Thames and identify the effect of the range of measures that have been introduced to improve eel stocks.

Thames Eel Management Plan 

ZSL is a key partner in delivering the Environment Agency’s Thames Eel Management Plan. The management plan outlines key targets and measures to improve the population and conservation of the European eel. Given the scale of the challenges faced by eels, working together is essential. – if you or your organisation would like to join us in this work please get in touch.

ObstacEELS

ZSL are working with partners in the Thames Rivers Trust Thames Catchment Community Eels Project to co-develop a standardised methodology for citizen science river walkover surveys with the aim of mapping barriers and assessing their impact on upstream eel migration. The barrier assessment method will be based on the EBAT scoring system and data captured using the River Obstacles App, which ZSL worked in partnership to help relaunch in 2021. This is an exciting development which will help fill data gaps on where barriers are in our rivers nationally and help river Catchment Partnerships make decisions about how to prioritise conservation action for eel and other fish species by restoring source to sea habitat connectivity.

The importance of marshes to European eels

The brackish and freshwater marshes of North Kent, that abut the sea walls of the Rivers Medway and Swale in the Thames Estuary, are important habitat for eels to grow and mature in. However, these habitats are often highly managed environments, using structures such as tidal flaps to regulate freshwater flow out of the marshes and prevent sea water flowing into them. This can impede access to these important habitats for eels.

In 2022, ZSL together with the Environment Agency, local partners in Faversham, the Medway Swale and Estuary Partnership, Kent Wildlife Trust, RSPB and citizen scientists, trialled the use of habitat collectors (commonly referred to as ‘mopheads’) at three tidal flap sites in the North Kent Marshes to try and understand how passable the structures were to eels and to inform conservation action to improve connectivity.