Eel conservation in London’s rivers

by ZSL on

Estuaries and Wetlands Intern Charlotte Hebditch reports on the progress of this year’s European eel survey.

The conservation of the critically endangered European eel has been a primary focus of ZSL’s Estuaries and Wetlands conservation team for a number of years. Unbelievably we are now two-thirds of the way through this year’s eel survey season. This summer, I’ve been lucky to spend a large portion of my week away from the office on the rivers Lea and Roding, monitoring eels as they undergo their extensive annual migration upstream.

Elvers caught in our traps on the river Roding
Elvers caught in our traps on the river Roding

Since April we have counted a total of 5232 eels between 11 monitoring sites across the city. The recent weather, alternating between scorching hot to thunderstorms has kept us on our toes, whilst ensuring some rememberable days out surveying.  Despite this summer’s prolonged heatwave making time spent out by the river more enjoyable for me, for the eels the continuous dry spell has led to a significant drop in water levels, impeding their progress upstream and into our traps for study.  However it’s not all bad news. My highlight to date was discovering a grand total of 681 eels upon opening our trap on the river Lea one morning, proof that we are making London’s rivers more accessible to the migrating eels.  

Building upon the success of European eel conservation in the Thames and its tributaries, last month, a new monitoring site was officially opened at Hall Place on the river Cray. This new addition to the river is to be celebrated, as it allows us to monitor the number of the eels progressing on their journey upstream within a new section of river. Before 2016, a large barrier on the river Cray blocked eel passage, which undoubtedly negatively impacted their migration. Challenges such as this hinders eel life-cycle completion, consequently providing a major reason as to why the eel population has suffered.

Elvers from river Lea in a net
Bumper catch on the river Lea

Last year, this barrier was made passable to eels which makes the opening of this new monitoring site further upstream even more exciting, as we eagerly await the arrival of this year’s elvers. I am happy to say that within a few weeks of opening, the first eel to pass through the site has already been found.  Achieving a high number of eel recordings will help to positively highlight the benefits of installing passes as a key tool to aiding the conservation of the European eel in London’s rivers.

New 2018 eel pass at Hall place on the river Cray
New 2018 eel pass at Hall place on the river Cray

When the survey season draws to a close in couple of months, I look forward to discovering what our conservation efforts have achieved this year, in supporting the movement of European eels upstream to help grow their population size within our city.

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