Eel monitoring at Morden Hall Park

Eels caught in a bucket for monitoring

The eel monitoring project at Morden Hall Park has now ended. Morden Hall Park was one of 13 sites along the length of the Thames where volunteers from 22 partner organisations carried out monitoring of the upstream eel migration between 2017 and 2021.

The eel monitoring project has now ended.

ZSL London Zoo says: "We would like to extend our thanks to all those who have taken part in the eel monitoring at Morden Hall Park. The data that has been collected has served its purpose in showing that European eels migrate upstream at this site and will help to ensure that any future management works must keep this in mind, as well as at other similar sites both in the Thames catchment and beyond."

A successful Heritage Lottery Fund bid allowed Morden Hall Park to pay for an eel trap and several eel passes as well as eel monitoring training for staff and volunteers. ZSL gave training to Rangers, other staff and volunteers and monitoring of eel numbers travelling up the River Wandle through the Park took place between 2017 and 2021.

Retrieving eels from the trap
A ranger retrieving eels from an eel trap
Retrieving eels from the trap

How eel monitoring works

Members of the team check the eel trap daily, measure and release the eels, and record the results, uploading them as part of a wider project. Since the monitoring began at Morden Hall Park, the trap caught over 200 eels.

The trapping season runs from mid-April to the beginning of October, while the eels are migrating from their spawning grounds in the Sargasso Sea. The trap at Morden Hall Park is catching them as they head into our rivers and find a home to grow up in.

Measuring an eel before release
An eel being measured
Measuring an eel before release

Why monitor eel numbers?

Eels are now classified as critically endangered and we’re monitoring levels because of concerns the numbers are dropping. Numbers are already down 90% on 1980s levels.

Threats to eel numbers:

  • Barriers to migration
  • Changes in climate and currents
  • Hydropower
  • Overfishing
  • Pollution
  • Parasites
  • Loss of habitat

Find out more via the ZSL website: zslsites.org/elvers/#action