‘Eely’ Good Fun: Monitoring Eels with the Environment Agency

Earlier this week, the Essex & Suffolk Rivers Trust team met up with Fisheries Scientist Ben Norrington from the Environment Agency to learn more about eel monitoring on the River Stour.

Our visit took us to Judas Gap Weir at Flatford, a broad-crested concrete weir measuring around 20.98 metres wide. The weir marks the tidal limit of the south channel of the River Stour and includes a fish pass, helping fish to navigate their way upstream.

• 

  A sign for Judas Gap Weir on the River Stour

• 

  Judas Gap Weir

• 

  The other side of Judas Gap Weir

Photos of the river Stour and Judas Gap Weir at Flatford, Suffolk

Helping eels on their journey

European eels (Anguilla anguilla) have experienced a severe decline in numbers across England and Europe. To help address this, eel passes have been installed at more than 500 Environment Agency river structures, including dams, weirs and tide gates.

These passes are designed to make it easier for juvenile eels, known as elvers, to migrate upstream. Unlike many fish, young eels are capable of wriggling and climbing their way over damp surfaces, allowing them to navigate structures that would otherwise be difficult or impossible to pass.

But how do you know whether an eel pass is working? That is where monitoring comes in.

• 

  ESRT staff collect water quality measurements

• 

  Eel pass water tank at the top of the weir

• 

  A juvenile eel

1. Collecting water quality measurements. 2. The tank of the eel pass at the top of the weir. 3. A juvenile eel

Think like a fish!

During our visit, Ben showed us how the Environment Agency monitors eel movements and assesses the effectiveness of eel passes.

One of the key messages was to ‘think like a fish’. When looking at a river structure, it is important to consider the journey from the perspective of the fish: Where would it naturally want to go? What might be stopping it? Where would it look for a way around a barrier?

It was a fascinating reminder that even relatively small changes to the way a river is connected can make a big difference to fish and eel migration.

How do you measure an eel?

Of course, no eel monitoring session would be complete without getting up close to some eels!

• 

  The ESRT team have a go at measuring slippery eels!

• 

  An eel is measured

• 

  The ESRT team have a go at measuring slippery eels!

The ESRT team have a go at measuring slippery eels!

The team had the opportunity to learn how eels are handled and measured as part of the monitoring process. Length is one of the key measurements recorded, alongside water quality and climate data that can help scientists understand eel populations and their movements.

And naturally, we couldn't resist giving our slippery subjects some suitably ‘eely’ names – including Eel-vis Presley, Shaqu-eel O’Neal and Eel-izabeth Taylor!

While the puns may have been questionable, the monitoring itself is an important part of understanding how eels are using our rivers and whether measures such as eel passes are helping them on their journey.

Removing barriers to fish migration

Improving fish passage is an important part of restoring healthy, connected rivers. Across Essex, work is being supported by the Essex Fish Migration Roadmap, which identifies opportunities to improve connectivity and remove or modify barriers that prevent fish from moving freely through our river systems.

At ESRT, helping to remove barriers to fish migration is a key part of our work. We know that restoring natural connectivity cannot be achieved by one organisation alone, which is why partnership working is so important.

By working alongside organisations such as the Environment Agency, water companies, landowners and local communities, we can identify opportunities to make our rivers more accessible for fish and other wildlife.

So, while our visit to Judas Gap involved plenty of eels, measuring and a few terrible puns, it was also a valuable opportunity to learn more about the challenges faced by migratory fish and the practical steps we can take to help them.

After all, when it comes to river restoration, sometimes it pays to think like a fish!

Find out more:

• Explore the Essex Fish Migration Road Map

• Read our blog post on Fish Surveys, Elvers and Partnership Working