A joint effort between the Zoological Society of London (ZSL), the Thames Anglers Conservancy (TAC) and South East Rivers Trust continued the ongoing efforts to assist elvers/eels with the final stages of their long 3500 mile migration from the Sargasso Sea up into the Hogsmill catchment. In August last year, the same partners installed an eel pass onto the most downstream obstruction in the catchment at Clattern Bridge, Kingston, which showed immediate signs of success with the first elvers ever being recorded further upstream at the ZSL eel monitoring site the following week.
Upstream of Clattern Bridge the next obstacle, the Environment Agency’s gauging weir, has already an eel pass installed for several years and so this time we turned out attention to the next weir upstream. Although a few incredibly determined eels have successfully made it past this obstacle, the weir does without doubt prove to be the end of the line for many. With its vertical face, smooth sloping concrete surface and fast flows, the elvers generally have little chance of clinging on and and making it to the calm of the river bed upstream.
The sloping weir with vertical face
In order to provide purchase and slower the flows, yesterday eel tiles were installed to the weir, guiding them in at the downstream end, helping them up and over and feeding them safely into the slack water at the bed upstream. A custom built debris deflector and bracket to mount the tiles to the wall adjacent to the vertical face were manufactured by Norm Fairey, our regular go-to handy man.
Eel tiles fixed to the concrete slope
Vertical tiles to help the eels over the weir crest
Once completed we wandered down to have a look at the eel pass on the gauging station. It appears that the brush material makes a perfect media for plants to establish in, especially our arch nemesis Himalayan balsam. Concerned that the root network would be clogging the pass we set about unbolting it from the wall.
Is it an eel pass or a hanging basket?
What we found was a densely matted root system which would have prevented even the smallest elver from getting through. Each section of the pass was removed, cleared and reattached ready for the first visitor to utilise. On the whole a very satisfying day.
No way through!
All clear and ready for the first migratory visitor
It will be interesting to see the effects that these actions will have on this years monitoring undertaken by ZSL and the keen volunteers. We will keep you posted with any news. This project was funded by Defra through the Catchment Restoration Fund.
A big thanks to David Harvey and Neil Depledge from TAC and Joe Pecorelli from ZSL.
To see updates from the Wandle, please check out the website