Often salmon and trout are given greater amounts of attention than our other native fish species, in part due to their popularity amongst anglers and because they are under increasing pressures from a variety of sources. However today we finished the installation of a dedicated ‘eel pass’. Over the course of the last week or two we have installed eel brushes on the Garden Weir on the Lugton Water (tributary of the River Garnock). Low water levels have been necessary to allow us to do this work and we took advantage of low levels to finish this work on what has been a very fine (dare I say spring!?) day.
Getting the levels right to ensure a flow of water over the brushes even in low summer levels. A rebate was cut to precise depth to allow the surface of the brushes to remain wet at all but the lowest summer flows. It was essential not to go too deep as there was a risk that the flow through the fish pass could be compromised.
Essentially eel brushes are stiff bristle brushes, akin to a byre brush mounted in a flexible rubber compound. The bristles act as a climbing substrate for migrating elvers and allow these small fish grip, which the weir lacks as they make their way upstream. The cry from some anglers will always be “I’ve caught eels upstream, so they must get over”. And there is no disputing that eels can get over the weir unaided. However as with any fish species at an obstacle some may get over but many others won’t. Others may just take longer to progress over the obstacle making them more susceptible to predators and increasing the energy expenditure of the migration.
Evidence that poaching is still an issue on the Lugton Water. The trough midway up the weir presents an issue as salmon make it into the trench and are vulnerable to poachers. This home-made gaffe was obviously in use last year judging by the amount of rust on the shaft. We found this in the river just downstream of the the weir.
Garden Weir now has a salmon/trout pass to help improve fish passage so why should eels be afforded any less help? With numbers in decline, these highly protected fish need all the help they can get.
Garden Weir fish pass, looking downstream through the pass.
We mounted the bristle brushes to a HDPE plastic backboard anchored onto the face of the weir in a recessed channel. The recess will help maintain a flow of water through the brushes in even low levels. See the images below for a rough step by step in the process. We’ll now have to wait until early summer to see if the elvers will use our brushes. I look forward to reporting a good news story in a few months time.
The first job was to cut the recess for the brushes to sit in. A mix of dust and water made this a filthy job. All our power tools operate at 110 volts for safety.
This picture neatly shows the bristles mounted to a sheet of HDPE plastic with stainless steel threaded bars that sit into holes drilled into the weir. These holes are filled with a resin that will hold the tile arrangement for years and years to come.
An eels eye view of the bristles. The brushes sit down into the trough of the weir and should make for an easy ascent over the vertical face. These brushes have two different bristle spacings to allow larger eels and elvers to use them.
The finished article. A neat, inconspicuous strip on the weir face.
Thanks to our partners in this project, North Ayrshire Council and SEPA.
