Over the years The Welsh Dee Trust has undertaken a range of projects to improve the aquatic and riparian environment. The projects have ranged from instream habitat improvements, riparian zone improvements, gravel trap creation to assist spawning, clean and dirty water separation, fencing to reduce diffuse rural pollution and weir removal to list a few.
Having completed a project, we believe we have made an improvement to the water quality and/or aquatic environment, but the only way of really knowing if there is a benefit is to undertake some monitoring. One of the techniques the Trust use is Electricfishing. The Electricfishing surveys are generally carried out over a 50m stretch of river.
Before undertaking any electrofishing surveys we must apply to Natural Resources Wales (NRW) for a consent.
For those not familiar with the technique, in simple terms, electrofishing uses direct current electricity flowing between a cathode and an anode in the river. This affects the movement of the fish so that they swim toward the anode, where the fish are netted. When performed correctly, electrofishing results in no permanent harm to fish, which return to their natural state almost immediately.
The species of fish are identified, measured and kept out of the river until the end of the survey when they are returned unharmed.
The main reason for the monitoring is to look at salmonid juvenile recruitment -Salmon, Sea Trout and Brown Trout. There’s another benefit of using this technique in that we also catch other species of fish. The River Alyn used to have a large abundance of minnows, but they mysteriously disappeared several years ago. Two years ago, we picked up a few minnows in our electrofishing sample and have now noticed an increase in numbers within the river. Again, this year we picked up a juvenile Roach in the Alyn, this wouldn’t have been found without using this monitoring technique. Similarly, a Brook Lamprey was found in our electrofishing sample.
Below are the results from 2 differing rivers. The Abbey Brook, near Llangollen and the River Alyn, near Rossett. Abbey Brook has no real urban pressure on it. The only pressure is from agriculture (primarily sheep farming) were as the River Alyn has a lot more pressures from river modification, industry, water treatment works, recreation and agriculture.
The Abbey Brook Near Llangollen
The River Alyn Rossett