Electro-fishing the Worth

Earlier this month River Worth Friends and the Aire Rivers Trust electro-fished parts of the River Worth to survey the fish populations in the river. We were surveying to try to get an idea of where fish are distributed and how the many weirs affect the population. Once we have a better understanding of this we would like to remove or adjust some weirs to enable easier fish migration.
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​The survey was led by Professor Jon Grey of the Wild Trout Trust and Lancaster University who has much experience with electro-fishing and assessing fish populations.
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​Electro-fishing involves passing an electric current through the water which momentarily stuns the fish, making it possible to net them. You have to be quick with the net as they recover quite quickly. We surveyed five stretches, each about 50 metres long, and passed through those stretches  three times so theoretically we should get fewer fish with each pass. The procedure is that Jon uses a battery pack and electrode rod to create the current, sweeping from side to side across the river. Two assistants then catch any fish that emerge and place them in a bucket carried by a third assistant. After three passes the fish are counted and measured before being released back into the river unharmed. One of the tricks with this is to not put your hands in the water whilst Jon has his finger on the button!
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Jon with electrode, two nets men and a bucket carrier!

Recording fish species and length.

Working tricky currents at Malcolm's weir.

Measuring the length and width of the surveyed stretch.

Measuring a brown trout.

​We found six different species of fish during the survey, our main interest was in the two larger species we know are present from anglers reports, brown trout and grayling. We did find brown trout but not a single grayling, which is a bit of a mystery. The other species were bullhead, stone loach, brook lamprey (see our previous blog on these interesting fish), minnow and the odd three-spined stickleback.
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​We sampled sites from close to the confluence with the Aire near Kinara Close up to Damems. The distribution of brown trout was interesting with much better numbers downstream of the lowest weir (which we call Malcolm’s weir - above the A650 overpass) and in the better habitat upstream at Damems. In between all the weirs, there were relatively few. . This pattern was also apparent for bullhead, which has similar requirements for habitat and water quality as trout. Minnow and stone loach appeared affected by the weirs; their numbers were restricted to the sites downstream. Stickleback probably came in from the mill goit at Marriners Rd.
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Bull head and stone loach.

​Prof. Grey is still analysing the results but we are hoping they will help us in planning our future work on the river. It appears that the weirs are having an impact on fish populations, hindering them from colonising from the Aire. However, the picture is complicated – it appears that there are well-established populations of resident trout and bullhead above the weirs which are more likely responsible for the fish that we caught in between the weirs  We have some funding which we would like to use to make at least one of the weirs passable for fish, this would assist fish migration for breeding purposes, for feeding, and to recolonise following pollution or heavy flood events.

Close up brown trout really are beautiful fish.

River Worth Friends have various conservation activities aimed at improving the river habitat, if you would like to get involved please contact us, we would be pleased to hear from you.
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All pictures are copyright of RWF member John Tickner.