Victoria Franklin – Conservation Trainee
Last week some National Park Volunteers (all fully trained) have finally been able to carry out the first electro fishing surveys this year along the River Esk. Delays had been caused by the weather.
The priority are sites up and downstream of the Sewage Treatment Works (STW) and one Combined Sewer Overflow (CSO) in the upper catchment. The first day of surveying was at Commondale.
The concept of electro fishing is to collect samples of fish living within the river, the higher the fish count the healthier the river should be. This will also show the type of fish living in our rivers, the cleanliness of the river and theoretically what the invertebrate population is like along that stretch of river.
The river levels had settled down by Thursday meaning the water was back to a slow flow and all the previous rain had made the water clear giving the perfect conditions for electro fishing.
We fished the river in two 50m sections, one upstream and one downstream of water treatment works. This was done using a zig zag motion to ensure that no area was left unfished. Each 50m section was fished three times to ensure a fair population of fish were caught.
The equipment used to stun the fish is called an electro fisher and consists of a positive charge the anode at the front and a negative charge called the cathode which trails along the back. These are both attached to a battery which is worn by the person conducting the fishing, today it was Volunteer Paul. Both the anode and the cathode must be in the water to cause an electro charge which is what stuns the fish, but don’t worry rubber thigh waders were worn by everyone so the electro pulse did not affect us humans like it did the fish. The rest of us were in charge of catching the stunned fish in nets alongside the anode, which is harder than it looks as the fish soon spring back to life! They are then transferred into a bucket from the nets.
We set the voltage output at 150- 200 volts which is enough to temporarily stun the fish making them easier to catch in the net. Once the section of river has been fished the data collection begins. The fish are identified – on this day we found 57 trout downstream and 104 upstream with the largest being 180mm and the smallest recorded at 52mm. The information collected will now be analysed before being sent onto Yorkshire Water, they will then compare this with the other locations which are due to be fished over the next few weeks, and that will all help inform management of their sites as necessary.
An amazing day was had by all the volunteers and staff that attended. More data collection will happen in the next few weeks on different sites along the Esk.