A SURVEY using an electric current to temporarily stun fish has revealed the wide variety of aquatic life in the River Stour.

Hundreds of fish across a wide variety of species were found during the survey near Dedham.

They included eel, flounder, chub, tench, pike, bullhead, perch and gudgeon.

The Environment Agency carries out fish surveys along all the main rivers and tributaries in East Anglia.

It can take 10 to 12 hours on a busy day.

Dan Hayter, a fisheries specialist who has worked for the Environment Agency for 20 years, explained the process.

He said: “To conduct a fish survey, we measure out a 100-metre stretch of the river and place a large stop net at the start and end of the stretch to prevent fish moving in and out during the survey.

“Four of us then get in a motorised boat and travel along the stretch with specialised electric fishing equipment.

“We usually have one person manoeuvring the boat, two people operating the handheld electrodes – stainless steel hoops on the end of a long pole – and one with a net catching the fish, moving them to a recovery and holding container ready for us to count.

“Electric fishing involves us passing a mild electrical field through the water to temporarily immobilise the fish. This allows us to catch them.

“Electro fishing may sound a little scary, but it is harmless to the fish and is a very humane way of catching them and allowing us to carry out this vital work.

“When conducting the survey, we start in the middle of the stretch first and then go along the sides, using the current to safely capture the fish.

“We then repeat this once or twice more to ensure we have a good capture efficiency and get accurate fish data.”

The surveys are done for several reasons, including for information about fish stocks and to discuss the health of the river.

Mr Hayter said: “When we count the fish, we note down the species and length.

“During our survey along the river Stour we caught 15 species and more than 600 fish including eel, chub, roach, bleak, dace, tench, pike, bullhead, spined loach, gudgeon, perch and flounder.

“At the end of the survey all of the fish get returned to the river and the nets are removed.

“We have 40 years of data for this stretch of river making it one of the best data sets for electric fishing in the UK.”