Research theme: Electrofishing

Electrofishing is a method used to catch fish in a quick and efficient manner. At Inland Fisheries Ireland we use electrofishing to survey rivers, canals and on occasions, the shallow margins of lakes.

As its name suggests, electrofishing is a dangerous activity, as electricity and water are a very hazardous combination. Therefore, health and safety measures are very important for operators. It is crucially important that the necessary health and safety equipment is worn and that all equipment is in good working condition. Furthermore, staff are trained so that they are aware of any possible risks. If done correctly, electrofishing should cause minimal harm to fish, making it a much less damaging or, “non-destructive” way of catching fish than other methods.

If we are interested in a particular species of fish and need to learn more, we can target certain areas when electrofishing. For example, if we need to catch lamprey we might fish the muddy or silty shallows along the river margins, where they may be burrowed. If we wish to find young salmon, we fish the shallow riffles area along straight sections of river, where the water is broken and appears to bubble or boil. If we want to find brown trout, they are most often in the deeper flowing sections called glides or in the pools. On most occasions, we simply want to learn about the whole fish population in a stretch of river, so we will time our fishing and are less target-specific in our approach. By covering a variety of habitats within the river, we should find a good mix of fish.

Electrofishing uses the physiological effect of an electric field in water to stimulate a fish’s nervous system so that it swims towards the handheld net.  In best practice, the fish is attracted to the net, rather than stunned, so as to prevent harm. The charge emitted into the water causes them to turn and swim towards the net, which enables their quick removal for storage until processing.

The timing of sampling is linked to an understanding of the life history strategies of the target species.  Sampling is typically carried out towards the end of the growing season when young fish are sufficiently large enough to be identified and strong enough to withstand the shock. Fish stock assessments are usually carried out between the 1st of July and 30th of September when stream and river flows are moderate to low and less variable than during other seasons. 

• Wadeable rivers: When a river is shallow, we wade and face upstream while fishing. Usually a team consists of one person fishing and another holding a bucket to collect the fish. We use additional teams in wider channels.
• Deep rivers: Boats are used in medium sized rivers, when wading is impractical or impossible. Here our team consists of three people on a boat, one rowing and two working the nets. We use additional teams in wider channels.
• Very deep, large rivers: In very large rivers, like the River Shannon we use higher-voltage units to fish because additional power is needed to achieve the same effect.

At Inland Fisheries Ireland, we use a number of different approaches to electrofishing. Have a look at our video.

• Targeted fishing: We target specific areas because we want to catch a certain species.
• Timed fishing: We fish for a specific period of time.
• Distance fishing: We fish to cover a certain distance.
• Pulsed fishing: We use high-voltage pulses by turning on and off the power intermittently.