Electrofishing is a

fishing technique Fishing techniques are methods for catching fish. The term may also be applied to methods for catching other aquatic animals such as molluscs (shellfish, squid, octopus) and edible marine invertebrates. Fishing techniques include hand-gatherin ...

that uses

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or ev ...

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...

flowing between a submerged

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

and

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

. This affects the movements of nearby

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

so that they swim toward the anode, where they can be

caught Caught is a method of dismissing a batsman in cricket. A batsman is out caught if the batsman hits the ball, from a legitimate delivery, with the bat, and the ball is caught by the bowler or a fielder before it hits the ground. If the ball h ...

or stunned."FISHNET SHOCKINGS"
. ''Toronto Star'', December 3, page IN3. Paul Hunter Electrofishing is a common scientific survey method used to sample fish populations to determine abundance, density and species composition. When performed correctly, electrofishing results in no permanent harm to the fish, which return to their natural mobility state in as little as two minutes after being caught.

Method

Electrofishing relies on two

electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials dep ...

which deliver direct current at high-voltage from the anode to the cathode through the water. When a fish encounters a large enough potential gradient on this path, it becomes affected by the electricity. Usually pulsed

(DC) is applied, which causes galvanotaxis in the fish. Galvanotaxis is uncontrolled muscular convulsion that results in the fish swimming towards the anode. At least two people are required for an effective electrofishing crew: one to operate the anode, and the other to catch the stunned fish with a

dip net A hand net, also called a scoop net, is a fishing net or meshed basket held open on a rigid hoop, which may or may not be mounted to the end of a handle. A hand net with a long handle is often called a dip net. When it is used by an angler to ...

Types

There are three types of electrofishers: backpack models, tote barge models, and boat mounted models, sometimes called a stunboat. Backpack electrofisher generators are either battery or gas powered. They employ a transformer to pulse the current before it is delivered into the water. The anode is located at the end of a long, two meter pole and is usually in the form of a ring. The cathode is a long, three-meter braided steel cable that trails behind the operator. The electrofisher is operated by a

deadman's switch A dead man's switch (see alternative names) is a switch that is designed to be activated or deactivated if the human operator becomes incapacitated, such as through death, loss of consciousness, or being bodily removed from control. Originally a ...

on the anode pole. There are a number of safety features built into newer backpack models, such as audible speakers that sound when the unit is operating, tilt-switches that incapacitate the electrofisher if the backpack is tilted more than 45 degrees, and quick-release straps to enable the user to quickly remove the electrofisher in the event of some emergency. When boat electrofishing, the boat itself is the cathode, and the anode(s) are generally mounted off the bow. The stunned fish swim toward the anode, where they are caught alive using a

. Towed barge electrofishers operate similarly to backpack electrofishers, with the exception that the generator is located on a floating barge instead of on a backpack. Often the barge can be left stationary on the shore and longer cathodes and anodes allow the crew to sample large areas. Barge electrofishers often employ gas-powered generators since a user does not have to carry the extra weight on his or her back. A method of electrofishing using illegally diverted electricity from overhead electric lines is prevalent in parts of the

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...

n State of

Kerala Kerala ( ; ) is a state on the Malabar Coast of India. It was formed on 1 November 1956, following the passage of the States Reorganisation Act, by combining Malayalam-speaking regions of the erstwhile regions of Cochin, Malabar, South Ca ...

. This can result in accidental deaths due to electrocution.

Effectiveness

The effectiveness of electrofishing is influenced by a variety of biological, technical, logistical, and environmental factors. The catch is often selectively biased as to fish size and species composition. When using pulsed DC for fishing, the pulse rate and the intensity of the electric field strongly influence the size and nature of the catch. The

conductivity Conductivity may refer to: *Electrical conductivity, a measure of a material's ability to conduct an electric current **Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution ** Ionic conductivity (solid state), ele ...

of the water influences the shape and extent of the electric field and thus affects the field's ability to induce capture-prone behavior in the fish. It can also cause injury to the fish. The electricity causes muscle spasms that damage the vertebrae. For unknown reasons, this is more common and severe in longer fish. Due to the conductivity of saltwater, electrofishing is not an effective tool for catching saltwater fish, as the electricity travels through the water, rather than through the fish.

Legality

While electrofishing is used by multiple government agencies, it may be illegal to use it as a form of recreational fishing. This method can be considered

poaching Poaching has been defined as the illegal hunting or capturing of wild animals, usually associated with land use rights. Poaching was once performed by impoverished peasants for subsistence purposes and to supplement meager diets. It was set a ...

. For example, in

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...

, as in many other states, it is illegal for recreational use. The

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...

banned pulse

trawling Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different spec ...

in 2006 and again in 2019; the

European Court of Justice The European Court of Justice (ECJ, french: Cour de Justice européenne), formally just the Court of Justice, is the supreme court of the European Union in matters of European Union law. As a part of the Court of Justice of the European U ...

upheld the ban in 2021 after being challenged by the

Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () Dutch may also refer to: Places * Dutch, West Virginia, a community in the United States * Pennsylvania Dutch Country People E ...

government.

Safety

Electrofishing is potentially dangerous, or even lethal. The high voltages and currents used, compounded with the presence of water, present serious safety risks. The typical dangers of electrocution, such as electrically-induced unconsciousness and the paralysis of the heart and lungs, are compounded by the risk of drowning, which may result from the aforementioned hazards. In light of this, many safety precautions are taken for those handling electrofishing equipment and those nearby.

Notes

External links

electrofishing.net Serving the Global Fisheries Community with Training , Tools , Research

Delaware Division of Fish and Wildlife, Fish Monitoring via Electrofishing

International electrofishing email forum

What-If xkcd (Electrofishing for Whales)Efish Solutions (Equipment to assist with electrofishing, survey work and fisheries management
{{fisheries and fishing Fishing techniques and methods