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-gathering ...

that uses

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

electricity flowing between a submerged

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

and

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

. This affects the movements of nearby

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

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 catch ...

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, population density and

species composition Relative species abundance is a component of biodiversity and is a measure of how common or rare a species is relative to other species in a defined location or community.Hubbell, S. P. 2001. ''The unified neutral theory of biodiversity and biogeog ...

. 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 a gas). In electrochemical cells, electrodes are essential parts that can consist of a variety ...

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. Teams of at least two people are recommended for an effective electrofishing crew: one to operate the anode, and the other to catch the stunned fish with a dip net.

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 gasoline powered. They employ a

transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...

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 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 dip net. 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, while longer cathodes and anodes allow the crew to sample larger 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, 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 by population (United Nations), most populous country since ...

n State of

Kerala Kerala ( , ) is a States and union territories of India, 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 ...

. This can result in accidental deaths due to

electrocution Electrocution is death or severe injury caused by electric shock from electric current passing through the body. The word is derived from "electro" and "execution", but it is also used for accidental death. The term "electrocution" was coined ...

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

. 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 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. When performed incorrectly, electrofishing can injure 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 is 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 against the huntin ...

. For example, in

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

, 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 Geography of the European Union, located primarily in Europe. The u ...

banned pulse

trawling Trawling is an industrial 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 di ...

in 2006 and again in 2019; the

European Court of Justice The European Court of Justice (ECJ), officially 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 Union, it is tasked with interpreting ...

upheld the ban in 2021 after being challenged by the

Dutch Dutch or Nederlands commonly refers to: * Something of, from, or related to the Netherlands ** Dutch people as an ethnic group () ** Dutch nationality law, history and regulations of Dutch citizenship () ** Dutch language () * In specific terms, i ...

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)
{{Authority control Fishing techniques and methods