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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.[1]
Method
Electrofishing relies on two electrodes which deliver direct current at high-voltage from the anode to the cathode through the water.[2] When a fish encounters a large enough potential gradient on this path, it becomes affected by the electricity. Usually pulsed direct current (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
Electrofishing by boat
There are three types of electrofishers: backpack models, tote barge models, and boat mounted models, sometimes called a stunboat.[2]
Backpack electrofisher generators are either battery or gasoline 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, twometer 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.[2] The stunned fish swim toward the anode, where they are caught alive using a dip net.[3] 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 Indian State of Kerala. This can result in accidental deaths due to electrocution.[4]
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 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,[5] this is more common and severe in longer fish.[6]
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.[7]
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. For example, in Florida, as in many other states, it is illegal for recreational use.[7]
Electrofishing is potentially dangerous, or even lethal.[9] 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,[10] 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.[2][7][11]
↑ 2003 study: Immobilization Thresholds of Electrofishing Relative to Fish Size, biologists Chad Dolan and Steve Miranda
↑ Steven R. Dalbey; Thomas E. McMahon; Wade Fredenberg (1 August 1996). "Effect of Electrofishing Pulse Shape and Electrofishing-Induced Spinal Injury on Long-Term Growth and Survival of Wild Rainbow Trout". North American Journal of Fisheries Management. 16 (3): 560–569. doi:10.1577/1548-8675(1996)016<0560:eoepsa>2.3.co;2. S2CID35356334.
Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically conducting phase between electrodes separated by an ionically conducting and electronically insulating electrolyte.
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel and an oxidizing agent into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requiring a continuous source of fuel and oxygen to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from substances that are already present in the battery. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.
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A vacuum tube, electron tube, valve, or tube is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
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Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it can move away by an electric current or electrical discharge. The word "static" is used to differentiate it from current electricity, where an electric charge flows through an electrical conductor.
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A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, producing a phenomenon known as a Townsend discharge. Gases used include mercury vapor, xenon, neon, and hydrogen. Unlike a vacuum tube (valve), a thyratron cannot be used to amplify signals linearly.
Asian carp is an informal grouping of several species of cyprinid freshwater fishes native to Eurasia, commonly referring to the four East Asian species silver carp, bighead carp, grass carp and black carp, which were introduced to North America during the 1970s and now regarded as invasive in the United States. These four species, now also known commercially as Copi in the United States, are staple food fish in their native China, where they are collectively known as qing cao lian yong (青草鲢鳙) or si da jia yu and are farmed extensively.
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Douglas Dam is a hydroelectric dam on the French Broad River in Sevier County, Tennessee, in the southeastern United States. The dam is operated by the Tennessee Valley Authority (TVA), which built the dam in record time in the early 1940s to meet emergency energy demands at the height of World War II. Douglas Dam is a straight reinforced concrete gravity-type dam 1705 feet long and 202 feet high, impounding the 28,420-acre (11,500 ha) Douglas Lake. The dam was named for Douglas Bluff, a cliff overlooking the dam site prior to construction.
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Electric pulse fishing is a fishing technique sometimes used in trawl fisheries which produces a limited electric field above the seabed to catch fish. The pulse trawl gear consists of a number of electrodes, attached to the gear in the tow direction, that emit short electric pulses. The electrodes replace the tickler chains that are used in traditional beam trawl fishery. The pulse trawl fishery is mainly aimed at flatfish like sole, with by-catch plaice. In addition, the pulse trawl gear is applied in shrimp fisheries on a limited scale. Technically, the use of electricity to catch fish is prohibited in European waters. However, the European Union is able to provide exemptions to this rule since 2007. These exemptions are now mainly used by Dutch and British trawlers in the North Sea.
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Electric fishing can refer to one of two methods of fishing:
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