Electrofishing

before they are caught. 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 fish, which return to their natural state in as little as 2 minutes after being stunned.

There are three types of electrofishers: backpack models, towed barge models, and boat mounted models, sometimes called a stunboat. All models rely on two electrodes which deliver current into the water to stun fish. The current runs from the anode to the cathode, creating a high-voltage potential. When a fish encounters a large enough potential gradient, it becomes affected by the electricity. Usually pulsed DC current is applied, which causes galvanotaxis in the fish. Galvanotaxis is uncontrolled muscular convulsion that results in the fish swimming toward 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.

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, 2 meter pole and is usually in the form of a ring. The cathode is a long, 3 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 incapacitates 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.

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.

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. [cite web
url=http://www.petitcodiac.com/eFishing/electroFishing.htm
title=Electro-Fishing Summary
year=2003
month=September
accessdate=2007-08-09]

----A relatively new fishing technique is electrofishing (electric fishing). Electrofishing is used primarily in freshwater by zoologists as a sampling technique. Typical uses include collecting fish for stream classification surveys such as Index of Biotic Integrity surveys, to capture brood stock for hatcheries, or to collect representative samples from fish populations for the estimation of population size and structure. Most commonly, pulses of direct current (DC) are used to induce capture-prone behavior in fish. For example, with the apparatus correctly tuned as to pulse speed, voltage gradient and current, fish will exhibit galvanotaxis; they turn into the electric field and swim toward the apparatus.

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, which is determined by the concentration in the water of charge carriers (ions), influences the shape and extent of the electric field in the water and thus affects the field's ability to induce capture-prone behavior in the fish.

Electrofishing systems can be powered by one or more batteries or by a generator and come in various sizes, from those that are mounted to a backpack to those mounted in large boats. Systems are typically equipped with various safety devices including one or more dead man's switches and a tilt switch designed to disable the device if the unit is tipped beyond a certain limit by, for example, the operator becoming incapacitated or falling into the water. Rubber gloves and rubber boots must be worn to isolate the operator and to prevent electrocution.

Notes

References

* Helfman, Gene S (2007) [http://books.google.com/books?id=eGGqGYEQXDkC&pg=PA453&dq=Electrofishing+date:2000-2008&lr=&num=100&as_brr=0&ei=aQXkSPjIFZPqMv_lrfYP&sig=ACfU3U3rDS4k0YaWIUkzIe5lVnb0rw8GeA "Fish Conservation: A Guide to Understanding and Restoring Global Aquatic Biodiversity and Fishery Resources"] Island Press, pp. 452–453. ISBN 9781559635967
* Hill, David; Fasham, Matthew; Tucker, Graham; Shewry, Michael and Shaw, Philip (2005) [http://books.google.com/books?id=5tmHpmKOmKsC&pg=PA384&dq=Electrofishing+date:2000-2008&lr=&num=100&as_brr=0&ei=aQXkSPjIFZPqMv_lrfYP&sig=ACfU3U19fzbK2z1bNdTztwiiY6WpzfheaQ#PPA384,M1 "Handbook of Biodiversity Methods: Survey, Evaluation and Monitoring"] Cambridge University Press, pp. 383–385. ISBN 9780521823685
* [http://www.nps.gov/wica/naturescience/fishery-research-electrofishing-procedure.htm "Fishery Research - Electrofishing"] National Park Service, US Department of the Interior. Retrieved 2 October 2008.
* U.S. Fish and Wildlife Service (2004) [http://www.fws.gov/policy/241fw6.html "Electrofishing"]

External links

* [http://www.fw.delaware.gov/Fisheries/Documents/electrofish.pdf Delaware Division of Fish and Wildlife, Fish Monitoring via Electrofishing]
* [http://www4.ncsu.edu/~tkwak/injury.html Electrofishing Effects on Endangered Fishes]
* [https://www.fws.gov/lists/listinfo/electrofishing International electrofishing email forum]
* [http://www.salishsea.ca/resources/Inventory/Fish%20Capture/electrofishing.htm Electrofishing]