Chapter 8: Electrofishing
James B. Reynolds and A. Lawrence Kolz
Electrofishing is the use of electricity to control or capture fish and is used primarily, but not exclusively, in freshwater systems. Given the expense and effort of sampling fish, the method is often effective. However, electroshock may be harmful to fish and humans, and precautions for human safety and fish welfare must be observed to minimize these risks. The basic idea of electrofishing is simple—an energy source (e.g., generator or battery) is used to electrify metal electrodes in water, creating an electrical field that stuns fish or alters their movements, thus achieving control or capture. Electrofishing may be mobile or stationary. Mobile methods involve fish capture from a boat or while wading. Stationary uses are usually aimed at diverting or blocking fish movement. Exceptions are benthic, stationary electrodes to capture fish in a prescribed area and low-energy electrodes worn to repel sharks while swimming or diving. Herein, our definition of electrofishing is broad but emphasizes capture.
Serious development of electrofishing as a scientific sampling technique began after World War II (Reynolds 1995). Research in the 1950s and 1960s was aimed primarily at development of field equipment for capturing fish and understanding fish responses in controlled electric fields. In the 1970s and 1980s, attention was given to the improvement of capture and control techniques and to the effects of electroshock on fish physiology and stress. By the 1990s, focus had shifted to sampling refinements and fish injury and mortality caused by electroshock.
This chapter is a primer on electrofishing with emphasis on its uses in North America. It provides summaries of the general principles of electricity in circuits and electric fields in water (section 8.2), effects of electroshock on fish and methods for reducing harmful effects (section 8.3), descriptions of electrofishing systems and their safe use (section 8.4), and guidelines for efficient sampling in lakes and streams, including recommendations for sampling standardization (section 8.5). A final section (section 8.6) addresses the role and ethical use of electrofishing in fisheries science. References are provided for detailed direction in given situations (e.g., Burkhardt and Gutreuter 1995, standardization; Meador et al. 2003, single-pass sampling; Miranda and Spencer 2005, understanding of electrofisher output). A book, Fishing with Electricity (Cowx and Lamarque 1990), treats the same topics as those in this chapter but in greater detail.