Electrofishing, which involves a very dynamic and complex mix of physics, physiology, and behavior; has been a valuable sampling technique for over half a century, but its potentially harmful effects on fish must be recognized, monitored, and avoided or minimized, especially with respect to populations of endangered species. Spinal injuries and associated hemorrhages, although often not externally obvious or fatal, can occur anywhere in the electrofishing field at or above the intensity threshold for twitch. These injuries are believed to result from powerful convulsions 0 body musculature caused mostly by sudden changes in voltage. Significantly fewer spinal injuries are reported when direct current, low-frequency pulsed direct current (#30 Hz), or specially designed pulse trains are used. Salmoninae are especially susceptible. Endangered cyprinids of the Colorado River Basin are generally much less susceptible, but the endangered catostomid Xyrauchen Texanus appears sufficiently susceptible to warrant minimal-use policy. Other harmful effects, including bleeding at gills or vent and excessive physiological stress, are also of concern. Mortality, usually by asphyxiation, is a common result of excessive exposure to tetanizing intensities near electrodes or poor handling of captured specimens. Reported effects on reproduction are contradictory, but electrofishing over spawning grounds can harm embryos.

BEHAVIOR OF MARINE FISHES BEHAVIOR OF MARINE FISHES: Capture Processes and Conservation Challenges Understanding fish behavior in relation to capture processes in marine fisheries is of fundamental importance to reducing bycatch and discards, and to enhancing marine fisheries conservation efforts. A thorough understanding of this allows commercial fishers to more effectively capture target species while reducing the catch of unwanted species. Behavior of Marine Fishes: Capture Processes and Conservation Challenges provides the reader with principles, patterns, and characteristics on fish behavior and fish capture processes using several types of important commercial fishing gears. The book also highlights conservation challenges facing the marine capture fisheries in efforts to maintain sustainable use of marine resources and to reduce negative impacts to the marine ecosystem. This volume, with contributions from leading applied fish behaviorists and fishing gear technologists from around the world, will be a valuable reference for researchers, fishing gear technologists, fisheries managers, students, and conservationists. SPECIAL FEATURES: Synthesis of current research and valuable knowledge that will help reduce bycatch and discards in commercial fisheries Review of basic fish behavioral principles and patterns and their relation to capture methods and conservation efforts Contributions from leading international applied fish behaviorists and fishing gear technologists

Summarizes the effects of electrofishing on whitefish, northern pike, and arctic grayling in the Chatanika, Delta and Gulkana Rivers, in Fielding Lake and the Minto Flats area of Interior Alaska and rainbow trout in the Kenai Peninsula, and concludes that this fishing method does not have a substantial detrimental effect on fish populations and causes only minor injury.

Electricity in Fish Research and Management, 2nd Edition provides a comprehensive discussion of the uses of both electricity and electrical principles in fishery management and research. It covers electric fishing (including theory, equipment, data analysis and practical factors affecting efficiency), fish barriers, fish counters and fish welfare issues. The book concentrates on Electric Fishing (or Electrofishing); an internationally accepted and widely used procedure for sampling fish. Over the past 50 years electric fishing has become a standard method for fishery studies and management e.g. establishing population densities and abundance. However, due to the potential hazards of the method (both to operators and fish) there is a continuing need to develop and promote best practice guidelines. The author has studied fish ecology for 40 years and understands the need for information that reaches out to all levels of understanding in the field. Previous books on this subject have either been collections of scientific papers and/or technical reports or very simple instruction manuals. In this book theory and practice is explained using non-technical language and simple equations. It brings depth as well as breadth in both information and principles behind the methods and should be an invaluable tool to both fisheries managers and researchers. Although the book is aimed at undergraduates, the clear explanation of the factors means that the book is suitable for all levels of practitioners.

The purpose of this study was to evaluate the effects of waterborne electric fields on survival of fish embryos. Embryos can be exposed to electric fields during routine electrofishing operations aimed at collecting older fish life history stages to provide data for management of fish populations. Negative effects can occur in fish embryos after electric exposure and this is a particular concern if fish are threatened or endangered species. A primary objective of this study was to develop a model to assist in the prediction of effects of electrofishing on survival of fish embryos. In this investigation, fish embryos were electroshocked over a range of developmental states to determine the most sensitive developmental stage. The most sensitive developmental stage was then used to assess the effect of current type and electric field intensity on survival and induction of premature hatching in electroshocked embryos. Embryos were most affected by electroshock early in development, particularly near epiboly, and DC was more harmful than 60-Hz PDC. At older developmental stages, embryos were less vulnerable to electroshock-induced mortality, and, in some older developmental stages of spotfin chub Erimonax monachus, premature hatching was induced by electroshock. Evidence of premature hatching in other species was inconclusive. Of the species tested, rainbow trout Oncorhynchus mykiss were largest in diameter (4.9 mm) and most sensitive to DC electroshock (lethal voltage gradient causing 50% survival (LV-50) = 1.2 V/cm), followed by whitetail shiner Cyprinella galactura (1.77 mm; LV-50 = 5 V/cm) and spotfin chub (1.83 mm; LV-50 = 6 V/cm), which were similar in size and sensitivity. A strong relation between embryo diameter and vulnerability to electroshock-induced mortality was found when results from the present investigation were combined with similar results from the literature. Results support use of embryo size as a predictor of vulnerability to electroshock in other species, and indicate that species with large embryos may be particularly vulnerable to lethal effects of electrofishing.