Background and Justification
Electrofishing is a valuable sampling technique for population assessment of threatened and endangered fishes, but it is frequently prohibited by management agencies in waters where such fishes occur to avoid the risk of fish injury or mortality. We quantified electrofishing injury and short-term mortality of the Cape Fear shiner, Notropis mekistocholas, a federally-listed endangered fish known from only five populations in the Cape Fear drainage, North Carolina, and the spotfin chub, Cyprinella monacha, a threatened species extant in several southern Appalachian Mountain drainages. The availability of hatchery-reared stocks of these rare fishes made this research possible.
Objectives and Methods
Groups of hatchery-reared Cape Fear shiners and spotfin chubs were exposed to different alternating and direct current voltages (140, 240, or 340 V), pulse rates (AC, DC, 60, or 120 Hz), and exposure durations (3, 6, 12, 24, 48 sec) in a series of controlled experiments. The predominant behavioral response elicited in experimental groups of 18-21 fish was categorized as escape, loss-of-equilibrium, or immobilization as a measure of treatment effectiveness. Experimental and control groups were monitored for 36 hours post-treatment to determine short-term mortality. Electrofishing injury was assessed in treated fish via dissection and examination under a dissection microscope. Additionally, dorso-ventral and lateral radiographs, using mammography film and intensifying screens, were made of surviving and dead fish.
Results and Implications
Preliminary results suggest that these threatened and endangered minnows may be sampled by electrofishing with minimal injury or mortality when appropriate wave forms are used. However, the risk of such minimal mortality may or may not be acceptable to management agencies for these species. Further, laboratory exposures transferred more energy than necessary for fish immobilization in some treatments, and such experimental voltages are not directly transferable to field situations. Thus field voltages should be based on fish response, and field operators should minimize voltage to threshold levels, based on fish response.
For details of results see
Holliman, F.M., J.B. Reynolds, and T.J. Kwak. 2003. A predictive risk model for electroshock-induced mortality of the endangered Cape Fear shiner. North American Journal of Fisheries Management 23: 905-912.
Holliman, F.M., J.B. Reynolds, and T.J. Kwak. 2003. Electroshock-induced injury and mortality in the spotfin chub, a threatened minnow. North American Journal of Fisheries Management 23: 962-966.
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