Unintended Effects of Electrofishing on Nongame Fishes

Abstract

Most studies of injury associated with electrofishing have focused on game fishes, but few have given attention to cohabiting small nongame species. Under controlled laboratory conditions, we subjected small nongame cyprinids, ictalurids, and percids to a wide range of voltages and waveforms to examine potential harmful effects. Fish were treated with power levels distributed uniformly between the thresholds required to immobilize game fish and also were subjected multiple times to those thresholds to simulate the range of conditions that might exist in a heterogeneous electrical field formed during electrofishing in field situations. Across waveforms and species, the incidence of hemorrhages averaged 2% (range = 0–20%), the incidence of spinal injuries averaged 6% (range = 0–30%), and mortality averaged 16% (range = 0–90%). Continuous DC was generally less harmful than pulsed‐DC waveforms; hemorrhages and spinal injuries tended to increase with high pulse frequencies, and mortalities tended to increase with low pulse frequencies. Ambiguities in the results were apparent, suggesting that some species may experience extensive harm, whereas others may not. Given the potential to harm numerically small populations and populations of imperiled species, we suggest (1) expanded efforts to overcome the power limitations that prevent effective use of continuous‐DC electrofishing in many field situations and (2) pilot studies at geographic locations where numerically small populations of nongame species may be a concern.

Side-effects of electrotrawling: Exploring the safe operating space for Dover sole (Solea solea L.) and Atlantic cod (Gadus morhua L.)

“…This accords with previous experiments in which fish was exposed below immobilization threshold (Dolan and Miranda, 2003), but differs from studies in which fish, forced into cramp, were often found with mortality rates ranging from 0 to 30% (De Haan et al, 2009b;Dolan et al, 2002;Dolan and Miranda, 2004;Schreer et al, 2004;Sharber and Carothers, 1988;Sharber et al, 1994). However, as the rates of mortality and injuries are not always directly related (Dalbey and Mc Mahon, 1996;Dolan et al, 2002;Dolan and Miranda, 2004;Miranda and Kidwell, 2010), the exposed animals were further examined for external and internal as well as macroscopic and microscopic injuries.…”

Electrotrawling: a promising alternative fishing technique warranting further exploration

“…Crappies showed spinal injuries at 5, 60 and 110 Hz but haemorrhaging was higher at 60 and 110 Hz, and mortality was only seen at 5 Hz (Dolan 2002). This was confirmed by Miranda and Kidwell (2010), who concluded that the mortality of the warm freshwater non-game test species was not related to gross-scale injuries because similar or worse haemorrhages and spinal injury were seen in fish that survived electroshock and those that died. This finding suggests that the mechanisms causing physical injuries are not the same as the mechanisms that cause immediate mortality.…”

Gear effectiveness and size selectivity for five cryptic madtom species ( Noturus spp.)

“…Electrofishing is one of the most common methods for ecological monitoring in wadeable streams, but is occasionally avoided due to increased potential for mortality of threatened and endangered species (Henry, Grizzle, Johnston, & Osborne, ; Miranda & Kidwell, ). Electrofishing was generally the most efficient gear for detecting madtoms similar to related research (Poos, Mandrak, & McLaughlin, ; Pygott, O'Hara, Cragg‐Hine, & Newton, ; Wiley & Tsai, ), but like each other gear type, generally represented fish size structure poorly.…”