Effects of Electric Barrier on Passage and Physical Condition of Juvenile and Adult Rainbow Trout

Abstract

Electric barriers can inhibit passage and injure fish. Few data exist on electric barrier parameters that minimize these impacts and on how body size affects susceptibility, especially to nontarget fish species. The goal of this study was to determine electric barrier voltage and pulse-width settings that inhibit passage of larger bodied rainbow trout Oncorhynchus mykiss (215–410 mm fork length) while allowing passage of smaller bodied juvenile rainbow trout (52–126 mm) in a static laboratory setting. We exposed rainbow trout to 30-Hz pulsed-direct current voltage gradients (0.00–0.45 V cm−1) and pulse widths (0.0–0.7 ms) and recorded their movement, injury incidence, and mortality. No settings tested allowed all juveniles to pass while impeding all adult passage. Juvenile and adult rainbow trout avoided the barrier at higher pulse widths, and fewer rainbow trout passed the barrier at 0.7-ms pulse width compared to 0.1 ms and when the barrier was turned off. We found no effect of voltage gradient on fish passage. No mortality occurred, and we observed external bruising in 5 (7%) juvenile rainbow trout and 15 (21%) adult rainbow trout. This study may aid managers in selecting barrier settings that allow for increased juvenile passage.

The Use of Barriers to Limit the Spread of Aquatic Invasive Animal Species: A Global Review

“…Electric fields are used to deter, incapacitate, or kill AIS attempting to pass (depending on voltage and frequency settings, body size, and how far AIS penetrate the electric field). They can be highly effective in blocking some AIS (Savino et al, 2001;Holliman et al, 2015;Layhee et al, 2016), but steel-hulled boats can temporarily disrupt electric fields (Parker et al, 2015), and power outages can be an issue, particularly where AIS accumulate below electric barriers (Parker et al, 2016). For example, despite only suffering 0.001% downtime over a 12year period (due to lightning strikes, power failures, improper maintenance, and equipment malfunction), an electric barrier on the Gila River (Arizona) was breached by several AIS (Clarkson, 2004).…”

“…Electric barriers are generally non-selective and, depending on settings, can result in behavioural deterrence, incapacitation, injury and sometimes even mortality of any native organism attempting to pass (McLain et al, 1965). However, electricity effects do vary with body size so there is potential to provide selective passage by varying voltage and frequency (Layhee et al, 2016) but reducing settings too far will inevitably reduce their effectiveness for blocking AIS (Parker et al, 2015). Chemical barriers are often more target-specific.…”

Retrofitting of Existing Bar Racks with Electrodes for Fish Protection—An Experimental Study Assessing the Effectiveness for a Pilot Site

“…In this context, it is crucial that the fish have a strong sensory perception well above a threshold value of the barrier's stimulus. In case of an electric field used for deterrence, the efficiency depends on the used current and pulse shape, conductivity of the water and of the fish [22], attenuation of the electric field [23], fish species or size and physical condition of the individual [23][24][25]. Since most fish cannot perceive electric fields spatially, the expansion of the field must be great enough to ensure a gradual intensity increase as the fish swim into the field, thereby allowing for an escape reaction into the desired direction away from the barrier [23,26,27].…”

“…Therefore, the perceived body voltage (V) results from the body length (cm) multiplied with the voltage gradient (V/cm) and depends on the orientation of the fish to the field lines [22,29]. Hence, larger fish are more suceptible to electric fields than smaller ones [23][24][25]. Classical electric deterrence systems use two (or more) rows of electrodes in the direction of flow, mainly oriented vertically [3,22].…”

“…Previous ethohydraulic experiments demonstrated the effectiveness of this hybrid fish-protection system [37]. Fish injuries due to the electric field, as mentioned in the literature, mostly occur when the fish is oriented parallel to the field lines in between the electrodes [9,23,24,38]. If a fish passes the barrier investigated in this study, it will not be parallel to the field lines in case of a passage, since it passes parallel to the direction of the flow in between the electrodes, and the duration spent in the zone of high field intensities is also minimized.…”