Use of prepositioned areal electrofishing devices with rod electrodes in small streams

We describe the design, performance, and operation of prepositioned areal electrofishing devices (PAEDs) that use rod electrodes for sampling fish in mesohabitat units of a small stream. The flexibility in design offered by rod PAED designs is an improvement over previously reported designs and provides the capacity to specifically match fish immobilization range with varying mesohabitat shape and size under typical field sampling conditions. In our study, immobilization range was determined as the distance from an electrode at which a given voltage gradient (V/cm) resulted in immobilization of several warmwater fish species. For waters with a specific conductivity of about 700 μS/cm, the immobilization threshold was 0.14 V/cm for the 16 species tested. The maximum immobilization range was about 0.85 m when 350 V or more were applied to the rod PAEDs. We evaluated rod PAED performance by considering the effects of electrode length, electrode orientation, and voltage supply on voltage gradients around the electrodes. The results were used to develop general protocols for rod PAED operation. In three scenarios, we documented that electrode placement and voltage adjustment can be used to sample fish in 1.2-16.9-m² mesohabitats at water depths up to 1.3 m. Based on the general protocols developed and outlined in this study, rod PAEDs can be used to quantify fish occupancy in the diverse set of mesohabitats commonly found in small streams.