Development and application of electrofishing with towed video as a new survey method for razor clams (Ensis spp.)

Physical and electrical disturbance experiments uncover potential bottom fishing impacts on benthic ecosystem functioning

“…Electrodes seen in flatfish pulse trawling range between 4 and 6 m in length (van Marlen et al, 2014;de Haan et al, 2016) and are towed at speeds of 2.3-2.6 m s − 1 (4.5-5 knots; Poos et al, 2020) limiting the exposure time for a single point in the sediment to a few seconds at most. In comparison, electrodes for Ensis electrofishing are shorter (1-3 m) but are towed at much slower rates (1.5-3.3 m min − 1 ; Breen et al, 2011;Woolmer et al, 2011;Murray et al, 2016;Fox et al, 2019), which allow sediment exposure times of 18-120 s. We thus assigned exposure times of 3-s to represent electrical disturbance from flatfish pulse trawls ('3Bipolar' and '3Direct') while using 120-s exposure times ('120Bipolar' and '120Direct') to simulate sediment exposure periods found in the Ensis electrofishery (stations ES1 and ES2; Table 2). Maximal exposure times were used to assess the effects from 'severe' electrical disturbance from both methods.…”

“…Another electrofishing method uses slow moving electrodes to stimulate razor clams (Ensis spp.) out of their burrows, permitting their collection by divers (Breen et al, 2011;Woolmer et al, 2011;Murray et al, 2016;Fox et al, 2019). This technique has featured both continuous alternating (AC) and direct (DC) currents (Breen et al, 2011;Woolmer et al, 2011;Murray et al, 2016).…”