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

Abstract

Electrotrawling is currently the most promising alternative for conventional beam trawls targeting sole and shrimp, meeting both the fisherman’s aspirations and the need for more environmentally friendly fishing techniques. Before electrotrawling can be further developed and implemented on a wider scale, more information is needed about the effects of electrical pulses on marine organisms. Adult Dover sole (Solea solea L.) and Atlantic cod (Gadus morhua L.) were used in the present study as model species for flatfish and roundfish, respectively. These animals were exposed to homogeneously distributed electrical fields with varying values of the following parameters: frequency (5–200Hz), electrical field strength (100–200V/m), pulse polarity, pulse shape, pulse duration (0.25–1ms) and exposure time (1–5s). The goal was to determine the range of pulse parameters which can be regarded as safe and thereby also to evaluate the effect of the pulses already being used in commercial electrotrawls. Fish behaviour during and shortly after exposure, 14-days post exposure mortality rates, as well as gross and histological examination were used to evaluate possible effects. During exposure, both species showed an escape response below a frequency of 20Hz and a cramp reaction above 40Hz. These reactions were immediately followed by post-exposure escape behaviour and at high electrical loads cod showed tonic-clonic epileptiform seizures. No mortality was observed and histological examination did not reveal any abnormalities, except for one cod showing a spinal injury. These data reveal the absence of irreversible lesions in sole as a direct consequence of exposure to electric pulses administered in the laboratory, while in cod, more research is needed to assess cod’s vulnerability for spinal injuries when exposed to the cramp pulses.