Effect of electrical stimulation used in the pulse trawl fishery for common sole on internal injuries in sandeels

Abstract

Electric stimulation was used in the North Sea beam trawl fishery for common sole to reduce its environmental impact. Because electrical stimulation may cause internal injuries in fish, a laboratory experiment was conducted to study the effect of pulse exposure on lesser sandeel (Ammodytes tobianus) and greater sandeel (Hyperoplus lanceolatus), important mid-trophic species in the North Sea ecosystem. We exposed 244 sandeels between two electrodes to a pulsed bipolar current for 2 s in an experimental cage with 5 cm sediment; 221 control fish were handled similarly but not exposed. The occurrence of spinal injuries and internal haemorrhages were scored using X-radiography and dissection. None of the sandeels exposed to a field strength of up to 600 V m–1 showed spinal injury or haemorrhage. Equal numbers of minor spinal abnormalities were found in exposed and control fish. In the absence of spinal injuries, we estimated by bootstrapping the field strength below which spinal injuries are unlikely to occur, i.e. the lower limit threshold, and the corresponding limit dose–response relationship between field strength and injury probability. We conclude that it is unlikely that pulse trawl fishery will have an ecologically significant adverse effect on the population abundance of sandeels, because of the low probabilities of exposure and injury.

A Transdisciplinary Approach Towards Studying Direct Mortality Among Demersal Fish and Benthic Invertebrates in the Wake of Pulse Trawling

“…Because the recorded injury rate in pulse trawl catches was low (<2.5%) in 14 dominant North Sea fish species sampled (Boute, 2022;Boute et al, 2022) it is highly unlikely that pulse-induced internal injuries will result in mass mortality. This conclusion also holds for the two species (cod, sandeel) for which higher injury rates were observed, because cod is only a small fraction of a beam trawl's catch (ICES, 2020), and because none of the sandeel exposed to a commercial pulse stimulus in a tank experiment developed internal injuries (Schram et al, 2022).…”

Electrotrawling can improve the sustainability of the bottom trawl fishery for sole: a review of the evidence

“…Sandeels were exposed to a pulse stimulus for 2 s in an experimental cage with 5 cm sediment (Schram et al 2022b). The field strength varied 20 and 640 V m -1 , depending on their positions relative to the electrodes.…”

Behavioural response thresholds of marine fish species for pulsed electric fields

“…Furthermore, Abrantes et al (2021) tested the effect of electric fields on largetooth sawfish (Pristis pristis) behaviour and reported reaction distances of <1.2 m to the electrodes but did not quantify the electric field strengths and worked with different electrical waveform characteristics. Few studies have examined the behavioural response of marine fishes to low electric field strengths as the focus has generally been on galvanotaxis/electrotaxis (Bary, 1956;Diner and le Men, 1971;Klima, 1972;Diner and le Men, 1974;Polet, 2010;D'Agaro, 2011), immobilising whole-body muscle contractions referred to as electronarcosis, tetanus, or cramp (Bary, 1956;Diner and le Men, 1971;Diner and le Men, 1974;Stewart, 1977;Polet, 2010;de Haan et al, 2016), and (internal) injuries (van Marlen et al, 2014;de Haan et al, 2016;Desender et al, 2016;Soetaert et al, 2016a;Soetaert et al, 2016b;Soetaert et al, 2016c;Soetaert et al, 2018;Boute, 2022;Boute et al, 2022;Schram et al, 2022;Boute et al, 2023). Bary (1956) studied 'minimum response values' based on body jerks (also referred to as muscle twitches) during stimulation in golden grey mullet (Chelon auratus), European flounder, and European seabass of different body lengths, but in a homogeneous electric field with waveforms different from those used in pulse trawling for common sole.…”

“…Common solethe target species for pulse trawlersresponds to high field strengths by curling their body upwards in a U-shape during which they are immobilised, without obvious damage (Soetaert et al, 2015b;Soetaert et al, 2016b). Whole-body muscle contractions in non-target species, especially bilaterally-symmetrical round fish, may however lead to spinal injuries and internal haemorrhages, as studied in the laboratory (de Haan et al, 2016;Soetaert et al, 2016a;Soetaert et al, 2016b;Soetaert et al, 2018;Schram et al, 2022) and under field conditions (van Marlen et al, 2014;Soetaert et al, 2016c;Boute, 2022;Boute et al, 2022;Boute et al, 2023). Whole-body muscle contractions occur at field strengths above 37 V m -1 in Atlantic cod (Gadus morhua) resulting in a 50% spinal injury probability in larger specimens at 80 V m -1 (95% CI: 60-110 V m -1 ) (de Haan et al, 2016).…”