Use an electric (pulse) trawl
Overall effectiveness category Awaiting assessment
Number of studies: 3
Background information and definitions
Pulse-equipped trawls are mainly beam trawls targeting flatfish (sole/plaice), but also shrimps. The tickler chains are replaced by electrodes that give off short electrical pulses, stunning the fish and raising them off the bottom and making them easier to catch (Polet et al. 2005). It is a highly controversial method and is prohibited in the USA, China and several other countries. It is also technically illegal in EU waters. However, an exception to the rules allows countries to catch up to 5% of their annual fishing quota in the North Sea using "innovative methods" for research, and the use of pulse trawls predominantly occurs here. The Netherlands is the biggest user of this method and in 2018, there were around 80 trawlers holding permits issued by the Dutch government. Despite attempts to ban it altogether, pulse fishing is still ‘allowed’ in EU waters until mid-2021. Many fishers and opposers to the method believe it harms the fish it is designed to catch and kills other marine life (Polet et al. 2005). However, there is evidence that suggests pulse-equipped trawls catch less unwanted marine life, including unwanted fish, than other trawlers (ICES 2020, Polet et al. 2005) and cause less damage to the sea floor (ICES 2020). Furthermore, the body of research assessing the effects of pulse trawling has recently been extended (see references in ICES 2020) and is therefore not within the scope of the current synopsis.
ICES. (2020) ICES Working Group on Electrical Trawling (WGELECTRA). ICES Scientific Reports, 37, 108 pp.
Polet H., Delanghe F. & Verschoore R. (2005) On electrical fishing for brown shrimp (Crangon crangon): II. Sea trials. Fisheries Research, 72, 13–27.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2000 of an area of seabed in the North Sea, off Belgium (Polet et al. 2005) found that electric pulse trawls targeting brown shrimp Crangon crangon reduced the amount of some unwanted and undersized fish caught compared to standard trawls. Of 12 comparisons, catches of undersized commercial fish were lower in pulse trawls than in standard trawls for whiting Merlangius merlangus in four (58–69% lower), sole Solea solea in two (41–60%), plaice Pleuronectes platessa in five (40–80%) and dab Limanda limanda in two comparisons (61–65%). Lower catches in pulse trawls were also reported in non-commercial tub gurnard Trigla lucerna (one of three comparisons), pogge Agonus cataphractus (three of 12 comparisons), dragonet Callionymus spp. (two of 10 comparisons) and goby Pomatoschistus spp. (six of 12 comparisons). Catches of six other non-commercial species were similar in both trawl designs. Catches of legal-sized commercial fish were typically similar in pulse trawls and standard trawls, except for lower catches of flounder Platichthys flesus (29–37%) and dab (17%) in one and two of 12 comparisons respectively. In addition, undersized shrimp catches were reduced in 11 of 15 cases. In 2000, experimental fishing was undertaken on the Flemish Banks off the Belgian coast using two beam trawls simultaneously, a standard trawl and an experimental electric pulse trawl, with pulse generators fitted to the beam of the trawl in one of two array configurations. Fifty-seven hauls were completed with the experimental trawl being towed on one side of the vessel and the standard trawl on the other. Full details of trawl design and generator configurations are provided in the original study.Study and other actions tested
A replicated, paired, controlled study in 2011 in an area of seabed in the North Sea, Netherlands (van Marlen et al. 2014) found that fishing for flatfish using an electric pulse trawl reduced the catches of discarded fish and undersized plaice Pleuronectes platessa and sole Solea solea compared to a conventional beam trawl. Average catch rate of all discarded fish (mainly bottom dwelling species – see paper for data for individual species/groups) was reduced by 57% in the pulse trawl (108 fish/ha) compared to the beam trawl (62 fish/ha). Fewer individuals of smaller sizes of the target species plaice and sole were caught in the pulse trawl than the beam trawl (data reported graphically). Data were collected in May 2011 from 126 trawl by three vessels fishing near each other. Two vessels used different types of pulse equipment (data pooled) and the other was a conventional tickler chain beam trawl (see original paper for specifications). Discarded catch was sampled from 33 hauls from each vessel.Study and other actions tested
A review in 2015 of electrotrawling activity in the North Sea (Soetaert et al. 2015) found that electric pulse trawls reduced unwanted catch, but some damage occurred to fish compared to standard trawls. Unwanted catch was lower in pulse trawls in three cases (30–50% less) and catches of commercial sole were lower in one case (13–22%), compared to using tickler chains. In two cases where electric pulses were used, one in Belgium and one in the United Kingdom, catches of small unwanted sole Solea solea and other small flatfish were lower compared to standard trawls. Cod Gadus morhua, but not lesser-spotted dogfish Scyliorhinus canicula, suffered spinal fractures, other injuries and death at all sizes in one case and only at adult sizes in one case, when fish were close to electric fields (injuries 9–70%, death up to 30%). The review summarised the development of electrofishing using trawls in European waters. Controlled studies (field and laboratory) of the effects of electrofishing on fish were also reviewed.Study and other actions tested