In-depth analysis of ICES’ advice on electric fishing

The Netherlands have requested a special advice from ICES to “compare the ecological and environmental effects of using traditional beam trawls or pulse trawls when exploiting the TAC of North Sea sole“. Although this advice was based on already published reports — adding nothing to the ongoing and intense debate on electric fishing — Dutch lobbyists and politicians have been eager to use it to avoid a full ban on electric fishing in the coming weeks.

Below, we go through this advice and explain why this is nothing but shameless instrumentalization of science.

A crooked question to make electric fishing “great again”

The request from the Netherlands was designed to insinuate doubts as it requested a comparison of electric fishing with one of the most destructive fishing gears there is. Although this question could only result in a positive outcome — given the poor quality of the research that was conducted — being ‘better’ than the worst fishing gears certainly does not make electric ‘good’, let alone ‘sustainable’. If we were to choose between the guillotine and the electric chair, we would simply answer that we are against death penalty. Should electric trawling have been compared to more virtuous alternatives to catch flatfish in the North Sea (such as gillnets), ICES conclusions would have been radically different.

This trick has been repeatedly used by the Dutch industrial lobby, which keep referring to electric fishing as the only alternative to beam trawling. As the French chapter of the LIFE platform (Low Impact Fishers of Europe) put it, the fact that ICES has accepted to answer this very biased question is nothing short of shameful, especially during a crucial period of the Trilogue negotiations.

Known harmful impacts, substantial uncertainties and many unknowns

Physical impact on adult fish

ICES highlights that “cod suffer a relatively high injury rate when exposed to pulses, but the increase in the overall mortality of the North Sea cod stock caused by these injuries is presently negligible“. ICES further explains that “most injuries occurred in sizes of fish that would be retained by the gear and would be killed anyway“! Let’s rephrase: electric shocks are everything but benign, as they result in many cod having their spine broken. So how could we possibly imagine that these ‘pulses’ do not severely impact any other marine life such as other fish species, juveniles, shrimp, or ragworm? These lethal impacts are reported by every single small-scale fishers in the North Sea, who speak of ‘graveyards’ in the wake of electric trawlers. The same small-scale fishers that are astonishingly unaccounted for by ICES in its advice, although they represent 82% of European fishing units.[1]

Physical impact on the seabed

ICES boldly asserts that “pulse trawls do not mechanically penetrate as deeply into sediments as traditional beam trawl and will therefore have a lesser mechanical effect on the benthos“, and that “pulse trawls have a reduced footprint“. Although this is somewhat true, there are two major issues that render these conclusions awfully biased:

  • The first issue is that the study on which this statement is based is spurious. Researchers estimated that — on small experimental trawls (4.4 m wide) — electrodes still penetrate 5 mm into the sediment while the trawl shoe reaches 6 cm into the seafloor.[2] However, commercial trawls generally reach a width of 12 meters,[3] so their physical impact is probably much higher. What is more, the scientific protocol that was used to assess these physical impacts is highly questionable, given that instead of measuring the impact right after the passage of the trawler as should have been done (shallow, highly dynamic waters), Dutch scientists assessed the impact of regular beam trawls 12 to 44 hours after their passage and 55 to 107 hours for electric trawlers, thus creating data which do not match rigorous scientific standards and cannot even be compared within the same study! The fact is: the seafloor is impacted in both cases. Furthermore, as noted in the longer report by the ICES working group on electric fishing (WGELECTRA), the most superficial part of the seafloor is the one that hosts the most biodiversity, so going less deep than not mean that the impact is reduced anyway.
  • shift in fishing effort due to electric fishing

    Distribution of fishing effort for ‘regular’ (left) and electric ‘pulse’ trawlers in the North Sea. Source: LIFE platform.

    The second issue is that electric trawls being lighter than the extremely heavy beam trawls, they can operate in coastal areas that were previously inaccessible to them due to their softer grounds. WGELECTRA notes that “the fleet of pulse licence holders changed their spatial distribution towards southern and western fishing grounds when switching from beam trawls to pulse trawls. Absolute fishing effort increased on local fishing grounds along the Belgian coast (within 12 nm zone) and off the Thames”. These areas, which are often reproduction zones or nurseries for numerous marine species, were previously only fished by small-scale, low impact fishers. Thus, given than regular beam trawls were excluded from these essential habitats, pleading that electric fishing has a lower physical impact or that its footprint is reduced is simply nonsense.

Interestingly, WGELECTRA notes that “electric fields […] may penetrate into the sediment potentially affecting benthos that live below the penetration depth of tickler chains. The effects of pulse exposure are not yet fully understood and the combined effects have not been studied yet“.

Impact on benthos

ICES concludes that “incremental effects from repetitive exposure to pulse gear are expected to be low“, and that “the limited evidence indicates that invertebrates in the track of the trawl show no detectable effects of electrical stimulation“. In that case, why would Dr. Adriaan Rijnsdorp — one of the most active scientists working on electric fishing, and co-chair of ICES’ WGELECTRA — publicly acknowledge that “if you start [taking seabed samples] right away, you will only find dead animals so we take samples two days later“.[4]

Noteworthy, ICES concedes that “there are no specific studies on the non-lethal effects of electrical stimulation from pulse trawls on invertebrates“, and it is noted in WGELECTRA’s report that “there are only three studies which have attempted to examine the direct mortality imposed by pulse trawls“.

Impact on electro-sensitive species such as shark

ICES reports that “there is some evidence showing that the ability of the small-spotted catshark […] to detect prey using its electrosensitive sensory system was not significantly affected after being exposed to a sole pulse“. To support this outrageous statement, ICES uses two studies[5],[6] (one of which used shrimp pulse electrical parameters) whose goal was to demonstrate if electricity had an impact on the ability of sharks to feed thanks to their electrosensitive sensors (which they use to hunt and navigate). In both experiments, specimens did not need to hunt for food, so although their conclusions are that there is no proven impact, the protocol did not allow the measurement of such impact! This criticism was partly formulated by ICES for the first study: “these dogfish offered sardine as a food under quite simple foraging conditions, where the sharks could find the food items without any electro-receptors. Ideally, special experiments are needed to show that electroperceptive system still works in elasmobranches exposed to a strong electric field”.[7] For the second, much more recent study, the situation was quite similar with sharks placed in small tanks, not necessitating to hunt and subjected to a single electrical impulse. Finally, the species used in both cases — the small-spotted catshark — is known to be extremely resistant and thus not the most appropriate species to measure a sensitivity to anything…

Impact on bycatch

ICES notes that “a substantial fraction of the catch of these fisheries is discarded, but this may change with the implementation of the EU landing obligation by January 2019. The extent of the change will depend upon the degree of compliance with the landing obligation or if there are exemptions from the landing obligation, e.g. due to high survival rates of discarded fish“.

High survival rate? They were measured for several discarded species and were very low, especially for undersized specimens: 15% for plaice, 29% for sole, and 16% for dab (these survival rates do not account for post-release mortality by birds, fish etc.).[8] However, scientists recognized that the conditions in which they conducted the experiment were “mild compared with [parameters] that are typical for the majority of the beam-trawl fleet in the North Sea“.[9] Thus, survival rates would be even lower during commercial activities.

We would also like to emphasize that although “ICES considers that pulse trawls could contribute to a technical solution to some problems emerging during the implementation of the landing obligation, as the catchability of sole is higher in this gear (the more valuable but rarer species) and that of plaice is lower (the less valuable but more abundant species)“, the aim of the landing obligation is not to increase the catch of high value species, but their marketable size. On that matter, ICES acknowledges that “it is uncertain whether the pulse trawl has improved the size selectivity, e.g. catching fewer undersized fish relative to larger sized classes of the same species.” Not knowing the size selectivity of the electric gear after more than 10 years of ‘research’ is rather surprising…

Impact on reproduction, eggs and juveniles

ICES argues that “there is no information available on the survival of fish at early life history stages after exposure to the sole pulse. Experiments with a pulse of a lower frequency than that used for sole (5Hz) suggest that certain larval stages of cod, but not of sole, show higher mortality when exposed to field strengths occurring in close range of the conductor. No effect was found for egg stages.”

There are two studies that used shrimp electric pulses (lower frequency and less harmful unipolar current) on eggs and larvae from cod and sole. The first one showed a hatching rate delay on cod and a higher mortality for two larvae stages. The second one is a sham, as explained in our news article.

Noteworthy, ICES acknowledges that “no studies have been conducted to investigate the possible adverse effects of sub-lethal exposure on the maturation process, the quality of gametes, or spawning behaviour of any fish species.

Impact on water quality

ICES boldly asserts that although “electrolysis can cause the formation of chlorine gas (Cl2) in saltwater […] there is no evidence suggesting that sole pulses lead to electrolysis“. This statement is based on preliminary experiments. In the latest report by WGELECTRA, it is explained that “additional laboratory experiments were carried out to see if the release of Cl2 gas led to the formation of hydrochlorous acid and subsequent changes in pH. After 10+ minutes of constant pulsing, no changes in pH occurred when using commercial sole or shrimp“. Ten minutes, whereas commercial activities last as long as four hours.

Furthermore, although the same report explains that “when parameters were adjusted to exhibit a pulsed direct current (PDC) at a high frequency (90 pulses per second), visual formation of Cl2 gas bubbles was observed along with a corresponding drop in pH confirming the potential for electrical pulses to exhibit electrochemical reactions under certain conditions. Nevertheless, there is currently no evidence showing that commercial pulse parameters lead to effects related to electrolysis“. In essence, researchers observed the formation of toxic compounds when modifying the parameters of a shrimp electric trawl, but “there is currently no evidence showing that commercial pulse parameters lead to effects related to electrolysis“? Bear in mind that, according to ICES, “the existing regulatory framework is not sufficient to prevent the introduction of potentially damaging systems“.[10]

Impact on fuel consumption

Lastly, ICES notes “that pulse trawls use 46% less fuel than traditional beam trawls per hour of fishing“, which has been one the the main arguments of the electric lobby during our campaign. It has a “positive impact on the climate“.[11] However, we have shown that is argument was a fraud: an electric trawler consumes 2.21 litres of fuel per kilo of fish caught, whereas a beam trawler consumes 2.36 l/kg.[12] The reason electric trawlers consume less fuel in volume per year is because they manage to catch their sole quota much faster thanks to the efficiency of the gear. But ‘sustainability’ has nothing to do with ‘efficiency’, on the contrary. The fact that ICES mistakes the two is very disturbing and speaks volume of the quality of their advice.

Notes and references

[1] European Commission (2016) Small-scale coastal fleet in the EU. European Commission, Brussels (Belgium). Available at:

[2] Depestele et al. (2016) Measuring and assessing the physical impact of beam trawling. ICES Journal of Marine Science 73(suppl_1): i15-i26.

[3] Haasnoot et al. (2016) Fishing gear transitions: lessons from the Dutch flatfish pulse trawl. ICES Journal of Marine Science 73(4): 1235-1243.

[4] Brouwers (2018) De schrik, kramp en shock van de gepulste vis., edition of January 26 2018.

[5] de Haan et al. (2009) The effects of pulse stimulation on biota — Research in relation to ICES advice — Effects on dogfish. Report number C105/09 Institute for Marine Resources and Ecosystem Studies (IMARES), IJmuiden (The Netherlands). 32 p. Disponible à :

[6] Desender et al. (2017) Pulse trawling: evaluating its impact on prey detection by small-spotted catshark (Scyliorhinus canicula). Journal of Experimental Marine Biology and Ecology 486: 336–343.

[7] ICES Advice 2009, Book 1, p4. Disponible à :

[8] van der Reijden et al. (2017) Survival of undersized plaice (Pleuronectes platessa), sole (Solea solea), and dab (Limanda limanda) in North Sea pulse-trawl fisheries. ICES Journal of Marine Science, 74(6): 1672–1680. High bycatch and low survival rates can be guessed from this video taken aboard F/V TX-19:

[9] Uhlmann et al. (2016) Injury, reflex impairment, and survival of beam-trawled flatfish. ICES Journal of Marine Science 73(4): 1244-1254.

[10] ICES (2016) Advice 2016, Book 1. Request from France for updated advice on the ecosystem effects of pulse trawl.

[11] See e.g. the “Care for the climate” website:

[12] Factsheet pulse fishing 204. Available at:

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