Fishing by electrocution

23rd February 2018

Electric pulse fishing (also known as electrofishing or electrical trawling) is a trawl fishing technique used in Europe to target flatfish (sole) and shrimp.  It involves the release of electric currents with a range of frequency, voltage, pulse polarity, pulse shape, and pulse duration combinations into the seabed to either immobilize fish so they do not try to escape the fishing net or to startle them to jump into the fishing net.  Traditional beam trawlers drag bobbin rope or tickler chains along the seabed to push finfish or shrimp up and into the path of the fishing net.

On ‘Electro-trawlers’, these gears are replaced with a number of electrodes, attached to the gear in the tow direction, that emit electric pulses. There are two basic types of pulses depending on the target species. Vessels targeting fish like Dover sole use a bipolar pulse of around 80Hz to induce cramping in the fish that immobilizes them and stops them from escaping the trawl net. While vessels that go after shrimp tend to produce unipolar pulses of around 5Hz that startle the shrimp and induce an involuntary tail-flip that causes it to jump up from the seabed into the net.

Watch the video below to learn more about how electric pulse trawling works.

On the surface, electrofishing might seem like the ideal, environmentally friendly fishing method.  The gear used islighter than some gear used in conventional beam trawling and consumes up to 50% less fuel to tow making it more economical. It also appears to be more selective. An average by-catch reduction of 35% in volume was observed during extensive commercial testing of the prototype. The trial also indicated that contact with the seabed was reduced by 75% while catch efficiency was maintained.

This method of fishing has been banned in the European Union (EU) since 1998 due to uncertainty about its impact on non-target marine organisms and ecosystems that may be exposed to its effects. However, since 2009 an exemption in the legislation has allowed EU member states to electrofish using 5% of their beam trawl fleet in the southern North Sea, and this was increased to 10% in 2014. In addition, some members states have increased their electrofishing capacity under the guise of conducting scientific trials to test fishing methods that avoid, minimise or eliminate fishery bycatch. In 2016 approximately 91, mainly Dutch and British, trawl boats were commercially electrofishing in this region.

However there is growing concern that electric pulse fishing may not be as sustainable as it is touted to be by some quarters. Studies on adult Dover sole and Atlantic cod have shown that the response of fish during and after exposure to electric pulses can range from a straightforward escape response at low electrical loads, to cramp reactions at medium electrical loads and tonic-clonic epileptic seizures, spinal injury and haemorrhaging in cod at high electrical loads.

Further, fishers in the southern North Sea have been reporting that since the industrial scale ramping up of electric pulse fishing in the area they have seen a drastic reduction in the key target species, sole, cod and seabass. They are also reportedly hauling large amounts of already dead fish and observing dead shellfish, starfish and small fish in areas fished by electro trawlers, so much so that they have started referring to the southern North Sea as the dead zone.

In January this year, French fishers blockaded the busy port of Calais to protest over the damaging impact that electric pulse fishing is having on fish numbers and their livelihood. Amid such heated protestation and controversy, on 16 January the EU parliament voted to ban electric pulse fishing in its waters. This ban is yet to be confirmed as decisions have to be negotiated with the European Commission and members states prior to being final but the EU parliament’s resolve has concerned the mostly Dutch fishers that have heavily invested in adopting the technology.

The final outcomes of this saga may not be fully known for some time but if nothing else, this is a cautionary tale on the perils of unleashing on the environment technologies that may on the surface seem sustainability-friendly but are not sufficiently supported by rigorous scientific testing and evidence. What seems to have happened in the southern North Sea is that electric pulse fishing has resulted in the trawling and, potentially destruction, of benthic habitats that used to provide sanctuary to feeding and juvenile fish by virtue of their inaccessibility to conventional beam trawlers.

Electric pulse fishing is not an allowed method in the South East Trawl Fishery.    Conventional bottom trawling attracts criticism for its environmental impacts but Australian and international research has shown that its impact on the environment is less than many allege.  Bottom trawling in south east Australia is aggregated into small areas due to closures or due to grounds being unproductive or too rough for the fishing gear.  Research in the south east has found that only 6% of the seafloor is every touched by trawl gear and that bottom dwelling invertebrates populations are at  80-93% of their un-trawled abundance and continue t increase.

Read more.

*Featured image is by Wageningen UR.

Links to reports on electrofishing.

ICES working group report

IMARES research institute webpage on pulse fishing

an article in “The Conversation” by Mike Kaiser:

Science Mag article: