Pulse Trawling

Pulse trawling is a technologically advanced – and highly controversial – method of commercial fishing which has only been used on an experimental basis up until now, but appears to be on the verge of making a major breakthrough into mainstream industrial fishing.

Pulse Trawl

Diagram of a pulse trawl in action.

Pulse trawling is an adaptation of beam trawling, a method of commercial fishing which has been used for over one hundred years. Beam trawling is used to catch demersal species (those that live and feed on or near the seabed). The mouth of the net is held open by a solid metal bar and up to twenty ‘tickler chains’ trash the seabed in front of the net to stir up fish (especially flatfish which bury themselves under the sand and silt of the seabed) which then allows them to be scooped into the net. Pulse trawling replaces the tickler chains with a series of electrical drag wires mounted into the net. These wires send an electrical pulse around the net which shocks and stuns fish out of the ground and moves them into the net (1) .

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The pulse trawling system was invented by in the Netherlands by Piet Jan Verburg in 1992. The Dutch have remained the biggest proponents of pulse trawling and have advanced the use of this technology claiming that pulse gear has less contact with the seabed meaning that there is more of the target species caught, less bycatch, less damage to the seabed and fish that are caught have less damage done to them and therefore reach a higher price at market. Furthermore, and the point that is of most interest to commercial fishermen, since pulse trawls do not have heavy tickler chains they are much lighter than beam trawl nets, meaning that fishing with pulse gear uses up to 40% less fuel than traditional beam trawling (1), (2) . Although it costs on around £300,000 to convert a beam trawler to a pulse trawler and retrain the crew to use the new equipment, the savings that can be made mean that this investment can soon repay itself.

Burrowed flatfish

Flatfish which bury themselves under the sand, such as this brill, are the target of pulse trawlers.

However, the evidence of pulse trawls that have been used in the real world does not bear this out. Pulse trawling was used extensively in the East China Sea in the 1990s to catch shrimp. By the year 2000 there were around 10,000 beam trawlers working the area, 3000 of which were equipped with pulse trawling gear (3). Catches of all kinds of shrimp, especially the burrowing species of shrimp, began to go up. However, lack of regulation meant that different levels of power were being used in the pulse gear, and it soon became apparent that damage was being caused to both juvenile shrimp populations and other benthic species (those that live in the seabed itself such as crabs, shellfish and starfish) (3), (4) . Pulse trawling was therefore banned in the seas around Zhejiang Province which had previously been the most popular area for pulse trawling, and the rest of the East China Sea soon followed (3) .

The European Union has also been wary of allowing pulse trawling. In 2007 a number of pulse trawlers have been allowed to operate but only on an experimental, and highly regulated basis. The Dutch fishing industry lobbied to allow greater freedom to use pulse and electrical trawling gear and in 2010 they were partially successful in getting the restrictions on pulse trawling eased – a maximum of 5% of the Dutch commercial fishing fleet was allowed to use electrical fishing gear. This may seen like a small rise but it meant a quadrupling of the number of pulse equipped vessels.

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Due to Europe’s Common Fisheries Policy (CFP) these pulse trawlers were now permitted to operate within twelve miles of England’s coastline and fishermen working out of ports in Essex and Kent certainly do not agree with the Dutch view that pulse trawling is a clean, safe and environmentally responsible way to catch fish. Reports began to emerge that masses of dead Dover sole were being brought up in the British trawler’s nets and the number of live and healthy flatfish, particularly sole, had declined dramatically. In an article in the Sunday Times the fishermen directed the blame squarely at the Dutch:

             [It’s like] “fishing in a graveyard…What they don’t catch they annihilate…Virtually everything is dead.” – Tom Brown, Secretary of Thanet Fisherman Association.

             “This is absolutely devastating for us because we never caught so many fish that [were] already dead…It’s a waste of time going to that area now. It stinks of dead fish.” – Jeff Loveland, owner of two fishing boats operating out of Ramsgate, Kent.

             “I have fished there for 30 years and never seen anything like it. I think the pulse is killing the food in the seabed. Three years ago I caught 40 tons of sole in those grounds in one year. It was the best year we’ve ever had. There is nothing there now that I can catch.” – Roger Free, commercial fisherman from West Mersea, Essex.

A study into pulse trawling by the ICES (International Council for the Exploration of the Sea), which, it must be noted, the Dutch commissioned, backed up the claims of the British fishermen. The study found that cod which were close to the pulse trawl gear (but not caught in the net) suffered from cracked vertebrae and internal haemorrhaging, and pulse trawling has the potential to increase mortality rates in cod, although more research was needed (5). The study went on to say that less fuel was used by vessels using electric gear, and there was a lower bycatch of benethic species. However, it was also stated that “There are indications that the gear could inflict increased mortality on target and non-target species that contact the gear but are not retained” (5), and the study warned that pulse trawling in the real world could have a significantly different impact on the marine environment than they predicted (5). Further research was advised and it was stressed that pulse trawling should only continue on a limited scale and in a highly regulated way (5).

As it stands pulse trawling is still fairly rare. However, with the Dutch fishing industry pushing hard for greater acceptance of this technology, and fishermen all over Europe attracted by the lower fuel costs and better quality catch, it appears that pulse trawling could quickly become much more widespread. Some commercial fishing companies believe it is only a matter of time before pulse trawling becomes more common than traditional beam trawling (6). It remains to be see what consequences this will have on Europe’s fish populations and the wider marine ecosystem.

References:

1. Pulse Trawling – Ecomare.nl.
2. Pulse Trawling – zeeinzicht.nl.
3. Yu, C., Chen, Z., Chen, L., and He, P. (2007) The Rise and Fall of Electrical Shrimp Beam Trawling in the East China Sea: Technology, Tishery, and Conservation Implications. – ICES Journal of Marine Science, Issue 64.
4. Zapped: Britain’s Fishing Graveyard – The Sunday Times 24/6/12
5. The Answer to the Netherland’s Request on Electric Pulse Trawl – ices.dk.
6. Pulse Trawl – Orion Fishing.

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