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Flying Trawl Doors: A Better Way to Fish

By Malin Skog, SFPO

The Swedish Fishermen’s Producer Organisation (SFPO)’s ongoing collaboration with the Swedish University for Agricultural Sciences (SLU) has expanded its remit, now investigating gear that is designed not only for selectivity but also for low environmental impact. They have been testing flying trawl doors, potentially a big step forward in gear innovation. They are designed to minimise the impact on the environment and save on fuel, whilst maintaining the same levels of catch compared to conventional trawl doors. SFPO’s Sustainability Manager Malin Skog explains more.

Flying Trawl Doors – Why They’re Special

As their name suggests, these doors ‘fly’ 2-4 metres above the seabed. Flying trawl doors were inspired by the aerofoil of aircraft – the unique shape drives a cushion of air or water beneath the ‘wing’, creating lift from below. Any weights needed to keep the front of the trawl close to the sea floor when the doors are lifted,  are integrated into the wires and ropes and can be adjusted so that the doors are suspended at the optimal depth for the fishery in question.

Conventional trawl doors are often criticised for the deep furrows they carve in the seafloor sediment. These can damage the seabed ecosystem and create sediment plumes that can muddy the waters.  The flying trawl doors can be monitored and adjusted in real time to ensure they never touch the seabed, so this negative effect is removed.

Furthermore, flying trawl doors are also much better for fuel use. Dragging conventional trawl doors along the seabed naturally creates resistance, but by suspending them above the seabed this resistance is greatly reduced. This is not only better for fishermen’s pockets but also lessens exhaust emissions.

Results Are Promising

We have been working together with SLU to validate the data, and the first set of results have been very positive. Fuel consumption was reduced by 10-25%, whilst fishing ability appeared to not be compromised at all. Catches of prawn (Pandalus) and Nephrops were equivalent to those caught by conventional trawls.

Of course, there are always teething problems, and a few days’ grace helps the fishermen get used to the new gear and make minor bespoke changes before daily catches reach conventional levels. But after this initial adjustment period, fishermen’s responses have been principally positive: skipper Niklas Hallberg says they “had no problems, the doors kept their distance from the bottom and they were very easily adjusted and stable”.

The Importance of Collaboration

Since 2014, SLU has been running a national programme together with the fishing industry (SFPO and others) to develop selective gear in order to comply with the Landing Obligation. Since fishermen see first-hand the issues that fisheries face, they are in an ideal position to suggest changes. The scientists at SLU can then look into design, trialling and data analysis. In 2018, the programme’s scope was widened to include environmentally friendly gear in addition to selective gear.

The funding is channelled via SWAM (Swedish Authority for Water Management). This works out better for fishermen than EMFF funding because they can be compensated for their involvement. For instance, if a gear trial results in a below-average catch, the fishermen involved receive compensation to bring their daily profit up to their average amount. If a gear trial results in an above-average catch, however, then the fishermen naturally receive an above-average profit and no compensation.

Looking into the Future

SFPO has several sets of flying trawl doors that fishermen are testing out in a number of fisheries. The project is still in an early stage (beginning in Autumn 2018), but we hope that once the positive results become more widely known, fishermen will begin to start buying their own sets.

We are looking to secure further funding to continue scientific trials, collecting additional data on both prawn and Nephrops fisheries to make our results more robust. We also want to extend the project to the roundfish fisheries of the west coast of Sweden and the Baltic Sea. Until that funding is secured, members are free to borrow the trawl doors to try out in their fisheries, but if they do they won’t get any further compensation and the data won’t be collected in a scientific manner. In the meantime, we plan to upload our results onto the GearingUp website and hope they will prove useful for fisheries across the North Atlantic.

More from SLU on the selective gear projects:

https://www.slu.se/globalassets/ew/org/inst/aqua/externwebb/selektivt-fiske/aqua-reports-2018-13.pdf

More at SLU website on selective gear trials:

https://www.slu.se/institutioner/akvatiska-resurser/selektivt-fiske/