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How fish farm nets are cleaned affects how much microplastic is released into the ocean
The fishing and aquaculture industries are major consumers of plastic. But research shows that simple methods can reduce emissions.
Rough seas and aggressive net cleaning can lead to more microplastics in the ocean.
Researchers have therefore been investigating how to reduce these emissions by choosing better materials and methods for cleaning fish farming nets.
“Microplastic emissions are the result of complex interactions between material choices, a rope’s usage history, and cleaning methods,” says Andy Booth, chief scientist at SINTEF Ocean.
He leads the research project. Tests from the project show that some recycled ropes and nylon nets – both coated and uncoated – seem to release more microplastics than other rope types.
Net cleaning method plays a role
Farming nets are often affected by fouling, which is the accumulation of unwanted materials such as microorganisms and algae. This means they need to be cleaned regularly.
Researchers therefore tested several cleaning methods.
Using a cleaning robot proved gentler than traditional net washing and cavitation washing – a water jet that forms tiny bubbles that implode. The tests showed that robot brushing caused less damage and more even wear on the coating.
“The nets are exposed to what we call mechanical stress that can cause them to shrink or wear. So cleaning them actually contributes to accelerating the release of microplastics,” says Booth.
He adds that microplastics are released as nets wear out and break down over time.
“Plastic not only contributes to environmental pollution, but it can also contaminate seafood products,” he says.
Nets are often coated with wax, resin, or acrylic-based products to protect against UV damage, support cleaning-in-place (CIP), and reduce wear and tear.
The researchers fond that used nets released more microplastics than new ones, especially in high-wear areas. These are typically just below the water surface and on the sea floor.
A good start and solid basis for a new standard
Collecting samples at sea cages has been challenging, but lab tests clearly show differences between nets made from different materials.
However, these tests do not fully reflect real environmental conditions or typical cleaning processes.
“When we tried to conduct field studies, the data basis became much less clear due to the complex test conditions,” says Booth.
Still, the emissions data and project reports provide a solid basis for developing a new industry standard.
Booth says that most of the tested solutions arlearly exist, so the aquaculture industry can use them now by applying the project's findings in how they buy and maintain equipment to reduce microplastic emissions
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