This study investigates the feasibility of material recycling for retrieved gillnets from the Baltic Sea collected during a campaign of the World Wildlife Fund (WWF) Germany. Fragments from the material were analysed by Fourier transform infrared (FTIR) spectroscopy revealing polyamide 6 (PA6), polypropylene (PP) and polyethylene terephthalate (PET) in net material, swim lines and sink lines, respectively. A visual examination by microscope found large quantities of minerals attached to the surface of the material as well as in knots and loops of the polymer structure. Ash tests showed that a pre-treatment of the material including sorting, shredding, density separation and washing allows to reduce the mineral content from more than 45% of the total to 1.1%. However, for a separation by density, it is important that the entangled fibres can move freely. This is a major challenge for a primary or secondary mechanical recycling because a substantial fibre length reduction is required for the small polymer fibres down to a diameter of 20 µm. Another challenge for all kinds of recycling is the presence of lead lines in gillnets. Automated technology for removing these does not exist until now. A manual removal is indispensable to limit the level of contamination. Due to the complex pre-treatment and the elevated heavy metal concentrations also a tertiary or feedstock recycling seems not to be a possible pathway for retrieved gillnets. Yet, other options such as a primary recycling in concrete or bitumen additives or quaternary recycling via incineration may be conceivable alternatives. But there are also some arguments against these options. Better product design must be the goal to prevent plastic pollution and establish a functioning circular economy. In this context, the heavy metal contamination by abandoned, lost or otherwise discarded fishing gear (ALDFG) must be stopped.
In this pilot project, World Wild Fund for Nature (WWF) Germany works together with regional divers, fisherfolk and public authorities to reduce the impact of lost fishing gear in the Baltic Sea. If not removed, ghost gear poses a threat to the marine environment and wildlife including seabirds, seals, harbour porpoises and fish. Over decades to centuries, lost fishing nets and ropes shed microplastic fibres into the marine environment. Removing this hazard reduces both the risk of entanglement as well as the contamination of the marine foodweb through ingestion of microplastics and associated chemicals. Identifying lost fishing gear in the marine environment poses one of the largest challenges impeding mitigation through gear retrieval operations. Lost gear can be drifting on the surface, in the water column, or can be sunken to the seafloor as a result of material composition, fouling, and entanglement. In the Baltic Sea, ghost gear is located on the seafloor and not visible during visual surface surveys from vessels. Identifying an efficient search methodology was therefore a key aspect of WWF’s ghost gear project. After trials with different search and retrieval methodologies, WWF Germany found sonar search technology to be the most efficient technique to locate lost gear on the seafloor. Sound waves avoid the limitations faced by divers or visual cameras in low-visibility environments, and a substantially larger area can be covered. In contrast to diving teams focussing on wreck retrievals, the many nets lost on the seafloor remain unnoticed by divers under most circumstances. A combination of sonar search providing exact GPS positions of suspect ghost gear, diver verification through the WWF Ghostdiver App, point-on retrievals with fishing vessels, and manual sorting for waste management provides an efficient methodology for long-term political implementation of regular lost gear retrieval campaigns.
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