New ideas to reduce ghost nets in the sea
This article was featured in Eurofish Magazine 1 2023.
Only around 9 percent of the plastic produced worldwide is recycled. The vast majority is incinerated, ends up in landfill or in the sea and permanently pollutes the environment. It takes centuries before it breaks down into microplastics. Plastic waste in the oceans is a pressing problem that the fishing industry and aquaculture are also contributing to. Could nets and lines made from biodegradable plastics perhaps be a solution?
Synthetic organic polymers, usually referred to as “plastic” for simplification purposes, are today the most widely used man-made artificial material across the globe. Plastic can be produced in a wide variety of forms and used in different ways. From water bottles and disposable medical supplies to food packaging, clothing and lots more. The inert, durable and almost non-toxic material was seen as a good choice for many applications for a long time. Plastic has become ever-present, if not indispensable, in our convenience-based lives. More than nine billion tonnes of plastic have been produced worldwide since the 1950s. There were hardly any concerns about releasing plastic into the environment at that time. However, since then concern over environmental pollution caused by plastic has been growing. After all, every person disposes of an average of 52 kg of plastic waste per year. Much of this ends up in the sea, and plastic pollution there is now seen as a significant global environmental problem. Given the size of the problem, the attempts by some states to stem the growing tide seem to be almost in vain. The problem will not be solved by banning single-use cutlery and plastic cups. Plastic is not being successfully recycled everywhere by a long stretch. Even the International Convention for the Prevention of Pollution from Ships (1978 version) did not appreciably reduce the pollution burden on the oceans, if at all.
However, marine pollution is seen as a major and urgent problem by consumers worldwide. In a survey of more than 20,000 consumers carried out by GlobeScan on behalf of the Marine Stewardship Council (MSC), two-thirds of participants said that they were particularly concerned about the pollution of the seas. Vigorous countermeasures are urgently required, and above all preventative action, since once plastic has reached the ocean, it cannot be removed again, or can only be removed with a great deal of effort. Each potential contributor of plastic waste must make their own contribution towards keeping the seas clean. This includes the fishing industry and aquaculture, which are among the biggest polluters. According to estimates from the conservation organisation WWF, lost fishing nets account for one tenth of global marine waste. Apparently, approximately 640,000 tonnes of fishing gear is lost in the oceans each year, or is “cost-effectively” disposed of there. However, the term “cost-effective” is not accurate, since the environmental, social and economic follow-up costs of abandoned, lost or discarded (ALDFG for short) fishing gear made from synthetic fibres and plastics, which often remain in the oceans for centuries as ghost nets, are significant. They damage aquatic habitats and kill fish, marine mammals and sea birds that get caught in the net mesh. And even if the fishing gear then eventually breaks down into tiny particles and becomes pulverised into microplastics, these remain a permanent hazard, as they can enter marine food chains and harm marine animals.
Plastic can be found in almost all fishing gear
Fishing gear such as nets, fish traps, lines or lures made from polypropylene, high-density polyethylene or nylon has even been found at the edge of the Arctic and in deep-sea trenches, and is said to make up approximately 46% of the Great Pacific Garbage Patch. None of these types of plastic is naturally biodegradable and therefore they also do not return to natural materials cycles. The question therefore almost inevitably arises: why not turn to biodegradable plastics to manufacture fishing gear with a limited lifespan that can break down by itself after a certain amount of time? Even if this took two or three years, this would be a lot better than current plastic materials that last for 500 or 600 years. There are already plenty of existing models for this, such as compostable bags or packaging nets made from bio-based fibres that are manufactured from potatoes, sugar cane and other renewable resources. Most have similarly good properties to synthetic plastic, are break-proof, can be mechanically filled and have high seal strengths.
Bioplastics are not a cure-all for the plastic problem, but they are at least less environmentally damaging than conventional materials. Manufacturing them uses up hardly any fossil-fuel resources and has a reduced CO2 footprint. They break down more quickly in the wild and are less toxic. For example, they do not contain any bisphenol A (BPA), which is present in many standard plastics and can disrupt the hormonal balance of humans and animals. Fishing gear made from biodegradable material would also meet the United Nations SDG Goal 14.1 for sustainable development at an economic, social and environmental level that aims to prevent marine pollution of all kinds. It would also contribute towards SDG Goals 12.3 and 12.5, which call for the reduction of food losses along production and supply chains (ghost fishing causes fish losses in the production chain) by 2030.
But what are bioplastics and what does “biodegradable” mean? In principle, every plastic ages and degrades, including standard materials. However, these only break down into tiny particles or powder (microplastics) which do not return to the natural cycle. Biodegradable plastics such as products made from polylactic acid (PLA), which are mainly manufactured from sugars in maize starch, manioc or sugar cane, can in contrast be completely broken down by microorganisms into water, carbon dioxide and compost under the right conditions. According to the current definition, biodegradable means that the plastic must be 90% broken down within 12 weeks at a temperature of 60 degrees. This is relatively fast, but it does always take significantly longer than for normal organic waste that is produced in the household or garden. Shopping bags or yoghurt containers made from PLA, for example, take about three months to break down, while organic waste only takes two to three weeks. This is why biodegradable plastic cannot also be disposed of in the compost bin, because it would disrupt the technological processes in composting facilities due to its longer decomposition period.
Plastic in fishing gear must meet demanding requirements
What makes the search for biodegradable alternatives for the fishing industry and aquaculture exceptionally difficult however, are the extremely demanding requirements in both sectors. In contrast to traditional nylon nets, biomaterials seldom have the required tensile strength and the necessary mechanical performance features. Their relatively rapid decomposition following a net loss is an advantage, but it can increase the susceptibility of the fishing gear to breaks and thus increase loss rates. If the necessary certainty is lacking that the caught fish can actually also be hauled on board, because the net becomes increasingly fragile with age, it will likely be difficult to inspire enthusiasm for the new materials in potential users. All the more so as biodegradable nets are more expensive than traditional gear and need to be replaced more often due to their limited durability. There is also the issue that replacing the synthetic nets alone is not enough. This is because other equipment made from plastic is used in fishing that can be lost and then take centuries to break down into microplastics, which are potentially even more environmentally damaging than the original equipment. This includes anchor cables and lines, fishing lines, floats and artificial lures, to name just a few.
There still does not seem to be any ultimate solution to this global problem, but there have already been numerous initiatives such as the idea of biodegradable net materials. In Europe, politicians are taking a two-pronged approach to conserving and cleaning up the seas. Conventional plastic nets that are lost are to be retrieved to a greater extent, and the recycling of old nets in ports is to be improved. In addition to this, large-scale studies are attempting to discover whether conventional nets can be replaced by biodegradable materials. The requirements for biodegradable nets are demanding, as they must be similar to current fishing gear with regard to durability, handling, efficiency and cost. For example, as part of the E-REDES project in the Northern Littoral Natural Park (Portugal), gillnets made from biodegradable monofilament yarn that can be broken down by microorganisms after two years in sea water were tested under practical conditions. The experimental yarn has a similar breaking resistance to standard nylon monofilament, but is somewhat stiffer, which makes handling it more difficult for fishers.
Practically oriented studies are delivering promising results
The four-year, 4.2 million euro Innovative Fishing Gear for Oceans (INdIGO) project of the European Union’s Interreg programme, which is ending in June 2023, aims to develop the first completely biodegradable net with a controlled lifespan. Within two years, it should break down organically into natural materials, instead of microplastics. INdIGO also intends to show the way towards a suitable strategy for improving the recycling of worn-out fishing gear. The researchers involved have developed a mobile app that makes it easier to locate lost fishing gear. This important project is contributing to reducing the plastic waste in the Channel region between Great Britain and France by 3% by 2030. The INdIGO project also includes a survey of fishers that was carried out between December 2020 and August 2021. This showed that three quarters (73%) of respondents would consider using biodegradable fishing nets if the material and gear was similarly robust, solid and efficient as standard nets. Environmental arguments therefore also convince fishers and encourage them to convert to biodegradable fishing gear. However, because biodegradable nets are significantly more expensive – currently higher costs of around 10% are assumed, which are incurred more often due to the shorter usage duration of the nets – the changeover of course also depends on the financial framework conditions. This presents the question of whether consumers and politicians are really prepared to shoulder these additional costs. For example, through higher retail prices or corresponding subsidies.
The introduction of a voluntary sustainability standard (VSS) for biodegradable fishing has been considered as a possible solution to this problem. Similar standards are sometimes used already for coffee and cotton. Such a certificate could increase consumer awareness regarding the efforts of fishers towards sustainability and protecting ecosystems, which would hopefully provide them with improved market access and higher income.
In Mutriku in northern Spain, scientists from the AZTI research centre are working on replacing plastics used in aquaculture with more environmentally friendly materials as part of the European BIOGEARS project. This particularly relates to mussels, which grow on long cables in suspended cultures and are protected from predators by outer net walls. The cables and nets are made of plastic, which becomes a problem as soon as their useful life has come to an end. In the BIOGEARS project, the researchers involved are working on converting production to biodegradable plastics. Cables and nets made from natural materials that come from renewable biomass, such as from plant-based sugars, are being tested. The results to date have been encouraging, as tests with various different material recipes have resulted in promising approaches for further development. Net weavers and cable manufacturers, whose machines are really designed for processing standard plastic granulate, have in many cases given the green light. Conversion to compostable material was possible with only minimal adjustments.
Interest in bioplastics is increasing globally
The EU OCEANETS project is not just about biodegradable nets, this initiative is also about preventing, retrieving and recycling plastic waste in the oceans. It is well-known that sometimes parts of nets, or even entire nets, are lost on fishing trips by fishing vessels in rough seas or on sharp rocks. This is why the researchers in this EU project have developed a Web-based tool with which fishers can report the location and time of the event following such a loss. This means that other fishers are informed almost in real time of the risk of net losses in this area and can avoid the location. Moreover, OCEANETS aims to advance the development of new chemical and mechanical technologies for recycling old nets. Currently, a technology where the nets are cut into tiny bits and then melted down is favoured. This process, called compounding, produces a granulate from which synthetic yarn for functional and sports clothing can then be manufactured.
But work is being done on reducing net waste made from plastic in the seas in other locations across the world as well, not just in Europe. In South Korea, for example, where researchers from the National Institute of Fisheries Science in cooperation with the FAO already introduced biodegradable nets in 2016. The net yarn used, a polymer monofilament made from 82% polybutylene succinate (PBS) and 18% polybutylene adipate terephthalate (PBAT), has been shown to have similar durability to nylon in trawl net trials. Following its normal useful life, it is broken down by microorganisms in sea water in only two years, which significantly reduces the potential risk of ghost fishing. The new bionet was just as good at catching as standard nylon nets, which means it is very much financially worthwhile to use it, and its acceptance among fishers is gradually improving. Many still reject such nets, because biodegradable nets break and can be lost more easily than previous fishing gear and also cost more. Despite their many advantages, bioplastics are certainly not a cure-all or a magic bullet for combating net waste in seas and preventing ghost fishing. However, they can ameliorate the problem, particularly since new approaches to solving these problems are on the way.
Bioplastics with integrated predetermined breaking points
Recently, a plastic has been developed that is as stable as nylon, but breaks down when exposed to UV radiation for an extended period. Intense sunlight causes numerous breaks in the polymer chains (photolysis), causing the plastic to quickly crumble. It is made from isotactic polypropylene oxide (iPPO), which has been around since 1949. Changing the chain length and alignment of its basic elements made this polymer so mechanically stable that it meets the requirements of the fishing industry, for example, for ropes or fishing nets. In laboratory tests, the polymer chains of the plastic degraded to a quarter of their original length within just 30 days. If researchers succeed in pushing development to the point where the material degrades almost without a trace under UV light, this could be an important contribution to reducing plastic waste in the sea.
There is therefore some way to go before current nets can be replaced by biomaterials. Among other things, we must better understand what factors influence decomposition in the sea in order to be able to take a more targeted approach. Then perhaps the design of the polymers can even be tailored to specific requirements, so that the nets can be used effectively by fishers for a certain amount of time and, following a potential loss, can completely break down into harmless substances without residues and in an environmentally-friendly
way.
Manfred Klinkhardt