The invisible danger at sea

by Thomas Jensen
Nets made from synthetic plastics are extremely environmentally resistant and take 400–600 years to break down in water.

Ghost nets endanger wildlife and harm the environment

This article was featured in Eurofish Magazine 3 2021.

Every day, nets and other fishing gear are lost in the vastness of the oceans or are intentionally disposed of at sea. These ghost nets keep on catching, however, and can become deadly traps that threaten marine biodiversity. Even their gradual disintegration presents dangers, because it contributes to microplastics pollution in the seas. There is still no practical solution in sight for this issue.

A few decades ago, fishing nets were still mainly made from perishable natural fibres such as cotton yarn, hemp, manila or sisal. These were regularly impregnated with preservatives at a huge expense to prevent their disintegration. It was therefore seen as great progress when the first nets made from synthetic, almost completely rot-proof plastics such as polypropylene, polyethylene and nylon (polyamide) arrived on the market. The environmental cost of this supposed progress was willingly accepted at the time. Synthetic polymer net materials take an average of 400 to 600 years to completely break down in nature. Lost fishing gear can therefore remain capable of catching marine life and endanger wildlife for decades. Just like our packaging waste, it also contributes to plastic pollution of the seas.

No responsible fisher would leave their expensive fishing gear in the sea intentionally. But the loss of nets cannot be completely prevented in the fishing industry, because the material ages, and can end up lost in the sea due to tearing, accidents and other adverse circumstances. However, where there are no options for disposal or they are costly, nets are also carelessly thrown into the sea. After all, the sea is vast and the nights are dark. There is a terminological distinction made between “End-of-Life Fishing Gear” (EOL) and “Abandoned, Lost and Discarded Fishing Gear” (ALDFG) when it comes to ghost nets. This kind of pollution of the seas is forbidden by law almost everywhere. European fishers are obligated to retrieve lost nets or report losses to the supervisory authorities. In this case the responsibility for their retrieval lies with the state. This, at least, is what is stated in the EU fisheries control regulation. However, no Member State is compulsorily obligated to retrieve lost nets. Often, the political will and also the financial means to retrieve lost nets are lacking. Potential risks to the ecosystem and environmental damage clearly do not justify any particular urgency in this case. Often only the waste that endangers the safety of shipping routes is cleared up.

The extent of the ­problem is often unknown

Storms and accidents at sea are among the most common causes for fishing gear being lost as ghost nets. Gillnets are torn from their anchors and carried away by the current. Marker buoys for nets and crab pots can be lost, which makes finding fishing gear more difficult. Trawl nets can get stuck on rocks, corals, wrecks or other obstacles on the sea floor. Dolly ropes are woven into the underside of many bottom trawl nets to protect against abrasion caused by sharp rocks and banks of mussels, and can be torn off. Fishing gear is frequently lost overboard during shipping accidents. Unfortunately, in many regions it is still standard practice to dispose of worn out or overly damaged nets in the sea, because bringing them back to land would result in unnecessary costs. Net dumping is also a common practice in IUU fishing. If illegal fishers are at risk of being detected during their nefarious activities, they often cut the lines and throw the nets overboard to hide potential evidence of their misdeeds.
In 2009, the UNEP and FAO estimated that at least 640,000 tonnes of nets and other fishing gear is lost, abandoned or thrown away at sea each year. At that time this constituted some ten percent of the waste ending up in the oceans globally. Today these quantities could be even higher, but might potentially be lower due to increased environmental awareness. It is difficult to say precisely what quantity of net materials ends up in the seas each year. All figures quoted in the media and public forums regarding this are only estimates, which may be totally exaggerated or underestimated due to vested interests. How frequently this takes place, if the figures cannot be correctly verified, is the subject of lively speculation. In this exaggeration competition, it is difficult to identify those few studies that at least attempt objective quantification. In the year 2020, the WWF claimed that at least one third of the plastic waste in the sea globally is composed of fishing gear such as nets and ropes. It also claimed that some 500,000 to one million tonnes would be added each year. A report from World Animal Protection (WAP) estimates that at least 700,000 tonnes of fishing gear from commercial fisheries is disposed of in the sea each year. EcoWatch uses the 640,000 tonnes figure from the FAO, but for ResearchGate this is too low, it assumes that 6.4 million tonnes of fishing gear ends up in the oceans each year.

Diverse threats to ­wildlife at sea and on land

According to Greenpeace, six percent of all nets used, nine percent of fish traps and crab pots and 29 percent of all longlines end up in the ocean as marine waste. Pham et al. (2014) estimate that approximately one third of the plastic waste on the sea floor of the North Sea, the Atlantic, the Arctic and the Mediterranean is composed of fishing gear, mainly nets and ropes. And the environmental project Ocean Cleanup, founded by the Dutchman Boyan Slat, claims to have determined that fishing nets and net components, ropes and fishing lines make up almost half of the enormous 1.6 million square kilometre Great Pacific Garbage Patch. Approximately 46 percent of the 79,000 tonnes of plastic waste in this area between the US West Coast and Hawaii, which is some three times the size of France, is said to be made up of lost or thrown away fishing gear.

These are all only vague estimates, but regardless of their credibility, it cannot be disputed that ghost nets represent a serious problem that urgently requires a solution. This is because durable fishing gear continues to fulfil its original purpose as ghost nets: fish and numerous other animals get caught in the mesh. Fish remain caught in the nets and unwillingly become bait that attracts larger marine animals such as porpoises, seals, dolphins, diving birds and sea turtles. They can also become entangled in the nets and get injured or stuck and drown. Sometimes animals mistake floating bits of nets for food and perish miserably as a result. World Animal Protection estimates that more than 136,000 seals, sea lions and great whales lose their lives to ghost nets each year. An unknown number of seabirds, turtles, fish and other species meet the same fate. The Internet platform claims that the number of animals lost to ghost nets is significantly higher, at “up to 650,000 marine animals”. A scientific study (Kühn et al. 2015) lists 344 species that have already been found in ghost nets. Almost half of these (161 species) were seabirds, marine mammals or aquatic turtles. Other estimates arrive at approximately 800 species. Depending on the source, the losses to commercial fish stocks due to stray ghost nets run between 5 and 30 percent. But again, these are only assumptions and claims that cannot be veri
fied and therefore also cannot be disproved.

Microplastics can enter the food chain

Nobody would seriously dispute that ghost nets cause damage to marine wildlife. However, damage to the ecosystem also occurs through mechanical effects such as when nets cover reefs and suffocate them or fish baskets get caught on corals. Even nets that are washed ashore can have destructive effects, because seabirds like to use the soft material to build their nests. The tear-resistant loops of the nets can have deadly consequences for old and young birds if they get stuck in them.


Ghost nets that permanently remain at sea gradually become brittle and over the decades slowly crumble into ever smaller particles until they become microplastics measuring less than 5 millimetres. This does not in any way solve the problem of ghost nets, however, but rather gives it an extra dimension, because the tiny plastic particles continue to drift through the sea, releasing chemicals such as plasticisers and flame retardants, and can enter the marine food chain. An analysis of the stomach contents of some species of fish from the North-East Atlantic found that 73 percent of the animals studied had microplastics in their digestive tract (Wieczorek et al. 2018). 98 percent of these plastic particles were fibres for which the origin – ghost nets or other plastic waste – could not be identified, however the study underlined the urgency of solving the plastics problem in general and that of ghost nets in particular.

Retrieval of ghost nets is difficult and expensive

But how does one combat a problem of global dimensions that is not visible to most people, and the solution for which involves a lot of effort and is also expensive? Locating and retrieving ghost nets from the oceans requires enormous efforts. Even in shallow coastal waters, professional divers and technical equipment are often needed, the costs of which can quickly reach several thousand euro per day at sea. This is often more than the cost of new fishing gear, which explains why many fishers would rather invest in new gear than retrieve lost equipment. In deeper regions of the sea beyond continental shelf areas, attempts at retrieval are unlikely to be successful in any case. Although net losses at sea can never be completely prevented, some causes for it can be (or can be limited). For example, illegal disposal of worn-out nets in the sea could be alleviated if the regulatory authorities introduced personal registration of all nets and made handing in old nets easier. Setting up a deposit and return system for nets would also be a sensible idea. Responsibilities would have to be clarified and tasks clearly allocated.

The legal foundations are actually already in place. At an international level, both the UN Convention on the Law of the Sea and the MARPOL Convention prohibit the disposal of fishing gear at sea. Article 48 of the EU Fisheries Control regulation obliges fishers to report the last known location of lost nets. However, such requirements are often ineffective, because they are not sufficiently enforced. Various national and international organisations, as well as private companies, attempt to fill the gap by increasing awareness of the problem and publicising retrieval of ghost nets from the seas. These include, for example, the WWF, the Ocean Voyages Institute, Gesellschaft zur Rettung der Delphine (Dolphin Rescue Society), Nofir, Healthy Seas with Ghost Diving and other initiatives. The Global Ghost Gear Initiative (GGGI), which was established in 2015 by World Animal Protection, specifically deals with the issue. It involves NGOs, the private sector, the fishing industry, scientists, governments and top-level organisations (e.g. UNEP, FAO, NOAA, CSIRO, EU-GD, MARE) working together on specific projects. As part of a project to identify fishing gear in Pacific waters, for example, the GGGI is working together with local fishers, the FAO and the state authorities of Indonesia and the Netherlands.

Lots of ideas, but no ­general solution in sight

There are plenty of ideas, technical solutions and other measures globally to prevent the loss of fishing gear or to make finding and retrieving it easier. These include tiny acoustic underwater transponders that can be attached to the nets and require very little electricity, so that they can work for months without requiring new batteries. With new GPS locating systems, it would be possible to precisely mark the locations at which nets were lost. To keep electrosensitive sharks away from ghost nets, it is often enough to simply attach small magnets to the net. Side-scan sonars, which generate 360-degree maps of the sea floor using sound waves, are helpful for tracking down lost fishing gear. With their help, sources of interference such as ghost nets and other fishing gear can be detected. Underwater drones can also be helpful, such as the remotely operated vehicles (ROVs) from Deep Trekker.

Some projects focus on prevention and offer fishers financial incentives for reporting lost gear or old damaged nets, so that they never become ghost nets in the first place. Perhaps net materials that degrade much more quickly in the water and thereby limit the lifespan of ghost nets could also be used. This option has already been in use for a long time for lobster pots on the North American coast. They have escape windows that dissolve in the water after a certain time, so that crabs caught in them can escape from the traps through these “emergency exits”. Where retrieval of ghost nets with divers is too expensive, too dangerous, or not possible for other reasons, net rakes are frequently used. The nets are caught on their prongs and can then be hauled up. There are even smartphone apps that have been developed recently, with which practically anyone can report a find of stray fishing gear. Using this notification system, important information such as the location coordinates, immersion depth and a brief description of the objects found – photos can even be uploaded – are recorded in a database. Depending on the level of threat, professional divers can then take care of retrieval.

Recycled ocean plastic is often only good for advertising

Despite high engagement levels, many retrieval actions by environmental organisations and activists have little more than symbolic significance. Their real value lies in the broad reach they have with the public, which increases awareness of the problem. It can be difficult not to exaggerate the significance of individual actions in order to boost donations for a good cause. But what actually happens to ghost nets after they are retrieved? Disposal methods vary depending on region and range from bringing nets to landfills to utilisation for energy in waste incinerators to material recycling, which is however only rarely undertaken as the required logistics are lacking. A few years ago, however, a GGGI project in Alaska attempted to develop reasonable options for recycling old and ghost nets.

The recycling of ghost nets from the sea is expensive and requires a lot of effort, which often makes it uneconomical. Gillnets are usually weighted at the bottom with poisonous lead that must be removed before recycling. The nets are also contaminated with sand, sludge and organic materials such as algae, barnacles and fish remnants. Another difficulty is that the nets are often made up of a mix of different plastics, which takes a lot of effort to separate. In principle, thin monofilament nylon gillnets can be spun into yarn and thicker trawl nets and cables melted down into pellets, but this is usually not done in practice due to the high cost. This makes it all the more astonishing that the quantity of products that claim to be made from “recycled ocean plastic” is steadily increasing. The “ocean plastic” advertising promise often turns out to be a misleading marketing trick that plays with the expectations of many customers but really only serves to swell sales. Ma
ny of these swimming shorts, sports clothes, mobile phone cases, sunglasses and skateboards, rucksacks and carpet tiles that claim to be “helping the marine environment” are actually made of recycled plastic of which only a small percentage or none at all comes from the sea.


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