Ghosting fishing nets

Ghost nets also known as "Abandoned, Lost or Discarded Fishing Gear" (ALDFG) or nets that are discarded in the sea are becoming to be known as one of an important problematics in the ocean. Still, after being discarded or lost, organisms still entangle into them. Some studies evaluated that there are more than 640.000 tonnes of such gear entering the seas every year. More than 2.5 % of fishing gear deployed is evaluated to be lost annualy in the sea.

When lost nets continue to fish autonomously, they catch high-value commercial species that die and rot uselessly on the seafloor. Studies estimate that ghost fishing reduces potential commercial fish catches globally by up to 5% annually, costing the international fishing industry billions in lost potential revenue.

Fishing nets in the bottom of the sea can be long as several hundreds of meters, and because of that many organisms can get entangeled into them. Since they can not escape, they can face dying because of entaglement. Discarded and forgotten fishing gear has been identified as one of main causes of seabed degradation and may cause mortality of many organisms.

Because modern commercial gear is made of highly durable synthetic plastics (like nylon, polyethylene, and polypropylene), it remains intact for up to 600 years. Lost nets keep catching fish; those fish die, attracting scavengers (turtles, sharks, crabs), which then get trapped themselves in a perpetual, deadly cycle.

Another negative impact is the degradation of plastic into smaller fragments of microplastic and by that a release of toxic chemical compounds into the ocean.

In the past, fishing gear was made from natural fibers, and after being lost or discarded, degraded in the ocean within several weeks. Later, syntetic fibers with longer duration came into use, and became the most used material for fishing nets.

Traditional synthetic nets take up to 600 years to decompose, during which lost gear continues to trap marine wildlife. Microplastic may enter the food web and later on, ends in human food.

To stop the problem at the source, extensive research is shifting commercial fishing from permanent plastics to Biodegradable Fishing Gear (BFG). Biodegradable nets offer a viable solution, though the transition involves a careful balance between environmental benefits and practical performance challenges. Nets made from such materials performe with the same strength and flexibility as standard nylon and if lost, they completely decompose into harmless biomass in two to three years, leaving zero microplastics behind.

The most common materials used to manufacture biodegradable fishing nets fall into two primary categories: synthetic biopolymers (which replicate the strength of plastic but break down in seawater) and natural plant-based fibers (traditional, highly sustainable choice).

Synthetic Biopolymers are engineered materials designed to behave exactly like nylon while in use, but rapidly degrade via marine microbes if lost at sea. While synthetic biopolymers dominate modern commercial fishing trials, natural fibers are seeing a massive resurgence for specific trap, net, and line applications. These include material from plants, such as hemp, sisal and coconut.

Discarded and forgotten fishing gear has been identified as one of main causes of seabed degradation and may cause mortality of many organisms.

Surveys made in the Adriatic Sea have shown high levels of discarded fishing gear, in some areas over 30 kg of discarded or forgotten fishing gear per square kilometer. In a study of discarded or lost fishing gear, presence of such objects were recorded on more than half of the reefs studied.

Also in aquaculture, farming of shellfish like mussels and oysters, as well as seaweed), plastic usage is incredibly intensive. In the aquaculture sector, the farming of shellfish—such as mussels and oysters—alongside seaweed cultivation has long been championed as a sustainable alternative to traditional finfish farming, yet it harbors a hidden and heavily plastic-intensive infrastructure. Nearly every stage of production relies on synthetic polymers, primarily due to their durability, low cost, and resistance to the harsh marine environment.

Ironically, because shellfish are highly efficient filter feeders, they ingest these tiny plastic particles, introducing them into the marine food web and potentially onto consumers' plates. Furthermore, the sheer volume of plastic gear used increases the risk of "ghost gear" accumulation when equipment breaks loose during storms, contributing significantly to global marine debris and creating long-term ecological hazards for ocean ecosystems.

Floating or submerged nets frequently wrap around the propellers, rudders, and intake valves of passing commercial cargo ships, cruise liners, and small fishing vessels. This causes catastrophic engine failure, costly dry-dock repairs, and dangerous strandings at sea for mariners.

A potential solution to the problem of discarded fishing gear is the implementation of various removal actions that can lead to the reestablishment of benthic communities. Marine conservation groups, local fishers, and specialized technical divers collaborate globally to tackle the ghost gear crisis through highly coordinated underwater recovery operations.

These actions begin with mapping the ocean floor using side-scan sonars and underwater drones to locate heavily entangled nets and traps. Once identified, expert dive teams descend to deep shipwrecks or fragile reefs, using specialized cutting tools to release live marine life before securing the heavy plastic structures to underwater lift bags.

When inflated, these bags safely float hundreds of kilograms of compacted gear to the surface, where recovery vessels haul it aboard. By pulling this lethal, centuries-enduring plastic out of the water and funneling it directly into specialized recycling facilities, these cleanup missions permanently break the destructive "ghost fishing" cycle, restore choked marine habitats, and breathe life back into vulnerable coastal ecosystems.

Major international research consortiums have developed and deployed specialized gear tracking systems. These are affordable, low-impact acoustic markers attached to nets that remain completely silent to avoid disturbing marine mammals, but emit a location signal when queried by a tracking device, allowing fishers or recovery divers to quickly pinpoint and retrieve gear if it breaks loose. Modern projects successfully combine high-resolution underwater sonar with autonomous robotic marine vehicles (drones). These drones use artificial intelligence processing algorithms to scan the seafloor, automatically mapping out and retrieving lost nets in heavily congested regions.

References:

- Angiollilo M. and Fortibuoni T. 2020. Impacts of Marine Litter on Mediterranean Reef Systems: From Shallow to Deep Waters. Frontiers in Marine Science 7: 581966.

- Consoli P., Sinopoli M., Deidunc A., Canese S., Bertie C., Andalorob F. and Romeo T. 2020. The impact of marine litter from fish aggregation devices on vulnerable marine benthic habitats of the central Mediterranean Sea. Marine Pollution Bulletin 152: 110928.

- Dąbrowska A., Łopata I. and Osial M. "The ghost nets phenomena from the chemical perspective" Pure and Applied Chemistry, vol. 93, no. 4, 2021, pp. 479-496. https://doi.org/10.1515/pac-2020-1102

- Gilman E., Chopin F., Suuronen P. and Kuemlangan B. 2016. Abandoned, lost and discarded gillnets and trammel nets: Methods to estimate ghost fishing mortality, and the status of regional monitoring and management. Rome, Food and Agriculture Organization.

- Moschino V., Riccato F., Fiorin R., Nesto N., Picone M., Boldrin A. and Da Ros L. 2019. Is derelict fishing gear impacting the biodiversity of the Northern Adriatic Sea? An answer from unique biogenic reefs. Science of the total Environment 663: 387-399.

- Pasanisi E., Galasso G., Panti C., Baini M., Galli M., Giani D., Limonta G., Tepsich P., Delaney E., Fosii M. C. and Pojana G. 2023. Monitoring the composition, sources and spatial distribution of seafloor litter in the Adriatic Sea (Mediterranean Sea) through Fishing for Litter initiatives. Environmental Science Research 30: 90858-90874.