Ghost nets are commercial fishing nets that have been lost or abandoned by a fishing vessel and remain in the sea, continuing to catch and kill fish and other forms of marine life. The most damaging types of ghost nets are abandoned gill and drift nets which catch pelagic fish in mid-water or at the surface, although deep-sea trawl nets can also become ghost nets. Nets can be abandoned by commercial fishing for a number of reasons. Nets can be lost due to human error, such as drift and gill nets that are not secured to marker buoys properly and work themselves free to become ghost nets, while nets can also be lost overboard in bad sea conditions or in exceptional circumstances, a coming storm or unexpected bad weather may see fishermen abandon their nets and head back to port without delay. Fishermen may then struggle to find their nets when they come back out to sea, especially if they are in a non-GPS equipped vessel.
The Scale of the Problem
Due to the unreported nature of ghost nets, it is very difficult to come to any conclusions about how many ghost nets there are in the world’s seas and oceans, or calculate how many fish and marine animals may be killed each year by ghost nets. The book Commercial Fishing – The Wider Ecological Impacts (2000) by Moore and Jennings states that 7,000 kilometres of drift nets are lost each year in the North Pacific alone, and estimated that 100,000 animals were killed in lost nets around the coast of Newfoundland between the years 1981 – 84. The tenth edition of Introduction to the Biology of Marine Life which was published in 2010 underlines the problem of lost fishing gear, stating that the total amount of fishing gear that is either accidentally lost or intentionally dumped at sea amounts to 640,000 tons every year. In 2018 a ghost fishing net in the Caribbean made international news. Discovered by British fisherman and diver Dominick Martin-Mayes the net was 40ft by 40ft and contained trapped sharks, fish and other marine life. Martin-Mayes estimated that the net had drifted for more than one hundred miles through the sea. A spokesperson from the nearby Cayman Islands government said that they were tracking the movement of the net and would either tow it to an area where it would not cause further harm or remove it from the sea entirely. Ghost nets are certainly a problem that affects the UK. In January 2019 a thirty metre long (100ft) lost or abandoned new was recovered off the coast of Cornwall. Fifteen people were needed to pull the net from the sea and a tractor was eventually used to remove the net from the beach. A local charity took the new away to be broken up and recycled.
Modern Net Materials and Technology
Advances in modern technology have made ghost nets a much more serious problem. Until the middle of the twentieth century most commercial fishing nets were made with natural fibres. These nets would biodegrade relatively quickly if they were ever lost at sea. However, from the early 1960s onwards synthetic materials such as nylon, and monofilament have been used. These materials are stronger, lighter, much more abrasion resistant and crucially do not naturally biodegrade meaning that ghost nets that would have rotted away within months will now last for many years. Modern synthetic gill nets are also near-invisible once submerged, meaning that fish have much less chance of avoiding them.
Until the 1960s the size of gill and drift nets was unregulated, meaning that nets over twenty miles long were used. The effectiveness of gill and drift net fishing, along with the advent of synthetic materials meant that limits and regulations on nets were imposed, with the United Nations restricting net lengths in international waters to around 1.5 miles, meaning that super-sized twenty mile-long nets are no longer used and can no longer become ghost nets.
Ghost Nets ‘Cycle of Destruction’
When lost or abandoned at sea gill and drift nets continue catching fish. With the durable nature of modern fishing nets this can continue for a very long time. It can often take many months, or even years, and several storms or other spells of bad weather to break up a net to the extent that it no longer threatens sea life. Due to the series of weights and floats which are used to set gill nets they can sometimes become stuck in a cycle of sinking to the seabed and then returning to the surface which is described below.
The ‘Cycle of Destruction’: The animation above shows a gill net becoming disconnected from a fishing vessel. Although the net becomes damaged (and loses its flags and marker buoys making it harder to find) it continues to catch fish. Eventually, the net catches so many fish that the floats can no longer hold it at the surface and it sinks to the bottom of the sea. Once here small fish (which are too little to become caught in the mesh) begin to eat the fish caught in the net, as do crabs and other crustaceans. Natural decomposition will also take place further reducing the amount of fish held in the net. Over time all of these factors will have the effect of reducing the weight of fish in the net to the extent that the floats will be able to carry the net back to the surface. Here it will continue fishing until it becomes heavy with captured fish and yet again sinks back down to the seabed. The process will be repeated and the net will yet again continue to the surface and begin to catch fish again. Although the animation above only shows this happening twice the truth is that modern nets are so well made and durable that this process can happen many times before the net becomes too worn and damaged to catch fish. Indeed, it may require a storm or period of prolonged bad weather to cause the net to become tangled up and no longer pose a threat to fish.
As well as catching fish ghost nets are also responsible for the deaths of other forms of marine life such as turtles, dolphins seals and sharks, many of which are killed throughout the world by ghost nets. Recreational divers can also be threatened by ghost nets. In 1998 42-year-old Megan Reehling became tangled in a ghost net while in the sea at Puget Sound near Seattle, USA. She was equipped with a knife and made an attempt to cut through the net but ran out of air before she was able to free herself.
Other Forms of Ghost Fishing
Traditional crab and lobster pots used to be made out of wood and rope. However, these have been replaced by much stronger and durable modern plastic and metal designs. Just like ghost nets, lobster and crab pots will continue to catch once they have been lost or abandoned, but unlike nets, there is a simple solution to prevent or at least significantly reduce the destructive potential of lost lobster crabs and pots – the ‘rot out panel’. This is a panel on the side of the pot which is tied in place with cord or string, while in some cases the panel itself is made out of a biodegradable plant-based material. This will secure the panel in place while it is used for fishing but if the pot is lost the cord (or the panel itself) will begin to biodegrade and will eventually fall away, allowing any crabs or lobsters inside to escape. Many crab pots sold around the world are fitted with some form of rot out panel and in some parts of the world it is a legal requirement to use crab and lobster pots which are fitted with a rot out panel.
Recreational anglers can also be responsible for forms of ghost fishing. Rigs that are lost due to snags still have a baited hook attached to them can continue to catch fish – a problem which has no easy solution. Anglers can minimise this by using rigs that have a weak link release so the majority of the rig can be retrieved if the weight becomes snagged and using other methods and techniques to reduce snags. It also has to be noted that each hook on a lost rig can only catch a single fish meaning the number of fish killed in this way is a tiny fraction of the number of fish caught by the ghost nets left by commercial vessels.
Problems and Solutions
One of the major problems with ghost nets is that no one wants to take responsibility for them or spend time, money and resources recovering them from the sea. Trawlers can re-trawl the area where a net has been lost using a grappling hook to recover the net but the smaller scale and less well equipped inshore fishermen using gill or drift nets are likely to write off a lost net with little to no attempt to recover it and simply leave it unreported.
Even if ghost nets can be found then recovering them from the sea is an expensive, dangerous and time-consuming operation, with only a small number of specialised charities and ocean conservation organisations having the resources to locate and recover ghost nets. Due to the danger of becoming tangled in the nets both British and American authorities state that ghost nets should only be removed by fully trained and professional divers and volunteers should not attempt to remove ghost nets.
There are a number of solutions put forward to the problem of ghost fishing nets. The advances that have been made in recent years with GPS technology and 3D seabed imaging have allowed commercial fishermen to avoid snags and structures which will see them lose gear, and can also be used to mark the point where fishing nets have been lost. The company NetTag which is a collaboration between British, Spanish and Portuguese universities along with leaders from Europe’s fishing industry are developing transponders that can be fitted to nets. These transponders are relatively cheap at €300 each, significantly less than the cost of a net. There is hope that they could be taken up throughout Europe’s fishing industry. However, it may be necessary to implement laws to compel fishermen to recover lost nets, as many fishermen may simply leave lost nets at the bottom of the sea as it is not economical to lose hours of fishing time to recover a net. Finally, biodegradable nets are also being developed, meaning that the nets would naturally disintegrate and break up after a certain amount of time in the water. While all of these new developments will help, the issue of ghost nets, and how to reduce their impact on the marine environment, is one which will continue for many years to come.