Ghost nets are commercial fishing nets which 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 main types of nets which become ghost nets are gill nets and drift nets which catch pelagic fish in mid-water or at the surface, while deep-sea trawl nets can also become ghost nets, these are much less damaging than the other types. Nets can be abandoned by commercial fishing vessels for the following reasons:
- Human error can mean that drift and gill nets that are not secured to marker buoys properly and work themselves free to become ghost nets.
- Bad weather can see drift and gill nets can be pushed by the tide and weather into rocks or reefs where they become snagged and need to be cut free.
- Nets can be lost by accident. For example a drift net which is set too high in the water could be cut in half by the propeller of a passing boat creating a ghost net.
- 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 than 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/marine animals may be killed each year by ghost nets. However, the book Commercial Fishing – The Wider Ecological Impacts (2000) by Moore and Jennings states that 7,000 kilometers of drift nets are lost each year in the north Pacific and a estimated 100,000 animals were killed in lost nets around the coast of Newfoundland between the years 1981-84. They also state that a 1.5 km drift net recovered from the coast of the Aleutian Islands in the Pacific Ocean/Bering Sea contained over three hundred dead sea birds. 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 which is either accidentally lost or intentionally dumped at sea amounts to 640,000 tons every year.
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 rot away quickly if they were ever lost at sea. However, from the early 1960s onwards synthetic material such as nylon, and monofilament have been used. Synthetic materials such as these are stronger, lighter, much more abrasion resistant and crucially do not biodegrade or rot naturally meaning that ghost nets which would have rotted away within weeks or months will now last for many years. Until the 1960s gill and drift net size was unregulated and nets of up to twenty-five miles long were common. Modern synthetic gill nets are also near-invisible once submerged, meaning that fish have much less chance of avoiding them. Furthermore, they do not become covered in marine vegetation in the same way that old nets do, meaning they remain difficult to spot for the entire time they are in the sea. However, the effectiveness of gill and drift net fishing, along with advent of synthetic materials saw limits imposed, with the EU and US authorities restricting net lengths to around 1.5 miles, meaning that at least 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 simply 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 again) 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 obviously also take place further reducing the number of fish in the net. Eventually 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 once the small fish, crabs and decomposition have done their work 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. However, a storm may 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, usually willow 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. However, unlike nets there is a simple solution to prevent or at least massively reduce the destructive potential of lost lobster crabs and pots – the ‘rot out panel’. The panel on one side of the pot is tied in place with cord or string made out of a biodegradable material such as cotton. This will secure the panel in place for a fishing session but if the pot is lost the cord will soon rot away in the seawater and the panel will fall away, allowing any crabs inside to escape. This obviously prevents ghost fishing from taking place and prevents crabs being killed unnecessarily. Most 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 fish with pots with a rot out panel in place.
Recreational anglers can also be responsible for forms of ghost fishing. Rigs which are lost due to snags still have a baited hook attached to them and fish will obviously take these baits and effectively become tethered to the seabed. There is little that can be done to stop this from happening. However, each hook can only catch a single fish meaning the number of fish killed in this way is a tiny fraction of the numbers 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 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. However, it is more common for divers to go down to a ghost net and bring it back to the surface using floats. 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 ghost fishing problem. The massive 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. A full-sized otter trawl net can cost many thousands of pounds and fishermen are therefore keen to retrieve lost nets from the sea rather than see them become ghost nets. Laws could be strengthened to required commercial fishing vessels to report lost nets and log the location at which the gear was lost. There could also be financial incentives for fishermen recovering old nets from the sea. Finally, biodegradable nets are also being developed, meaning that the nets would naturally disintegrate and break up after a set amount of time in the water. Furthermore, an Italian company called Aquafil is pioneering a new method which recycles recovered ghost nets into a synthetic material which can be used to create clothing. International swimming brand Speedo and American surfing band Outerknown have both used the material in their products.
None of these ideas will eliminate ghost nets completely, but they will help to reduce the problem.