Fishing is well known in modern day society to be a destructive force impacting  the marine environment, however when thinking about the effects of fishing, most minds are drawn to those caused by live, active fishing gear, not the effects by those lost to the deep blue. It turns out that these man-made apex predators continue their path of destruction, even when disconnected from boats and moorings as a result of bad weather or impact from other fishing gear. Lost fishing gear partakes in what is known as ‘ghost fishing, continuing to fish and cause mortality of marine organisms long after they depart from the commercial fishing industry. There is no limit to the type of gear that can ghost fish; it has been observed to occur in gill nets, trammel netsseine nets, as well as crab pots and long lines. Nor is there a limit to the distance a ghost net can travel whilst fishing; nets washed up on the coast of Cornwall UK, have travelled nearly 3,000 miles from the coast of Maine, USA. The below video gives an insight into the diversity of organisms impacted by ghost fishing in the Indian Ocean, with special focus on the Olive Ridley sea turtle.

Level of Impact:

Seal entangled in ghost fishing gear gets released by help over divers
Picture of divers rescuing a seal from entanglement in a ghost fishing net. Photo credit: NOAA

Ghost fishing is a cause for concern as in 2007, just under 8,000 nets were lost in Europe alone, the equivalent of 209 km worth of net. A study estimated that ghost fishing in the Baltic sea caught up to 900 tonnes of cod over a 28-month period, the equivalent to 3.2%  of the total landings for that region during that time period. Another study found that discarded nets of the Greenland halibut fishery remained fishing for up to 8 years after loss. Although certain gear will have been designed to catch specific species, unlike live fisheries, ghost nets have no set target species. They simply fish anything that comes their way, as can be seen in the image to the right showing the release of a seal trapped in a ghost net. Ghost nets have even been reported to capture organisms of terrestrial origin for example a reindeer. The lost gear doesn’t even need to be wholly intact to continue fishing; it was observed that 2% of Australian Fur Seals were found entangled in parts of nets wrapped around their collars.

 

 

 

 

Ghost net caught on a reef structure kept upright by floats
Image of a gill net snagged on a reef structure, kept upright by it’s floats and the support of the reef. Photo credit: Tim Sheerman-Chase

Gill Nets:

Gill nets are commonly used for commercial fishing for species such as salmon, squid and tuna. They’re normally around 90m in length, and made up of monofilament mesh, which varies in size depending on the target fish species. The monofilament mesh is not easily detected by moving fish resulting in them swimming into the net and getting the mesh tangled in their gills preventing escape.  The simplicity of this net design is what makes it such a deadly threat to marine life; even after loss at sea, this net can successfully harvest fish and other marine species. In addition to this, the more organisms there are caught in the net, the more appealing the net becomes to other organisms, increasing the chance of a catch by acting as bait. It has been observed that free-floating gill nets can have an afterlife of anywhere between 30-590 days with the potential to cause the death of almost 2,000 individual organisms. These numbers increase if the net were to become tangled on a reef structure keeping it upright as seen in the image to the left, enabling the potential to ghost fish for more than 3 years after the date of loss. Between the years 1981-1985, it was estimated that lost gill nets in Northern Australian waters caused the death of almost 14,000 cetacean species.

 

 

Picture of a biodegradable fishing net complete with tag to track in case of loss
Picture of a tagged biodegradable fishing net as developed by Alejandro Plasencia for project Remora. Photo credit: Project Remora

Solutions:

Ghost fishing wasn’t regarded as a serious threat to marine life until well into the 1970’s, however methods of reducing the effects weren’t implemented until the mid-1980s, the first of which included the closure of an entire pelagic drift net fishery. Since then aside of the obvious aim to remove current ghost fishing gear, the main means of reducing ghost fishing have been by preventing the initial loss of nets. Often fishing gear is lost as its moorings are cut by boat propellers, or larger fishing gear is placed on top of smaller, so fishermen are encouraged to make their gear easily visible to avoid such collisions. With modern day technology it is possible to tag fishing gear so that it can be tracked if lost or misplaced. This is often coincided with suitable disposal services to remove and take care of old gear. Biodegradable materials are often used with the intention of lost fishing gear decomposing naturally to reduce impacts where preventing loss isn’t possible. Whilst these methods and up-to-date technologies are helping reduce the level of ghost fishing in the marine environment, they are costly. The image to the right is of a biodegradable fishing net implemented with a tag for tracking in case of loss, designed as part of project Remora.  Unfortunately, fisheries in developing countries are not likely to be able to afford such means, and so will still be contributing to the input of ghost nets. However, it has been said that fishermen from developing countries are more likely to search for and retrieve lost or damaged fishing gear as they can’t afford to replace them, whereas fisheries from well developed countries can afford to lose nets of any size.

 

 

Conclusions:

Ghost fishing is  the silent killer in the oceans. Marine animal populations are already under stress from intentional fishing and habitat destruction, be it from sea temperature and level rise or from dredging and trawling, that any extra stress needs to be addressed and sorted immediately. Projects have already started in regards to cleaning up the accumulation of ghost nets, but these efforts may be redundant if input of old and lost fishing gear into the marine environment isn’t halted completely. The below image shows the cycle of ghost fishing and demonstrates that the only way to stop the cycle and it’d destruction is through direct human intervention. If not for the sake of the diversity of the marine environment, then for the sake of a stable food source for both well developed and less developed countries, it is in everyone’s best interest that derelict fishing gear is put to rest on land, not in the sea.

Flow diagram showing the life cycle of ghost fishing nets
Detailed diagram of the different stages of ghost fishing from initial loss, to drifting and catching species, to those species being consumed resulting in the net being able to re-drift and catch again. Picture take from the Olive Ridley Project
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