Figure 1. A visualisation of the quantity of fish that purse-seine net fishing can capture (source).
Figure 1. A visualisation of the quantity of fish that purse-seine net fishing can capture (source).

A multitude of fishing methods are used to capture fish for human consumption. These range from passive fishing gear such as lobster pots or gill nets, all the way to active fishing gear such as large purse-seine nets that can capture fish in large quantities. We are all aware that over fishing may be coming an issue with sustaining fish stocks, but what you may not know is the effects that the fishing gear themselves are having on the marine environment. The nets used for fishing were at one time made of cotton, this is susceptible to rotting and so many now have converted to using nylon instead, a material that does not decompose. It is this material that is causing an ocean wide problem that is commonly known as ‘ghost fishing’.

What is ghost fishing?

Underwater image examples of ghost fishing in action. a) Shows an octopus trapped in a cage designed to encapture finfish. b) Shows a rabbitfish that has injured/ lost its mouth and nose due to continues bumping against the mesh caging. c) A gillnet that is entangled around rocks with a lobster caught inside the net. d) The bones of finfish where a gillnet lays (source).
Figure 2. Underwater image examples of ghost fishing in action. a) Shows an octopus trapped in a cage designed to encapture finfish. b) Shows a rabbitfish that has injured/ lost its mouth and nose due to continues bumping against the mesh caging. c) A gillnet that is entangled around rocks with a lobster caught inside the net. d) The bones of finfish where a gillnet lays (source).

The term ‘ghost fishing’ is a term used to describe fishing gear that will continue to capture and inevitably kill fish species when the gear has been lost at sea. This loss can be accidental or may be discarded by the fisher on purpose if the net is damaged. It has been estimated that less than 1% of fishing nets from EU fishers are lost a year, however this is still a total length of around 209 km of fishing nets lost. Also this figure is just for EU fishers and not a global estimate which would be higher. Despite this small fraction of net loss, it still has the potential to ‘ghost fish’. If a lobster fishing pot, for example, cannot be found by the fisher and is left in the sea, the bait inside will still attract lobsters and other animals. If this lobster cannot escape it will eventually die and this will attract more animals in the pot; this attraction and capture will continue until the pot breaks down or decomposes. Evidence from a controlled study suggests that lobster fishing pots have the potential to continue fishing for periods of two years after the original bait has been eaten.

Large animals are also at risk from ghost fishing gear such as seals. Seals can become entangled and the fishing net can form a ‘neck collar’; 40% of all neck collars in the waters of Tasmania were from trawl nets with 73% causing physical pain to the animals. 1478 seals and sea lions a year die in South Australian waters as a result of entanglement. Entanglement has also been recorded in sea turtles and most records show that entanglement in turtles is due to fishing gear; e.g. gillnets or trawl nets from commercial fishing activity.

Longevity of ghost fishing gear

The longevity of the functioning ‘ghost’ fishing net varies between individual nets, depending on where the net is lost and the conditions the net is faced with. A controlled study by Erzini et al (1997) found that the lifetime of a fishing gill net that has been lost is between 15 and 20 weeks, meaning that the net will continue to fish for this period of time even after the net is lost. However, after 8 – 11 months the nets had stopped functioning and had been colonised by algae. This length of time is not always true though, as another experimental study on ghost gillnets found that even though catch effieciency will decrease over time (to around 5% the original catch rates) they can still continue to fish; this decreased rate of fishing was observed 27 months after the nets were deployed and evidence showed that it may have continued beyond this period.

Ghost fishing gear can entangle air breathing marine animals such as these sea lions which will eventually drown if not rescued (source).
Figure 3. Ghost fishing gear can entangle air breathing marine animals such as these sea lions that will eventually drown if not rescued fast enough (source).

Even wider than ghost fishing …

Rogue fishing equipment not only poses the threat of continual fishing, but it also has a wider impact on marine organisms. Possatto et al (2011) found nylon fragments from fishing gear in the stomachs of 23% of marine catfish sampled in a Brazilian estuary; research has shown that plastics such as nylon have the potential to carry harmful chemicals which can be harmful for the animals that ingest them. It has also been noted that waste fishing gear may eventually cause international conflicts; fishing nets have the potential to travel long distances from the site of release to a settling place (e.g. a coral reef). This could conflicts between the country trying to help protect their reef and the origin country of the fishing net.

Future management of ghost gear

I feel the most obvious solution to ghost fishing would simply to prevent the loss of fishing gear, but obviously this would be no easy feat. However, the Food and Agricultural Organisation of the United Nations (FAO) has supplied a set of guidelines for responsible fishing; one of these guidelines is that fishing gear should be marked with the details of the fisher, so that if fishing gear is lost it can easily be traced back to the owner. This, however, is only a set of guidelines which means that it is hard to enforce on a global scale. More effort needs to be spent in order to tackle this problem of lost fishing gear and the subsequent problem of ‘ghost fishing’.

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