Unsustainable fishing methods

Unsustainable fishing methods refers to the utilization of the various fishing methods in order to capture or harvest fish, at a rate which sees the declining of fish populations over time.[1][2] These methods are observed to facilitate the destructive fishing practices that destroy ecosystems within the ocean, and is used as a tool for over-fishing which results in the depletion of fish populations at a rate that cannot be sustained.[3]

Commercial fishing showing the abundance of fish species caught using a trawling method.

These unsustainable fishing methods vary in capabilities, ranging from commercial-grade equipment, such as bottom trawling, to consumer-grade equipment, such as fishing rods and nets.[4] It is the combination of these methods and increasing fishing pressures through sociological practices such as over-exploitation and over-fishing, which makes these fishing methods unsustainable.[5][6]

Defining unsustainable

The unsustainable nature of fisheries can be characterized by three aspects, as stated by Ray Hilborn:

  • Inconsistent long-term yield refers to the imbalance in nature when fishing is practised improperly, which results in the inability to capture the maximum sustainable yield at a regular and predictable rate.[7]
  • Endangering intergenerational equity relates to the destruction of ecosystems that requires more than one generation to reverse;[8] disallowing future generations the opportunity to capture that same yield.[7]
  • Destroying a biological, social, and economic system priorities the health of the human ecosystem or livelihood over that of the ocean’s biodiversity,[8] where the depletion of individual stock is carried out until the ecosystem’s intrinsic integrity is lost.[7]

Types of unsustainable fishing methods
Trawling devices depicted to operate at various ocean depths. Showing in particular, the vast amount of fish species caught within the "tangles".

Bottom trawling

Bottom trawling is classified as an active gear that consists of a large weighted net, which trawls or “drags” along the sea floor; acting as a destructive mechanism that removes coral and other marine species.[9][10] As stated by the Sea Fish Industry Authority,[9] the trawl consists of several components that assist the catch composition of the gear, which includes:

  • The otter boards which herd the fish into the trawl path by dragging up a “sand cloud” that creates a barrier of escape.[11]
  • The sweeps and bridles continue to herd the fish further into the trawl.
  • The wings and ground gear minimize the potential for fish to escape, which also tires the fish and enables them to drop into the body of the net.

Bottom trawling is scientifically divided into two types of trawling, demersal trawling and benthic trawling,[12] which allows trawlers to target species that live close to the seabed, or those that live on or in the seabed respectively.[9]

Cyanide fishing
The blast radius of an explosive device being set off underwater to obtain fish (dynamite fishing).

Cyanide fishing is used as a method to capture live fish to supply the international aquarium trade, and more recently, to supply the demand for live reef fish by restaurants.[13] This method involves the spraying of sodium cyanide into the targeted fish’s habitat as a means of stunning the fish without killing them.[14] For each fish captured using sodium cyanide, a square metre of coral reef is destroyed.[15]

Dynamite fishing

Dynamite fishing or blast fishing is a technique that detonates explosives underwater in order to easily kill schools of fish and maximize yield. The dead or stunned fish then floats to the surface of the water where they can be easily harvested.[15] Along with the fish, the entire ecosystem, such as coral reefs, and other marine organisms within the blast radius can be destroyed; which in the coral reef’s case, can take hundreds of years to rebuild.[16]

Ghost fishing
Sea turtle entangled in a ghost net.

Ghost fishing is classified as passive gear that occurs when fishing gear has been left or lost in the ocean.[9][17] The gear can potentially continue to catch or entangle any species of marine life as it  drifts through the water or snags on rocky reef, eventually killing the entangled organism through laceration, suffocation or starvation.[18]

By-catch obtained when targeting shrimps, showing the vast amount of by-catch in fisheries.

By-catch

By-catching is an inevitable aspect of fishing where unwanted fish or other marine organisms including turtles, dolphins and juveniles are caught.[19] This is a by-product of the unselective nature of modern fishing gear, such as bottom trawling which captures everything in the path of the net.[20] Consumer-grade gear such as fishing rods and nets are used by pirate fishers to undertake illegal, unreported and unregulated fishing which adds to the number of marine species taken from their ecosystems.[15]

Evidence that these methods are unsustainable

Examples of the use of unsustainable fishing methods exist globally and not only impacts the harvested species, but also all marine species that coexist or rely on the targeted harvest.[21]

  • Bottom trawling in Canadian waters have shown the destructive effects of the fishing method. With the establishment of Baffin Bay fishery in 1996, feeding grounds for narwhals in the Canadian Arctic are shown to be impacted by vast benthic damage as a result of bottom trawling.[22] Hence why leading marine environmentalists describes bottom trawling as a 'great harm' to fisheries.[23]
  • In the 1960s, the commercial use of poisons such as sodium cyanide (cyanide fishing), were used throughout Southeast Asia to serve the market demand for high-value coral fish.[14] This has evidently impacted the local ecosystem through coral bleaching and the killing of untargeted species.[24]
  • The use of dynamite fishing or blast fishing is evident in coastal regions of Tanzania.[25] The vast use of this method in the region has seen marine scientists, international environmental NGOs, and environment activists label the practice as destructive and unsustainable.[25] The profit from their catches is described to be a factor in the continual use of the dangerous practice.[26]
  • During the period between 2000 and 2001, a field study was conducted in Oman to simulate the catch rate of fishing gear that has been lost in the ocean (ghost fishing), by setting nets at various depths in fishing grounds across cities in Oman.[27] The study found that the mortality rate as a result of these simulated tests, estimated to 1.3kg per a trap, per a day.[27] This evaluated to a predicted mortality rate of 78.4kg per a lost gear, over 6 months.[27]
  • A study conducted in the Glover’s Reef Marine Reserve, Belize, between 2004-2010 and 2011-2017, found that the mortality rates for most species were much higher than the natural mortality rate.[28] This is a result of over-fishing with the main gears being used in those regions consisting of spears and fishing rods.[28] By-catching was also observed through the frequent catching of immature grouper and snapper species.[28]

Mitigation using sustainable methods

Concerns over the unsustainable nature of the use of these fishing methods have been identified by the United Nations Convention on the Law of the Sea treaty which focuses attention on over-fishing through the use of these methods.[29] According to the United Nations convention agreements in exclusive economic zones (1994):[30]

  • Article 61 focuses on the “conservation of the living resources” which obligates the coastal state to properly conserve and manage its living resources to ensure that these resources are not over-exploited. The state is also obligated to maintain maximum sustainable yield of harvested populations whilst also taking into consideration other species that are associated or depend on that harvested population.
  • Article 62 concerns the “utilization of the living resources” in relations to the governing of harvesting those living resources within the coastal state’s exclusive economic zone. This includes the enforcement of conservation measures, such as the licensing of fishing vessels and equipment,  regulating the type, size and amount of gear used and permitting the landing of all or any part of the catch in ports.
  • Article 65 relates to “marine mammals” and the rights of the coastal state to prohibit, limit, or regulate the exploitation of marine animals.


These convention agreements are recognized by global fisheries that resultantly employ harvest strategies and guidelines, such as gear restrictions and deployment limits,[31] to maintain the use of these unsustainable fishing methods. Examples of such strategies and guidelines employed by global fisheries are listed below:

  • The Australian Fisheries Management Authority (AFMA) recognizes the impact that bottom trawlers may have on sensitive habitat areas, like reef structures (AFMA, 2020).[32] As a result, management arrangements that include the compulsory use of physical devices, such as by-catch reduction devices (BRD) within trawls, ensures that the use of trawl poses the least environmental impact.[32] BRDs minimizes the by-catch of many species of juveniles, by using a minimum sized mesh which enables untargeted fish species to escape the trawl net.[33]
  • Fisheries and Oceans Canada identifies ghost fishing as a major threat to the marine ecosystem.[34] Resultantly, Canadian fisheries have implemented a cooperative strategy with harvesters, to undertake ghost-gear removal.[34] This extends to the implementation of compulsory reporting of lost fishing gear and the active seeking of mitigation methods that may reduce the occurrence and impact of ghost fishing.[34]
  • The National Oceanic and Atmospheric Administration fisheries (NOAA fisheries) in the United States of America, describes by-catch as a global issue that threatens the sustainability of fishing communities.[35] The NOAA fisheries has implemented a National Bycatch Reduction Strategy that incorporates 3 major laws.[36] In accordance to these laws, US fisheries have put in place regulations that require trawling vessels  to use turtle excluder devices (TEDs) that will mitigate the capture of turtles in the trawl nets.[36] This also extends to the enabling of the use of additional TEDs and promoting the use of sustainable fishing practices.[36] The 3 major laws include:
  • The Philippines fisheries code Republic Act 10654, was amended in 2015 in recognition of the region’s over-exploitation of unreported and unregulated fishing.[37] The Act was amended in the Philippine’s pursuit to comply with international conventions, in order to converse and manage fish species and resources.[37] Section 92 relates to fishing through explosives (dynamite fishing) and poisonous substances (cyanide fishing), stating that the use of these methods will result in an administrative fine and/or imprisonment upon conviction by a court of law.[37]  

Obstacles for mitigation
Parrot-fish (Sparisoma viride) shown to be lined up at a market.

As fisheries are important both socially and economically, it is difficult to maintain a socio-economic sustainable management system, which considers the environmental impact of fishing methods; particularly in under-developed regions where communities rely on fisheries for their livelihood.[38] An observed trend between fisheries in under-developed regions, is that those regions lack fisheries management and enforcement, and when compared to well-developed and well-managed regions in the world, under-developed regions, on average, account for 3-fold greater harvest rates.[39]


This shows an obstacle for the mitigation of unsustainable fishing methods, which is observed to be influenced by a social-ecological trade off.[40] In developing regions in world where communities are classified as low-income, fisheries are a means of both food security and income,[41] and with the enforcement of regulations and management, the livelihoods of people within those communities are at stake.[40] This impact can be observed through the closed fishing season policy for sardines in the Philippines.[42] The immediate loss of income to the fisheries worker’s low-income households, eroded the favourability of the policy amongst the community; which also poses an implementation issue for future policies and regulations.[42]

The challenge of pursuing environmental-based objectives, is the simultaneous maintenance of social sustainability.[43] It has been identified that social factors through social conception of human well-being, have the potential to improve the implementation of fisheries regulation and governance.[44] This remains a difficult concept in developing fishery regions, such as the Caribbean coral reef fishery, where the implementation of management and regulation upon parrot-fish (Sparisoma viride), has seen an initial decrease in income for fishery workers who rely heavily on the species.[40] To low income communities, this decrease in income is observed to drastically undermine the management of fisheries.[45]


In particular, when there exists a high demand and price in global markets for specific fish species, low income communities who have access to those specific species have been observed to be the main cause of over-fishing.[13]  In a region where fishermen have fewer alternatives to earn an income, and where fishery regulation and management have weak control, over-fishing of highly desired fish species is observed to be the best option for improving social well-being; despite the environmental impact.[46] This coincides with illegal fishing practices (pirate fishing) that is fuelled by the global demand for exotic seafood.[47]

Countries highlighted in blue implement a flag of convenience for their international vessels.


Pirate fishing fostered by the Flags of convenience that allow vessels to operate under a state’s flag where there exists limited fisheries regulations or laws, enables fishing vessels the ability to practise illegal, unreported and unregulated fishing.[48] This U.S. $1.2 billion-dollar industry poses a drastic impact on global fish populations and blatantly undermines the international rules of conversation and management of the high seas resources, according to Ian Macdonald, Australian Minister for Fisheries, Forestry and Conservation (2003-2010).[48] Illegal and unreported fishing contributes to the reduction in fish stocks and hinders the ability for fish populations to recover. It is believed that between 10 billion and 23 billion incidences of illegal and unreported fishing happen annually, with communities in developing countries being more likely to partake in these illegal activities.[49]

See also

References
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  4. "Fishing methods and gear types | Marine Stewardship Council | Marine Stewardship Council". www.msc.org. Retrieved 2020-05-29.
  5. Vosooghi, Sareh (2019). "Panic-Based Overfishing in Transboundary Fisheries". Environmental & Resource Economics. 73 (4): 1287–1313. doi:10.1007/s10640-018-0299-8. ISSN 0924-6460.
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  8. Expert Meeting on Impacts of Destructive Fishing Practices, Unsustainable Fishing, and Illegal, Unreported and Unregulated (IUU) Fishing on Marine Biodiversity and Habitats 2009 Rom (2010). Report of the FAO/UNEP Expert Meeting on Impacts of Destructive Fishing Practices, Unsustainable Fishing, and Illegal, Unreported and Unregulated (IUU) Fishing on Marine Biodiversity and Habitats : Rome, 23 - 25 September 2009. Food and Agriculture Organization, FAO/UNEP Expert Meeting on Impacts of Destructive Fishing Practices, Unsustainable Fishing, and Illegal, Unreported and Unregulated (IUU) Fishing on Marine Biodiversity and Habitats (2009.09.23-25 Rome). Rome. ISBN 978-92-5-106533-4. OCLC 838671675.CS1 maint: multiple names: authors list (link)
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  23. BBC NEWS | Science/Nature | Deep-sea trawling's 'great harm' - By Richard Black (Last Updated: Wednesday, 6 October 2004, 10:03 GMT 11:03 UK)BBC science correspondent
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Further reading
  • Ferguson-Cradler, Gregory. "Fisheries’ collapse and the making of a global event, 1950s–1970s." Journal of Global History 13.3 (2018): 399-424. online
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