Atlantic cod stocks were severely overfished in the 1970s and 1980s, leading to their abrupt collapse in 1992

Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans.

Ultimately overfishing can lead to resource depletion in cases of subsidised fishing, low biological growth rates and critical low biomass levels (e.g. by critical depensation growth properties). For example, overfishing of sharks has led to the upset of entire marine ecosystems.[1]

The ability of a fishery to recover after overfishing depends on whether the ecosystem conditions are suitable for the recovery. Dramatic changes in species composition can result in an ecosystem shift, where other equilibrium energy flows involve species compositions other than those that had been present before. For example, once trout have been overfished, carp might take over in a way that makes it impossible for the trout to re-establish a breeding population.



There are three recognized types of overfishing: growth overfishing, recruit overfishing and ecosystem overfishing.

  • Growth overfishing – is when fish are harvested at an average size that is smaller than the size that would produce the maximum yield per recruit. This makes the total yield less than it would be if the fish were allowed to grow to a reasonable size. It can be countered by reducing fishing mortality to lower levels and increasing the average size of the fish harvested to a length that will allow maximum yield per recruit.[2]
  • Recruit overfishing – is when the mature adult (spawning biomass) population is depleted to a level where it no longer has the reproductive capacity to replenish itself. There are not enough adults to produce offspring.[2] Increasing the spawning stock biomass to a target level is the approach taken by managers to restore an overfished population to sustainable levels. This is generally accomplished by placing moratoriums, quotas and minimum size limits on a fish population.
  • Ecosystem overfishing – is when the balance of the ecosystem is altered due to overfishing. Declines in the abundances of large predatory species declines and in turn small forage type species increase in abundance, causing a shift in the balance of the ecosystem towards smaller species of fish.


Fishing down the food web

Examples of the outcomes from overfishing exist in areas such as the North Sea of Europe, the Grand Banks of North America and the East China Sea of Asia.[3] In these locations, overfishing has not only proved disastrous to fish stocks but also to the fishing communities relying on the harvest. Like other extractive industries such as forestry and hunting, fishery is susceptible to economic interaction between ownership or stewardship and sustainability, otherwise known as the tragedy of the commons.

  • The Peruvian coastal anchovy fisheries crashed in the 1970s after overfishing and an El Niño season[4] largely depleted anchovies from its waters.[5][6] Anchovies were a major natural resource in Peru; indeed, 1971 alone yielded 10.2 million metric tons of anchovies. However, the following five years saw the Peruvian fleet's catch amount to only about 4 million tons.[4] This was a major loss to Peru's economy.
  • The collapse of the cod fishery off Newfoundland,[7] and the 1992 decision by Canada to impose an indefinite moratorium on the Grand Banks, is a dramatic example of the consequences of overfishing.[8]
  • The sole fisheries in the Irish Sea, the west English Channel, and other locations have become overfished to the point of virtual collapse, according to the UK government's official Biodiversity Action Plan. The United Kingdom has created elements within this plan to attempt to restore this fishery, but the expanding global human population and the expanding demand for fish has reached a point where demand for food threatens the stability of these fisheries, if not the species' survival.
  • Many deep sea fish are at risk, such as orange roughy, Patagonian toothfish and sablefish. The deep sea is almost completely dark, near freezing and has little food. Deep sea fish grow slowly because of limited food, have slow metabolisms, low reproductive rates, and many don't reach breeding maturity for 30 to 40 years. A fillet of orange roughy at the store is probably at least 50 years old. Most deep sea fish are in international waters, where there are no legal protections. Most of these fish are caught by deep trawlers near seamounts, where they congregate because of food. Flash freezing allows the trawlers to work for days at a time, and modern fishfinders target the fish with ease.[9]
  • Blue walleye went extinct in the Great Lakes in the 1980s. Until the middle of the 20th century, it was a commercially valuable fish, with about a half million tonnes being landed during the period from about 1880 to the late 1950s, when the populations collapsed, apparently through a combination of overfishing, anthropogenic eutrophication, and competition with the introduced rainbow smelt.


According to a 2008 UN report, the world's fishing fleets are losing $50 billion USD each year through depleted stocks and poor fisheries management. The report, produced jointly by the World Bank and the UN Food and Agriculture Organization (FAO), asserts that half the world's fishing fleet could be scrapped with no change in catch. In addition, the biomass of global fish stocks have been allowed to run down to the point where it is no longer possible to catch the amount of fish that could be caught.[10] Increased incidence of schistosomiasis in Africa has been linked to declines of fish species that eat the snails carrying the disease-causing parasites.[11] Massive growth of jellyfish populations threaten fish stocks, as they compete with fish for food, eat fish eggs, and poison or swarm fish, and can survive in oxygen depleted environments where fish cannot; they wreak massive havoc on commercial fisheries. Overfishing eliminates a major jellyfish competitor and predator exacerbating the jellyfish population explosion.

Acceptable levels

The notion of overfishing hinges on what is meant by an acceptable level of fishing. More precise biological and bioeconomic terms define acceptable level as follows:

  • Biological overfishing occurs when fishing mortality has reached a level where the stock biomass has negative marginal growth (slowing down biomass growth), as indicated by the red area in the figure. (Fish are being taken out of the water so quickly that the replenishment of stock by breeding slows down. If the replenishment continues to slow down for long enough, replenishment will go into reverse and the population will decrease.)
  • Economic or bioeconomic overfishing additionally considers the cost of fishing when determining acceptable catches. Under this framework a fishery is considered to be overfished when catches exceed maximum economic yield where resource rent is at its maximum. Fish are being removed from the fishery so quickly that the profitability of the fishery is sub-optimal. A more dynamic definition of economic overfishing also considers the present value of the fishery using a relevant discount rate to maximise the flow of resource rent over all future catches.
The Traffic Light colour convention, showing the concept of Harvest Control Rule (HCR), specifying when a rebuilding plan is mandatory in terms of precautionary and limit reference points for spawning biomass and fishing mortality rate.

Harvest control rule

A current model for predicting acceptable levels is the Harvest Control Rule (HCR), which is a variable over which management has some direct control as a function of some indicator of stock status. Constant catch and constant fishing mortality are two types of simple harvest control rules.[12]

Input and output orientations

Fishing capacity can also be defined following an input or an output orientation.

  • An input-oriented fishing capacity is defined as the maximum available capital stock in a fishery that is fully utilized at the maximum technical efficiency in a given time period, given resource and market conditions.[13]
  • An output-oriented fishing capacity is defined as the maximum catch a vessel (fleet) can produce if inputs are fully utilized given the biomass, the fixed inputs, the age structure of the fish stock, and the present stage of technology.[14]

Technical efficiency of each vessel of the fleet is assumed necessary to attain this maximum catch. The degree of capacity utilization results from the comparison of the actual level of output (input) and the capacity output (input) of a vessel or a fleet.


With present and forecast levels of the world population it is not possible to solve the overfishing issue;[citation needed] however, there are mitigation measures that can save selected fisheries and forestall the collapse of others.

In order to meet the problems of overfishing, a precautionary approach and Harvest Control Rule (HCR) management principles have been introduced in the main fisheries around the world. The Traffic Light colour convention introduces sets of rules based on predefined critical values, which could be adjusted as more information is gained.

The "United Nations Convention on the Law of the Sea" treaty deals with aspects of overfishing in articles 61, 62, and 65.[15]

  • Article 61 requires all coastal states to ensure that the maintenance of living resources in their exclusive economic zones is not endangered by over-exploitation. The same article addresses the maintenance or restoration of populations of species above levels at which their reproduction may become seriously threatened.
  • Article 62 provides that coastal states: "shall promote the objective of optimum utilization of the living resources in the exclusive economic zone without prejudice to Article 61"
  • Article 65 provides generally for the rights of, inter alia, coastal states to prohibit, limit, or regulate the exploitation of marine mammals.

Overfishing can be viewed as a case of the tragedy of the commons; in that sense, solutions would promote property rights, such as privatization and fish farming. Daniel K. Benjamin, in Fisheries are Classic Example of the "Tragedy of the Commons", cites research by Grafton, Squires, and Fox to support the idea that privatization can solve the overfishing problem:[16]

According to recent research on the British Columbia halibut fishery, where the commons has been at least partly privatized, substantial ecological and economic benefits have resulted. There is less damage to fish stocks, the fishing is safer, and fewer resources are needed to achieve a given harvest.

Another possible solution, at least for some areas, is fishing quotas, so fishermen can only legally take a certain amount of fish. A more radical possibility is declaring certain areas of the sea "no-go zones" and make fishing there strictly illegal, so the fish in that area have time to recover and repopulate.

Controlling consumer behavior and demand is a key in mitigating action. Worldwide a number of initiatives emerged to provide consumers with information regarding the conservation status of the seafood available to them. The Guide to Good Fish Guides lists a number of these.

Fishing quotas

A model of the interaction between fish and fishers showed that when an area is closed to fishers, but there are no catch regulations such as individual transferable quotas, fish catches are temporarily increased but overall fish biomass is reduced, resulting in the opposite outcome than the one desired for fisheries.[17] Thus, a displacement of the fleet from one locality to another will generally have little effect if the same quota is taken. As a result, management measures such as temporary closures or establishing a Marine Protected Area of fishing areas are ineffective when not combined with individual fishing quotas. An inherent problem with quotas is that fish populations vary from year to year. A study has found that fish populations rise dramatically after stormy years due to more nutrients reaching the surface and therefore greater primary production.[18] To fish sustainably quotas need to be changed each year to take account of the population of fish but this is difficult to do.

Individual transferable quotas

Individual transferable quotas (ITQs) are fishery rationalization instruments defined under the Magnuson-Stevens Fishery Conservation and Management Act as limited access permits to harvest quantities of fish. Fisheries scientists decide the optimal amount of fish (total allowable catch) to be harvested in a certain fishery, taking into account carrying capacity, regeneration rates and future values. Under ITQs, members of a fishery are granted rights to a percentage of the total allowable catch which can be harvested each year. These quotas can be fished, bought, sold, or leased allowing for the least cost vessels to be used. ITQs are used in New Zealand, Australia, Iceland, Canada and the United States. Only three ITQ programs have been implemented in the United States due to a moratorium supported by Ted Stevens.

In 2008 a large scale study of fisheries that used ITQ's and ones that didn't provided strong evidence that ITQ's can help to prevent collapses and restore fisheries that appear to be in decline.[19][20][21][22]

Fishing suspension

China bans fishing in the South China Sea for a period each year.[23]

Benefits of underfishing

Deliberately underfishing to increase long term fish stocks has been proposed as a way fisherman can maximize their yields in the long run.[24]

Resistance from fishermen

There is always disagreement between fishermen and government scientists... Imagine an overfished area of the sea in the shape of a hockey field with nets at either end. The few fish left therein would gather around the goals because fish like structured habitats. Scientists would survey the entire field, make lots of unsuccessful hauls, and conclude that it contains few fish. The fishermen would make a beeline to the goals, catch the fish around them, and say the scientists do not know what they are talking about. The subjective impression the fishermen get is always that there's lots of fish - because they only go to places that still have them... fisheries scientists survey and compare entire areas, not only the productive fishing spots.[25]Fisheries scientist Daniel Pauly

  • The fishing capacity problem is not only related to the conservation of fish stocks but also to the sustainability of fishing activity. Causes of the fishing problem can be found in property rights regime of fishing resources. Overexploitation and rent dissipation of fishermen arise in open-access fisheries as was shown in Gordon.[26][27]
  • In open-access resources like fish stocks, in the absence of a system like individual transferable quotas, the impossibility of excluding others provokes the fishermen who want to increase catch to do so effectively by taking someone else' share, intensifying competition. This tragedy of the commons provokes a capitalization process that leads them to increase their costs until they are equal to their revenue, dissipating their rent completely.

Removal of subsidies

Several scientists have called for an end to subsidies paid to deep sea fisheries. In international waters beyond the 200 nautical mile exclusive economic zones of coastal countries, many fisheries are unregulated, and fishing fleets plunder the depths with state-of-the-art technology. In a few hours, massive nets weighing up to 15 tons, dragged along the bottom by deep-water trawlers, can destroy deep-sea corals and sponge beds that have taken centuries or millennia to grow. The trawlers can target orange roughy, grenadiers or sharks. These fish are usually long-lived and late maturing, and their populations take decades, even centuries to recover.[28]

Fisheries scientist Daniel Pauly and economist Ussif Rashid Sumaila have examined subsidies paid to bottom trawl fleets around the world. They found that $152 million US per year are paid to deep-sea fisheries. Without these subsidies, global deep-sea fisheries would operate at a loss of $50 million a year. A great deal of the subsidies paid to deep-sea trawlers is to subsidize the large amount of fuel required to travel beyond the 200 mile limit and drag weighted nets.[28]

  • "There is surely a better way for governments to spend money than by paying subsidies to a fleet that burns 1.1 billion litres of fuel annually to maintain paltry catches of old growth fish from highly vulnerable stocks, while destroying their habitat in the process" – Pauly.
  • "Eliminating global subsidies would render these fleets economically unviable and would relieve tremendous pressure on over-fishing and vulnerable deep-sea ecosystems" – Sumaila.

Consumer awareness

Sustainable seafood is a movement that has gained momentum as more people become aware about overfishing and environmentally destructive fishing methods. Sustainable seafood is seafood from either fished or farmed sources that can maintain or increase production in the future without jeopardizing the ecosystems from which it was acquired. In general, slow-growing fish that reproduce late in life, such as orange roughy, are vulnerable to overfishing. Seafood species that grow quickly and breed young, such as anchovies and sardines, are much more resistant to overfishing. Several organizations, including the Marine Stewardship Council (MSC), and Friend of the Sea, certify seafood fisheries as sustainable.

The Marine Stewardship Council (MSC) has developed an environmental standard for sustainable and well-managed fisheries. Environmentally responsible fisheries management and practices are rewarded with the use of its blue product ecolabel. Consumers concerned about overfishing and its consequences are increasingly able to choose seafood products which have been independently assessed against the MSC's environmental standard and labelled. This enables consumers to play a part in reversing the decline of fish stocks. As of April 2010, 69 fisheries around the world have been independently assessed and certified as meeting the MSC standard. Their where to buy page lists the currently available certified seafood - as of April 2010 nearly 4,000 MSC-labelled products are available in over 60 countries around the world. Fish & Kids is an MSC project to teach schoolchildren about marine environmental issues, including overfishing.

The Monterey Bay Aquarium's Seafood Watch Program, although not an official certifying body like the MSC, also provides guidance on the sustainability of certain fish species:[29] Some seafood restaurants have begun to offer more sustainable seafood options. The Seafood Choices Alliance is an organization whose members include chefs that serve sustainable seafood at their establishments. In the US, the Sustainable Fisheries Act defines sustainable practices through national standards. Although there is no official certifying body like the MSC, the National Oceanic and Atmospheric Administration has created FishWatch to help guide concerned consumers to sustainable seafood choices. See also a guide to good fish guides.

Fish farming

In 2009, researchers in Australia managed for the first time to coax southern bluefin tuna to breed in landlocked tanks, opening up the possibility of using fish farming as a way to save the species from the problems of overfishing in the wild.[30]


Daniel Pauly, a fisheries scientist well known for pioneering work on the human impacts on global fisheries, comments:

"It is almost as though we use our military to fight the animals in the ocean. We are gradually winning this war to exterminate them. And to see this destruction happen, for nothing really – for no reason – that is a bit frustrating. Strangely enough, these effects are all reversible, all the animals that have disappeared would reappear, all the animals that were small would grow, all the relationships that you can't see any more would re-establish themselves, and the system would re-emerge. So that's one thing to be optimistic about. The oceans, much more so than the land, are reversible..."[31]

See also


  1. ^ Shark Declines Threaten Shellfish Stocks, Study Says", National Geographic News. 29 March 2007.
  2. ^ a b Pauly 1983
  3. ^ Pollution, overfishing destroy East China Sea fishery, GOV.cn, August 16, 2006
  4. ^ a b "Peruvian Anchovy Case: Anchovy Depletion and Trade," Trade and Environment Database, 1999.
  5. ^ "Foreign Assistance Legislation for Fiscal Year 1982," Committee on Foreign Affairs, 1981.
  6. ^ "Peru - Fishing," Federal Research Division of the U.S. Library of Congress.
  7. ^ Kunzig R (1995) "Twilight of the Cod" Discover, April 1995, p. 52.
  8. ^ ch 11-12. Mark Kurlansky (1997). Cod: A Biography of the Fish That Changed the World. New York: Walker. ISBN 0-8027-1326-2.
  9. ^ AAAS (2007) Long-lived deep-sea fishes imperilled by technology, overfishing
  10. ^ Fisheries waste costs billions BBC News, 8 October 2008.
  11. ^ Overfishing Is Emptying World's Rivers, Lakes, Experts Warn, James Owen, National Geographic News
  12. ^ Coad, Brian W and McAllister, Don E (2008)Dictionary of Ichthyology.
  13. ^ * Kirkley, J.E. and Squires, D. (1999) Capacity and Capacity Utilization in Fishing Industries, Discussion paper 99-16, Department of Economics, University of California, San Diego.
  14. ^ * Vestergaard, N.; Squires, D.; Kirkley, J.E. (2003). "Measuring Capacity and Capacity Utilization in Fisheries. The Case of the Danish Gillnet Fleet". Fisheries Research 60 (2–3): 357–68. doi:10.1016/S0165-7836(02)00141-8. 
  15. ^ Text of the United Nations Convention on the Law of the Sea: Part V
  16. ^ Benjamin, Daniel K (2001). "Fisheries are Classic Example of the Tragedy of the Commons," PERC Reports, 19(1).
  17. ^ "Moustakas, A., Silvert, W. and Dimitromanolakis A. (2006). A spatially explicit learning model of migratory fish and fishers for evaluating closed areas. Ecological Modelling, 192: 245-258."]. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBS-4H2PJVB-2&_user=10&_coverDate=02%2F15%2F2006&_rdoc=16&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235934%232006%23998079998%23615793%23FLA%23display%23Volume)&_cdi=5934&_sort=d&_docanchor=&view=c&_ct=25&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f86fb6039ae74a702f876edfec9d2f2d. 
  18. ^ Aria Pearson New Scientist 06 January 2009 Why storms are good news for fishermen
  19. ^ Costello et al.
  20. ^ New Scientist: Guaranteed fish quotas halt commercial free-for-all
  21. ^ A Rising Tide: Scientists find proof that privatising fishing stocks can avert a disaster The Economist, 18th Sept, 2008.
  22. ^ New study offers solution to global fisheries collapse Eureka alert.
  23. ^ South China Sea fishing ban "indisputable": foreign ministry spokesman Chinaview, 9 June 2009.
  24. ^ Tierney, John (2007-12-06). "A Win-Win for Fish and Fishermen". The New York Times. http://tierneylab.blogs.nytimes.com/2007/12/06/a-win-win-for-fish-and-fishermen/?hp. 
  25. ^ Fisherman Life (2008) An interview with Daniel Pauly by Margaret Boyes
  26. ^ Gordon, H. S. (1953). "An Economic Approach to the optimum utilization of Fishery Resources". Journal of the Fisheries Research Board of Canada 10 (7): 442–57. doi:10.1139/f53-026. 
  27. ^ Gordon, H.S. (1954). "The Economic Theory of a Common-Property Resource: The Fishery". Journal of Political Economy 62 (2): 124–42. doi:10.1086/257497. 
  28. ^ a b AAAS (2007) The last wild hunt – Deep-sea fisheries scrape bottom of the sea
  29. ^ Monterey Bay Aquarium: Seafood Watch Program - Frequently Asked Questions
  30. ^ The Top 10 Everything of 2009: Top 10 Scientific Discoveries: 5. Breeding Tuna on Land, Time magazine, December 8, 2009
  31. ^ Fisheries on the brink – Youtube: Daniel Pauly


External links

External images
Biomass distributions for high trophic-level fishes in the North Atlantic, 1900–2000 Flash animation from The Sea Around Us

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Look at other dictionaries:

  • overfishing — ● overfishing nom masculin (anglais overfishing) Synonyme de surpêche. ● overfishing (synonymes) nom masculin (anglais overfishing) Synonymes : surpêche …   Encyclopédie Universelle

  • overfishing — UK [ˌəʊvə(r)ˈfɪʃɪŋ] US [ˌoʊvərˈfɪʃɪŋ] noun [uncountable] fishing that damages a river or an area of sea because too many fish are caught Thesaurus: hunting, shooting and fishinghyponym …   Useful english dictionary

  • overfishing — 1) a level of fishing effort or fishing mortality such that a reduction of this level would, in the medium term, lead to an increase in the total catch. For long lived species, overfishing starts well before the stock becomes overfished. See also …   Dictionary of ichthyology

  • overfishing — Current fishing levels may not be sustainable, and yields may be higher in the long term if the fishing level is reduced in the short term. This may be due either to growth overfishing or recruitment overfishing. Classification of a stock as… …   Fisheries — dictionary

  • overfishing — noun fishing that reduces the stock of remaining fish in an area to below that which is acceptable …   Wiktionary

  • overfishing — o·ver·fi·shing s.m.inv. ES ingl. {{wmetafile0}} TS ecol. pesca incontrollata che può compromettere irrimediabilmente i meccanismi naturali di riproduzione dell ambiente ittico di un tratto di mare o di un corso d acqua, provocando la scomparsa di …   Dizionario italiano

  • overfishing — o|ver|fish|ing [ˌəuvəˈfıʃıŋ US ˌouvər ] n [U] the process of taking too many fish from the sea, a river etc, so that the number of fish in it becomes too low …   Dictionary of contemporary English

  • overfishing — v. fish too much, remove too many fish from the sea (causing a reduction in the number of fish and danger of extinctions) …   English contemporary dictionary

  • overfishing — UK [ˌəʊvə(r)ˈfɪʃɪŋ] / US [ˌoʊvərˈfɪʃɪŋ] noun [uncountable] fishing that damages a river or an area of sea because too many fish are caught …   English dictionary

  • overfishing limit — the point at which fishing seriously compromises continued and sustained productivity. May be determined from biological, economic and sociological considerations relevant to that particular fishery …   Dictionary of ichthyology

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