Overfishing

Source: Wikipedia, the free encyclopedia.
Jack mackerel caught by a Chilean purse seiner
Fishing down the food web

Overfishing is the removal of a species of

overfishing of sharks, has led to the upset of entire marine ecosystems.[1]
Types of overfishing include growth overfishing, recruitment overfishing, and ecosystem overfishing.

The ability of a fishery to recover from overfishing depends on whether its overall

ecosystem shift, where other equilibrium energy flows involve species compositions different from those that had been present before the depletion of the original fish stock. For example, once trout have been overfished, carp might exploit the change in competitive
equilibria and take over in a way that makes it impossible for the trout to re-establish a breeding population.

Since the growth of global

benthic species that do not recover quickly, and that provide a habitat for commercial fisheries species. This destruction alters the functioning of the ecosystem and can permanently alter species' composition and biodiversity. Bycatch, the collateral capture of unintended species in the course of fishing, is typically returned to the ocean only to die from injuries or exposure. Bycatch represents about a quarter of all marine catch. In the case of shrimp
capture, the bycatch is five times larger than the shrimp caught.

A report by

consumer awareness
.

Scale

Darker shades mean less overfishing, lighter shades mean more overfishing. EPI scores range from 1–7; 7=highest level of overfishing.

Overfishing has stripped many fisheries around the world of their

European colonisation of the Americas has been well documented.[4]

The fraction of fish stocks that are within biologically sustainable levels has exhibited a decreasing trend, from 90% in 1974 to 66.9% in 2015. In contrast, the percentage of stocks fished at biologically unsustainable levels increased from 10% in 1974 to 33.1% in 2015, with the largest increases in the late-1970s and 1980s.

Global trends in the state of the world's marine fish stocks, from FAO's Statistical Yearbook 2020[5]

In 2015, maximally sustainably fished stocks (formerly termed fully fished stocks) accounted for 59.9% and underfished stocks for 7% of the total assessed stocks.[6] While the proportion of underfished stocks decreased continuously from 1974 to 2015, the maximally sustainably fished stocks decreased from 1974 to 1989, and then increased to 59.9% in 2015.[6]

In 2015, among the 16 major statistical areas, the

Atlantic 58.8%. In contrast, the Eastern Central Pacific, Northeast Pacific (Area 67), Northwest Pacific (Area 61), Western Central Pacific and Southwest Pacific had the lowest proportion (13 to 17%) of fish stocks at biologically unsustainable levels.[6]

fisheries scientist known for pioneering work on the human impacts on global fisheries, has commented:[7]

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.

According to the Secretary General of the 2002 World Summit on Sustainable Development, "Overfishing cannot continue, the depletion of fisheries poses a major threat to the food supply of millions of people."[8]

The fishing down the food web is something that occurs when overfishing arises. Once all larger fish are caught, the fisherman will start to fish the smaller individuals, which would lead to more fish needing to be caught to keep up with demand.[9] This decreases fish populations, as well as genetic diversity of the species, making them more susceptible to disease, and less likely to adapt to their stressors and the environment.[10] Additionally, catching smaller fish leads to breeding of smaller offspring, which can be problematic for fish. In many species, the smaller the female, the less fecund it is, impacting the fish population.[11]

Types

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

Growth Overfishing

Overfishing can deplete key reef species and damage coral habitat. Coral reef fish are a significant food source for over a billion people worldwide.[12]

Growth overfishing occurs when fish are harvested at an average size that is smaller than the size that would produce the maximum yield per recruit. A recruit is an individual that makes it to maturity, or into the limits specified by a fishery, which are usually size or age.[13] This makes the total yield less than it would be if the fish were allowed to grow to an appropriate size. It can be countered by reducing fishing mortality to lower levels and increasing the average size of harvested fish to a size that will allow maximum yield per recruit.[14][15]

Recruitment Overfishing

Recruitment overfishing happens when the mature adult population (spawning biomass) is depleted to a level where it no longer has the reproductive capacity to replenish itself—there are not enough adults to produce offspring.[14] 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

Ecosystem overfishing occurs when the balance of the ecosystem is altered by overfishing. With declines in the abundance of large predatory species, the abundance of small forage type increases causing a shift in the balance of the ecosystem towards smaller fish species.

Examples and evidence for overfishing

Examples of overfishing exist in areas such as the

extractive industries such as forestry and hunting, fisheries are susceptible to economic interaction between ownership or stewardship and sustainability, otherwise known as the tragedy of the commons
.

Overfished US stocks, 2015
  • Tuna has been caught by the locals in the upper Adriatic for centuries. Increasing fishing prevented the large schools of little tunny from migrating into the Gulf of Trieste. The last major tuna catch was made in 1954 by the fishermen of Santa Croce, Contovello and Barcola.[18]
  • El Niño season[19] largely depleted the Peruvian anchovetas from its waters.[20][21] 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 four million tons.[19]
    This was a major loss to Peru's economy.
  • The
    Grand Banks, is a dramatic example of the consequences of overfishing.[23]
  • The
    Biodiversity Action Plan. The United Kingdom has created elements in this plan to attempt to restore the 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.[24]
  • Many
    deep sea fish are at risk, such as orange roughy 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 do not 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 for food. Flash freezing allows the trawlers to work for days at a time, and modern fishfinders target the fish with ease.[25]
  • Blue walleye became extinct in the Great Lakes in the 1980s. Until the middle of the 20th century, the walleye was a commercially valuable fish, with about a half million tones being landed in the period from about 1880 to the late 1950s, when the populations collapsed, apparently through a combination of overfishing, anthropogenic eutrophication, and competition with introduced rainbow smelt.
  • The World Wide Fund for Nature and the Zoological Society of London jointly issued their "Living Blue Planet Report" on 16 September 2015 which states that there was a dramatic fall of 74% in worldwide stocks of the important scombridae fish such as mackerel, tuna and bonitos between 1970 and 2010, and the global overall "population sizes of mammals, birds, reptiles, amphibians and fish fell by half on average in just 40 years."[26]
  • Limited supply due to past overfishing of the Pacific bluefin tuna has contributed to occasional astronomical prices. In January 2019, a 278 kilogram (612 pound) tuna sold for 333.6 million yen, or over US$3 million, US$4,900 per pound.[27][28]
  • Vladimir Popov
    was killed by a tiger shark in an attack which has been attributed to overfishing of the Red Sea.
  • A study in 2003 found that, as compared with 1950 levels, only a remnant (in some instances, as little as 10%) of all large ocean-fish stocks are left in the seas. These large ocean fish are the species at the top of the food chains (e.g.,
    pelagics (the open seas).[30]
  • In the United States approximately 27% of exploited fish stocks are considered overfished.[31]
  • In Tasmania, over 50% of major fisheries species, such as the eastern gemfish, the southern rock lobster, southern bulkefin tuna, jack mackerel, or trumpeter, have declined over the past 75 years due to overfishing.[32]

Consequences

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

According to a 2008 UN report, the world's fishing fleets are losing US$50 billion each year due to 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.[33]

Increased incidence of schistosomiasis in Africa has been linked to declines of fish species that eat the snails carrying the disease-causing parasites.[34]

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.[35] Both climate change and a restructuring of the ecosystem have been found to be major roles in an increase in jellyfish population in the Irish Sea in the 1990s.[36]

According to the 2019 Global Assessment Report on Biodiversity and Ecosystem Services published by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, overfishing is a primary driver of mass extinction in the world's oceans.[37] A 2021 study published in the journal Nature asserted that the "primary cause" of ocean defaunation is overfishing.[29] Other studies have shown that overfishing has reduced fish and marine mammal biomass by 60% since the 1800s,[38] and is currently driving over one-third of sharks and rays to extinction.[39]

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 (reduced rate of 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 diminish for long enough, replenishment will go into reverse and the population will decrease.)[40]
  • 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.[citation needed
    ]
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 model proposed in 2010 for predicting acceptable levels of fishing is the Harvest Control Rule (HCR),[41] which is a set of tools and protocols with which management has some direct control of harvest rates and strategies in relation to predicting stock status, and long-term maximum sustainable yields. Constant catch and constant fishing mortality are two types of simple harvest control rules.[42]

Input and output orientations

Fishing capacity
can also be defined using an input or 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.[43]

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.[clarification needed]

Reducing Overfishing

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 color convention introduces sets of rules based on predefined critical values, which can 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.[45]

  • Article 61 requires all coastal states to ensure that the maintenance of living resources in their
    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.

According to some observers, overfishing can be viewed as an example of the

property rights through, for instance, 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: 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."[46]

Another possible solution, at least for some areas, is

quotas, restricting fishers to a specific quantity 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 have time to recover and repopulate.

In order to maximise resources some countries, e.g., Bangladesh and Thailand, have improved the availability of family planning services. The resulting smaller populations have a decreased environmental footprint and reduced food needs.[47]

Controlling consumer behavior and demand is critical 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.[48]

Government Regulation

Many regulatory measures are available for controlling overfishing. These measures include

marine protected areas
.

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 from the one desired for fisheries.[49] 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.[50]
To fish sustainably, quotas need to be changed each year to account for fish population.

total allowable catch) to be harvested in a certain fishery. The decision considers carrying capacity, regeneration rates and future values. Under ITQs, members of a fishery are granted rights to a percentage of the total allowable catch that 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
.

In 2008, a large-scale study of fisheries that used ITQs compared to ones that did not provide strong evidence that ITQs can help to prevent collapses and restore fisheries that appear to be in decline.[51][52][53][54]

China bans fishing in the South China Sea for a period each year.[55]

Several countries are now effectively managing their fisheries. Examples include Iceland and New Zealand.[56] The United States has turned many of its fisheries around from being in a highly depleted state.[57]

Removal of Subsidies

Because government provided financial subsidies can make it economically viable to fish beyond biologically sustainable levels, several scientists have called for an end to

grenadiers, or sharks. These fish are usually long-lived and late maturing, and their populations take decades, even centuries to recover.[58]

Fisheries scientist

bottom trawl fleets around the world. They found that US$152 million per year are paid to deep-sea fisheries. Without these subsidies, global deep-sea fisheries would operate at a loss of US$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.[58]

"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.[58]

"Eliminating global subsidies would render these fleets economically unviable and would relieve tremendous pressure on over-fishing and vulnerable deep-sea ecosystems" – Sumaila.[58]

Over 30 billion euros in public subsidies are directed to fisheries annually.[59][60]

Minimizing Fishing Impact

Fishing techniques may be altered to minimize bycatch and reduce impacts on marine habitats. These techniques include using varied gear types depending on target species and habitat type. For example, a net with larger holes will allow undersized fish to avoid capture. A turtle excluder device (TED) allows sea turtles and other megafauna to escape from shrimp trawls. Avoiding fishing in spawning grounds may allow fish stocks to rebuild by giving adults a chance to reproduce.

World capture fisheries and aquaculture production by species group, from FAO's Statistical Yearbook 2020[5]

Aquaculture