Overfishing happens when fish and other aquatic animals are caught from water bodies faster than they can reproduce and grow back. This leads to fewer fish in those areas over time. Overfishing can occur in any water environment, such as ponds, rivers, lakes, and oceans. It can cause fish populations to shrink, slow down the growth of species, and reduce the total number of fish. If overfishing continues, especially through large-scale fishing operations, fish populations may not be able to survive, leading to local extinction or even complete extinction. For example, overfishing sharks has disrupted entire ocean ecosystems. Types of overfishing include catching fish before they grow large enough, catching young fish before they can reproduce, and harming ecosystems by removing too many species. Overfishing harms biodiversity and ecosystems, and it also reduces the number of fish available for people to use, which can cause problems for communities and economies.

A fishery’s ability to recover from overfishing depends on whether the environment can support fish returning. When some fish species disappear, other species may take their place, changing how the ecosystem functions. For example, if trout are overfished, carp might become more common, making it hard for trout to return.

Since the 1950s, fishing has expanded to nearly all areas of the world’s oceans. Practices like dragging fishing nets across the ocean floor damage coral, sponges, and other slow-growing sea life that provide homes for fish. This harms ecosystems and can permanently change what species live in an area. Bycatch, which is the accidental catching of animals not targeted by fishermen, is common. Many of these animals are released back into the ocean but often die from injuries or exposure. Bycatch makes up about one-fourth of all marine catches. For example, when catching shrimp, the amount of bycatch is five times the amount of shrimp caught.

A 2020 report by the Food and Agriculture Organization (FAO) stated that in 2017, 34% of the world’s marine fish stocks were overfished. Ways to reduce overfishing include government rules, ending harmful fishing subsidies, reducing the impact of fishing, using aquaculture (raising fish in controlled environments), and increasing public awareness about sustainable fishing.

Scale

Overfishing has caused many fish populations around the world to decrease. A report from the United Nations Food and Agriculture Organization in 2018 said that 33.1% of fish populations are being overfished. Overfishing has also been a problem for a long time, even before the industrial era. For example, overfishing in the western Atlantic Ocean began when Europeans first settled in the Americas and is well recorded in history.

The number of fish populations that are being fished at levels that allow them to stay healthy has decreased over time. In 1974, 90% of fish populations were fished at sustainable levels, but by 2015, this number dropped to 66.9%. At the same time, the percentage of fish populations being fished in ways that harm their health increased from 10% in 1974 to 33.1% in 2015. This increase was most noticeable in the late 1970s and 1980s.

In 2015, 59.9% of fish populations were fished in the most sustainable way, and 7% were fished at levels that were too low. The number of underfished populations has steadily decreased since 1974. However, the number of populations fished in the most sustainable way first decreased from 1974 to 1989, then increased to 59.9% by 2015.

In 2015, among the 16 major regions studied, the Mediterranean and Black Sea had the highest percentage (62.2%) of fish populations being fished unsustainably. The Southeast Pacific (61.5%) and Southwest Atlantic (58.8%) followed closely. In contrast, the Eastern Central Pacific, Northeast Pacific (Area 67), Northwest Pacific (Area 61), Western Central Pacific, and Southwest Pacific had the lowest percentages (13 to 17%) of fish populations being fished unsustainably.

Daniel Pauly, a scientist who studies how humans affect global fisheries, has said:

According to the Secretary General of the 2002 World Summit on Sustainable Development, "Overfishing cannot continue, because the loss of fish populations threatens the food supply for millions of people."

Fishing down the food web happens when overfishing occurs. When larger fish are caught, fishermen begin catching smaller fish instead. This means more fish must be caught to meet demand, which reduces fish populations and the genetic diversity of species. This makes fish more likely to get sick and less able to adapt to challenges and changes in their environment. Catching smaller fish also causes smaller offspring to be born. In many species, smaller females produce fewer offspring, which harms the overall fish population.

Types

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

Growth overfishing happens when fish are caught before they reach the size that would allow the most fish to be caught from each mature fish. A recruit is a fish that has grown to a certain size or age set by fishing rules. Catching fish too early reduces the total number of fish that can be caught over time. This can be fixed by reducing how much fishing happens and allowing fish to grow larger so more fish can be caught in the future.

Recruitment overfishing occurs when the number of adult fish that can reproduce is reduced to a point where there are not enough adults to produce enough young fish. To fix this, managers aim to increase the number of adult fish to a safe level. This is usually done by banning fishing, setting limits on how many fish can be caught, or requiring fish to be a certain size before they can be caught.

Ecosystem overfishing happens when overfishing changes the natural balance of the ocean. When large predatory fish are removed, smaller fish that are usually eaten by these predators increase in number. This causes the ecosystem to shift toward having more small fish and fewer large ones.

Examples and evidence for overfishing

Overfishing has occurred in areas such as the North Sea, the Grand Banks of Newfoundland, and the East China Sea. In these places, overfishing has harmed fish populations and the communities that depend on fishing for their livelihoods. Like other industries that take resources from nature, such as logging and hunting, fisheries face challenges related to how people manage shared resources, a situation called the "tragedy of the commons."

Tuna has been caught in the upper Adriatic Sea for many years. Increased fishing activity stopped large groups of little tunny from moving into the Gulf of Trieste. The last major tuna catch in this area happened in 1954 by fishermen from Santa Croce, Contovello, and Barcola.

In the 1970s, overfishing and an El Niño event caused the Peruvian anchovy fishery to collapse. Anchovies were a key natural resource in Peru, with 10.2 million metric tons caught in 1971 alone. However, the next five years saw only about 4 million tons caught, causing major economic harm to Peru.

The collapse of the Atlantic northwest cod fishery near Newfoundland and the 1992 decision by Canada to stop fishing on the Grand Banks is a clear example of the effects of overfishing.

Sole fisheries in the Irish Sea, the west English Channel, and other areas have been overfished to the point of near collapse, according to the UK government's Biodiversity Action Plan. The UK has taken steps to restore these fisheries, but growing global demand for fish threatens their stability and the survival of the species.

Many deep-sea fish, such as orange roughy, rattails, sharks, and sablefish, are at risk. These fish grow slowly, reproduce slowly, and take 30 to 40 years to reach maturity. A single fillet of orange roughy could be 50 years old. Most deep-sea fish live in international waters with no legal protections and are caught by deep trawlers near underwater mountains. Modern technology allows trawlers to find and catch these fish easily.

Blue walleye became extinct in the Great Lakes in the 1980s. Before the mid-20th century, walleye was a valuable commercial fish, with about half a million tonnes caught between 1880 and the late 1950s. Populations then declined due to overfishing, pollution from human activities, and competition with non-native rainbow smelt.

In 2015, the World Wide Fund for Nature and the Zoological Society of London reported that global stocks of scombridae fish, such as mackerel, tuna, and bonitos, dropped by 74% between 1970 and 2010. Also, the average population sizes of mammals, birds, reptiles, amphibians, and fish worldwide fell by half in 40 years.

Overfishing has reduced the supply of Pacific bluefin tuna, leading to very high prices. In January 2019, a 278-kilogram tuna sold for over 3 million U.S. dollars.

Sharks and rays have declined by 71% globally since 1970 due to increased fishing pressure. Three-quarters of shark and ray species are now at risk of extinction. In 2023, a man in Egypt was killed by a tiger shark, an event linked to overfishing in the Red Sea.

A 2003 study found that only about 10% of large ocean fish stocks remain compared to 1950 levels. These large fish, such as tuna and cod, are at the top of food chains. However, this study has been criticized, and many scientists now say its results are not reliable for certain species.

In the United States, about 27% of fish stocks are overfished. In Tasmania, over 50% of major fish species, including eastern gemfish, southern rock lobster, and southern bulkefin tuna, have declined over the past 75 years due to overfishing.

Consequences

Overfishing harms biodiversity and ecosystems, and it also reduces the amount of fish that can be caught. This leads to problems for people and economies. A 2008 report by the United Nations said that fishing fleets worldwide lose about $50 billion each year because fish populations have dropped and fisheries are not managed well. The report, created by the World Bank and the UN Food and Agriculture Organization, said that half of the world’s fishing boats could be removed without changing how much fish is caught. Also, the total weight of fish in the ocean has decreased so much that it is no longer possible to catch the same amount of fish as before.

More cases of schistosomiasis in Africa are connected to fewer fish that eat the snails carrying the parasites that cause the disease.

Jellyfish populations have grown a lot, which harms fish. Jellyfish compete with fish for food, eat fish eggs, and can harm or crowd fish. They also survive in areas with little oxygen, where fish cannot live. This causes serious problems for fishing businesses. Overfishing removes a major predator of jellyfish, making their numbers grow even faster. Changes in the environment and climate have also contributed to more jellyfish in the Irish Sea during the 1990s.

A 2019 report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services said that overfishing is a main cause of the loss of ocean life. A 2021 study in the journal Nature said that overfishing is the main reason for the loss of animals in the ocean. Other research shows that fish and marine mammal populations have dropped by 60% since the 1800s. Overfishing is now causing more than one-third of sharks and rays to go extinct.

Acceptable levels

The idea of overfishing depends on what is considered an "acceptable level" of fishing. Scientists use specific terms to describe this:

• Biological overfishing happens when fishing removes fish from the ocean so quickly that the fish population cannot grow as fast as it should. This is shown in the red area of the figure. When too many fish are caught, the number of new fish born each year is not enough to replace those that are taken. Over time, the population may even shrink.

• Economic or bioeconomic overfishing also considers the cost of fishing. In this case, a fishery is overfished when the number of fish caught is more than the amount that would give the best possible profit. If fish are removed too quickly, the fishery becomes less profitable. Another way to define this is by looking at the total value of the fishery over time, using a method that compares the value of catching fish now versus later.

A model created in 2010 to help set acceptable fishing levels is called the Harvest Control Rule (HCR). This is a system of tools and rules that help manage fishing by controlling how many fish are caught and how fishing strategies are used. It helps predict how fish populations will change and how much fish can be caught long-term without harming the population. Two simple examples of HCR are constant catch, which keeps the same number of fish caught each year, and constant fishing mortality, which keeps the same rate of fishing.

Fishing capacity can also be explained in two ways:

• Input-oriented fishing capacity refers to the maximum amount of equipment and resources (like boats and nets) that can be used in a fishery, assuming all resources are used efficiently given the current conditions.

• Output-oriented fishing capacity refers to the maximum number of fish that a boat or group of boats (fleet) can catch if all resources are used fully. This depends on the number of fish available, the tools used, the age of the fish, and the technology available.

For a fishery to reach its maximum catch, each boat must operate as efficiently as possible. The level of efficiency is measured by comparing the actual number of fish caught (or resources used) to the maximum possible number of fish that could be caught (or resources that could be used) under ideal conditions.

Reducing overfishing

To address the problem of overfishing, many countries use a precautionary approach and Harvest Control Rules (HCR) to manage their fisheries. The Traffic Light system uses colors like red, yellow, and green to set fishing limits based on specific numbers. These rules can be updated as more information becomes available.

The United Nations Convention on the Law of the Sea (UNCLOS) includes rules about overfishing in Articles 61, 62, and 65.

• Article 61 requires countries with coastlines to protect fish populations in their exclusive economic zones. This includes keeping fish numbers high enough to ensure they can reproduce safely.
• Article 62 says these countries should aim to use fish resources wisely without harming the goals of Article 61.
• Article 65 allows countries to stop, limit, or control the hunting of marine mammals, such as whales and seals.

Some experts say overfishing is an example of the "tragedy of the commons," where shared resources are overused. Solutions include giving people ownership rights through privatization or fish farming. Research on the British Columbia halibut fishery shows that privatization can help protect fish stocks, improve safety, and reduce the need for resources to catch the same amount of fish.

Another solution is setting quotas, which limit how much fish can be caught. Some areas may also become "no-go zones," where fishing is not allowed to let fish populations recover.

To manage resources better, some countries, like Bangladesh and Thailand, have improved access to family planning services. This has helped reduce population growth, which lowers the demand for food and lessens environmental pressure.

Controlling what people buy and eat is important for reducing overfishing. Many programs now help consumers choose seafood that is sustainably caught. One example is the "Guide to Good Fish Guides," which lists resources to help people make informed choices.

Many rules help manage overfishing, such as fishing quotas, limits on how many fish a person can keep, licenses, closed seasons, size limits for fish, and creating marine reserves where fishing is not allowed.

A study showed that closing an area to fishing without catch limits, like individual transferable quotas (ITQs), can lead to short-term increases in fish catches but long-term harm to fish populations. This means that closing areas or creating protected zones is not effective unless paired with ITQs. Fish populations change each year, so quotas must be adjusted yearly to match these changes.

ITQs are permits that allow fishers to catch a certain amount of fish. These permits can be sold, traded, or rented. ITQs are used in countries like New Zealand, Australia, Iceland, Canada, and the United States. A study in 2008 found that fisheries using ITQs were less likely to collapse and more likely to recover.

China bans fishing in the South China Sea for part of the year to protect fish populations.

Some countries, like Iceland and New Zealand, manage their fisheries well. The United States has also improved its fisheries after they were heavily overfished.

Government subsidies can make it cheaper to fish beyond what is sustainable. Scientists suggest ending these subsidies for deep-sea fisheries. Studies show that $152 million is spent yearly on subsidies for deep-sea fishing. Without these funds, these fisheries would lose $50 million annually. Much of this money pays for fuel needed to fish far from shore.

Over $30 billion in public money is given to fisheries each year.

Fishing methods can be changed to reduce harm to fish and their habitats. For example, using nets with bigger holes lets smaller fish escape, and devices like turtle excluders help sea turtles avoid being caught in shrimp nets. Avoiding fishing in areas where fish reproduce can help their populations grow.

Aquaculture, or fish farming, allows people to raise fish in captivity. This can help protect fish stocks and reduce environmental harm. However, farming carnivorous fish like salmon often requires feeding them fishmeal and fish oil from wild fish. Salmon are easier to farm, and aquaculture has been practiced for over 150 years. Releasing farmed salmon into the wild can sometimes increase pressure on wild salmon populations.

Aquaculture became more common in the 1970s and now provides about half of all seafood harvested. Aquaculture production continues to grow while wild fishing remains steady.

Fish farming can include raising fish from birth to adulthood in captivity. Some fish are hard to breed in captivity and are caught as young fish to grow in farms. Advances in science have made it easier to breed more species in captivity, such as southern bluefin tuna, which were first bred in captivity in 2009.

As people learn more about overfishing and ocean damage, some groups encourage people to stop eating seafood or only eat seafood that is sustainably caught.

Barriers to reducing overfishing

When fish are available to everyone, such as in open-access fisheries, there is no system to stop people from taking more than their fair share. This causes competition among fishermen, who try to catch as much as possible. This situation, called the "tragedy of the commons," leads to increased costs for fishermen until their expenses equal their earnings, leaving no profit. The problem of overfishing often comes from how fishing rights are managed. Gordon showed that in fisheries where no one owns the fish, overfishing and loss of profit happen frequently.

The fishing industry often resists rules that protect fish populations because these rules can reduce their profits. Recreational fishermen also want to keep fishing freely, which leads to strong efforts to influence government decisions. These efforts can stop or weaken laws meant to prevent overfishing.

Fish move easily between different areas, making it hard to protect them in one place. A country’s efforts to conserve fish might be ignored by others. The tragedy of the commons can also lead to governments giving more money to fishing industries, which worsens the problem.

Governments can create rules to control fishing, but illegal fishing still happens. It is estimated that between 11 to 26 million tons of fish are caught illegally each year, which is 14–33% of the world’s reported catch. Illegal fishing includes actions like not reporting catches, catching the wrong type of fish, or breaking rules about how much or when fish can be caught. In some countries, poor people depend on fishing, making it hard to stop overfishing. Even in places with rules, small-scale and recreational fishermen may break them. Surveillance of illegal fishing is also a major challenge. In 2001, the United Nations Food and Agriculture Organization created the International Plan of Action to stop illegal, unreported, and unregulated fishing. This plan helps port countries inspect and report illegal fishing activities. Some illegal fishing is done on a large scale.

In areas where countries are fighting over control, such as during the "cod wars" between Britain and Iceland, overfishing may be encouraged. Outside of countries’ exclusive economic zones, where fishing is not controlled, large fishing boats can take fish freely. China is said to have the largest fishing fleet in international waters.

Many fishing areas far from land are not profitable and only stay open because of government support.