Overfishing occurs when the stock (biomass ) of a fish species has been subjected to a rate or level of fishing mortality (usually from commercial fishing) that has reduced it below its capacity to maintain an established fishing (harvest ) yield. This yield is usually specified as the maximum sustainable yield (MSY), defined as the maximum amount of fish that can be removed from the biomass on a sustained basis while maintaining the same stock level, given the stock’s biological growth function (dynamics ). Overfishing is inherently a biological concept, although it is fundamentally tied to economic behavior because it involves fishing pressure or intensity beyond an optimum level. The model used to evaluate it is thus called a bioeconomic model.
To more specifically define overfishing it is necessary to determine what fishing level would be optimal in terms of the biological stock, or not constitute overfishing. The first step is to define the biological growth function, which is generally attributed to Milner B. Schaefer (1954; see also Anderson 1986). Given his assumption of a logistic growth equation, a sustainable yield curve can be drawn as a parabola, expressed in terms of either the biomass stock (S) or fishing effort (E), as shown on the left and right hand side of Figure 1, respectively.
In an unexploited state (no mortality from fishing) the fishery is in a biological equilibrium where growth is zero, at the left-hand extreme of both curves in the figure. If fishing then begins, defined in terms of increasing fishing effort (days, or boat/crew), the fish stock falls (a movement to the right on the horizontal axis in both panels). The biomass (fish) growth that may be harvested (caught) on a sustainable basis rises, however (as indicated by the increasing yield on the vertical axis with a move up the
curves), because the stock will be regenerating toward the biological equilibrium.
The maximum possible sustained yield is attained at the very top of the curve(s), which shows the MSY fish stock (Smsy), the effort required to harvest that stock on a sustained basis if no shock changes the curves (Emsy), and the maximum catch attainable in that state (Cmsy). If more fishing effort than Emsy is applied to harvesting, however, the stock and thus sustainable catch decline (a movement down the right hand sides of the curves), because reproduction is not proceeding fast enough to counteract the exploitation. This is a state of overfishing, represented by the lower sustained yield (or mortality) than possible (such as at C < Cmsy). The stock is thus overfished, characterized by a lower stock than at the MSY point (S < Smsy), and the fishery is overcapitalized (E > Emsy).
Overfishing is the likely outcome in an unmanaged fishery because it is common property or open access (no one owns the fish), so fishers will keep fishing as long as they find it profitable. Such overuse is generally expected for common property or common pool resources, a problem often called “the tragedy of the commons” (see Hardin 1968). That is, overexploitation of the stock occurs because without property rights fishing will continue until the average rather than marginal benefits of harvesting are equal to marginal costs. In the standard bioeconomic model this results in an effort level on the right hand side of effort curve.
A primary goal of fishing management is thus to counteract the incentive to fish the stock down to an over-exploited or overfished state. This can be accomplished by command and control polices such as limits on the total allowable catch or days at sea. Such policies still do not provide incentives for fishers to maximize the economic value of the fishery, which is best accomplished by conferring property rights on fishers to approximate a socially optimal outcome. Such programs can be difficult to implement, however, due to distributional and political issues about who is allowed to fish, how much revenue each fisher receives, and how such rights should be conferred (e.g., for free or auctioned off with the proceeds going to the public or to support fishery management).
SEE ALSO Coase Theorem; Externality; Tragedy of the Commons
Anderson, Lee. 1986. The Economics of Fisheries Management. Baltimore, MD: Johns Hopkins University Press.
Hardin, Garrett. 1968. The Tragedy of the Commons. Science 162: 1243–1248.
Schaefer, Milner B. 1954. Some Aspects of the Dynamics of Populations Important to the Management of Commercial Marine Fisheries. Bulletin of the Inter-American Tropical Tuna Commission 1: 25–56.
Catherine J. Morrison Paul
"Overfishing." International Encyclopedia of the Social Sciences. . Encyclopedia.com. (September 25, 2018). http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/overfishing
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http://www.oceanconservancy.org; http://www.nmfs.noaa.gov; http://www.panda.org
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With the tremendous increase in the human population since the industrial revolution, there has been an ever increasing use and, often, exploitation of many of the world's natural resources . The demand for fish and shellfish has exemplified this misuse of natural resources. Paralleling the changes in agriculture, the fisheries industry has progressed from a small-scale, subsistence operation to a highly mechanized, ultra-efficient means of securing huge quantities of fish and shellfish to satisfy the burgeoning market demand. These industrialized commercial fisheries have allowed fishermen to easily work the far offshore waters, and more efficient refrigeration has allowed greater travel time, thus allowing for longer excursions.
Overfishing results in the removal of a substantial portion of a species' population so that there are too few individuals left to reproduce and bring the population back to the level it was the year before. Overfishing has a tremendous negative impact on nontarget species as well. More than half, and occasionally as much as 90%, of a catch may be discarded, and this can adversely affect the environment by altering predator-prey ratios and adding excess organic waste through the dumping of nearly 30 million tons of dead or dying fish and shellfish overboard annually. Overfishing has also negatively impacted diving seabird, sea turtle, and dolphin populations since these animals often get trapped and killed in fishing nets. It is estimated that 44,000 albatrosses are killed each year by Japanese tuna fishermen, and that, over the years, tuna purse seine nets in the Eastern Tropical Pacific have caused the death of millions of dolphins .
The offshore waters are not regulated as are the coastal waters of our continents, therefore several populations of commercially important species have been overfished. Often, fishermen simply try to catch as many fish as possible (as fast as possible), because they believe that any fish left in the water will be caught by someone else. The codfish industry of the Atlantic coast of Canada and the United States had been a productive fishery since the time of the early settlers, hundreds of years ago. But with the introduction, in 1954, of a new kind of highly industrialized fishing vessel, the factory trawler, conditions changed for the cod population. In 1968, exceeding the normal catch for the region by over 500,000 tons, 810,000 tons of cod were taken off Labrador and the Grand Banks off Newfoundland. In the decade to follow, the cod population declined to the point that the number of spawning codfish off Newfoundland in 1977 showed a 94% decrease from the number in 1962. Another species to show population decline due to overfishing is the American shad, often referred to as the poor man's salmon . Harvested by Native Americans and the early colonists, the shad fishery was supplying one of the most commercially valuable fish to the region surrounding the Chesapeake Bay during the 1800's. Overfishing, combined with an increase in pollution and the disruption of spawning runs by the damming of rivers, took a fishery with an annual harvest of nearly 18 million pounds at the turn of the century to less than 2 million pounds in the 1970s.
A tragic example of the effect of overfishing is seen at Georges Bank in the Atlantic Ocean. Georges Bank, discovered by the Italian explorer Giovanni da Verrazano in the early part of the 16th century, was named after St. George by English settlers in 1605. Home to over 100 species of fish, Georges Bank has been a historically significant site of plentiful fishing for centuries. It is an ovoid embankment that is about 75 miles (120 km) off of the coast of New England. It encompasses an area 149 miles (240 km) in length and 75 miles (120 km) in width, and is over 330 feet (100 meters) above the sea floor of the adjacent Gulf of Maine. A bank, or shoal, is a shallow portion of an ocean that is analogous to a plateau. Georges Bank is part of a large range of shoals that extends from Newfoundland to the edge of the North American continental shelf. Georges Bank itself is larger than the state of New Jersey, and is an extremely important breeding ground for cod, haddo! ck, herring, flounder, lobster, and scallops. Its unique conditions are formed by the mingling of two major Atlantic currents: the cold Labrador current and the warm Gulf stream. The mixing of nutrient-rich and well-oxygenated waters in combination with good light penetration due to shallow depth creates an ideal environment for plankton that is a vital food source for young fish.
Known for its abundant fish supply, Georges Bank was heavily fished for centuries. Early fisheries believed the supply to be inexhaustible. The first documented consequence of indiscriminate fishing was in 1850 when, after a concentrated season of overfishing, a dramatic decline in halibut numbers in Georges Bank threatened commerce. The near extinction of halibut in this area occurred when ocean fishing was still accomplished using relatively small sailboats and handlines with baited hooks. After World War II, colossal factory-sized fishing ships were created and new large-scale fishing techniques were employed in Georges Bank. Miles of gill nets and other efficient methods became standard tools for trolling the bank. Fisheries from the United States, the Soviet Union, Spain, Japan, and Germany collected huge bounties from Georges Bank for decades. Each modern ship could catch as much cod in a single hour as an average boat from the 1600s could collect in an enti! re season. The fishing industry boomed from the 1950s through the 1970s, until it became apparent that even the ocean had limits that could be surpassed.
In 1976, the United States passed the Magnuson Act which established American authority to ban international factory fishing in the Georges Bank area. The intention was to protect and preserve fish stocks for the United States and Canada. Rather than initiate conservation strategies for managing the fish populations of Georges Bank, western fisheries free from foreign competition in the area, advanced. The New England Council, created by the Magnuson Act to protect Georges Bank, was effectively controlled by fishing industry interests that did little to address growing concerns about dwindling supplies.
In 1994 the National Marine Fisheries Service estimated a 40% decline in cod stocks in the Georges Bank area that occurred over an alarmingly short four-year period. Survey after survey found that the once abundant bank had been stripped of every prime commercial fish species that once filled its waters. As a result, that same year, fishing was banned in a 9,600 square kilometer area of Georges Bank. As of 1999, scientists reported that some commercial species were beginning to show signs of a slow increase in numbers, but that cod continued a rapid decline. While the ban on heavy fishing continues, some strictly regulated fishing is permitted in certain areas of Georges Bank. Although the depletion of fish populations in Georges Bank are assumed by some to be temporary, scientists remain cautious about providing assurances of a return to former abundance since recovery from such massive overfishing is not well understood.
Because regions relatively close to land, such as Georges Bank, tend to be more regulated, fishermen have begun to move farther out into unregulated water. Lack of regulations, however, is not the only reason fishermen are going farther offshore. Many populations have been over-fished in coastal waters, but fish and shellfish populations have declined in these waters due to near-shore pollution as well. Decreased water quality has had an impact on the population numbers and also on the quality of the fish itself, therefore creating a demand for fish and shellfish from distant, presumably cleaner, waters. Being driven farther offshore to make their catches, commercial fishermen may often overfish a population to bring in more revenues to offset their huge debt incurred on their equipment, crew, and ever increasing fuel costs.
A particularly alarming new method of fishing that threatens ocean fauna is cyanide fishing. Cyanide fishing is an increasingly popular method of fishing that uses cyanide to temporarily stun fish in exotic areas, like coral reefs. Once stunned, the fish are easily collected, then sold either as aquarium pets or as live fish in restaurants. Live fish sell for much higher prices than frozen fish, and live fish selections in restaurants is a growing trend. One problem with cyanide fishing is that only about half of the fish captured survive for sale, making it a wasteful effort. A second problem is the nonselective poisoning of other wildlife found in the ecosystems. Coral itself is killed by the cyanide used to flush-out exotic species from hiding places for luxury fish markets in Asia. Cyanide fishing constitutes a new threat for overfishing. It is estimated that roughly 65 tons of cyanide are used each year in Philippine coral reefs alone. Cyanide used on one! area spreads and jeopardizes ocean life on a scale that is poorly understood.
Popular trends in cuisine, in addition to live exotic fish selections in restaurants, can effect fishing. During the 1980s, when a New Orleans chef popularized "blackened redfish" and the dish was in demand across the country, the Gulf of Mexico population of "redfish", actually the Red drum, was nearly decimated by overfishing. Because of its unpopularity as a food and game fish, the Red drum was not regulated as are the more important commercial fish and shellfish species of this region. Therefore, when orders for the fish started coming in from across the nation, commercial fishermen began catching them in record numbers. There were cases in which great numbers of dead redfish were washing up on the shores of the Gulf states because fishermen had caught too many to process on their vessels and dumped the excess overboard. In just a couple of years the Red drum population crashed in the Gulf of Mexico, prompting the fish and game officials in all of the Gulf states to halt commercial fishing for redfish. (A recovery program, however, is meeting with success.) This problem could have been avoided had the original dish been named "blackened fish" or had the nation's seafood markets and restaurants known that the flavor in "blackened redfish" is in the seasonings and not in the fish itself, thus relying on local fisheries and the redfish of the Gulf of Mexico.
One means of offsetting overfishing by commercial fishing fleets, and reducing fuel use as well, is aquaculture , the cultivation and harvesting of fish and shellfish under controlled conditions. With pressures on fish populations from overfishing, increased pollution problems, and a dying industry strapped with higher costs of fuel and equipment, "fish farming" may offer a true alternative to greatly reduced quantities and inferior quality seafood in the future.
See also Commercial fishing
[Eugene Beckham ]
Bricklemyer, E., S. Iudicello, and H. Hartmann. "Discarded Catch in U.S. Commercial Marine Fisheries." Audubon Wildlife Report. San Diego: Academic Press, 1990–91.
Kunzig, Robert. 1995. Twilight of the Cod. Discover, April 1995,44–49, 52–57, 60.
Lawren, B. "Net Loss." National Wildlife 30 (1992): 46–53.
"Overfishing." Environmental Encyclopedia. . Encyclopedia.com. (September 25, 2018). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/overfishing
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Overfishing refers to a situation in which the fishing industry removes more fish than can be replaced by reproduction of the fish left in the ecosystem. Due to improvements in technology, fishing yields have grown dramatically over the last 50 years. The quantity of fish removed from the ocean by fishing probably approaches the maximum sustainable yield of the ocean. There are several examples of fisheries that have been decimated by overfishing, such as the cod fishery in the North Atlantic and the New Zealand orange roughy industry.
One of the major problems associated with the fishing industry is the high percentage of bycatch that is removed from the ocean during fishing practices. Advances in fishing technology and pressure by non-profit organizations are helping to improve fisheries management to prevent overfishing.
Historical Background and Scientific Foundations
Fish represent about 16% of the protein in the human diet and this percentage is much greater in developing countries. According to the United Nation’s Food and Agricultural Organization (FAO), in Asia, 30% of the animal protein in people’s diet comes from fish; in Africa about 20% comes from fish; and in Latin America fish contribute about 8% of the animal protein to people’s diets. More than 100 million people depend on the fishing industry for employment in developing countries alone.
Approximately 90% of all fisheries’ yield are marine fish. The most common types of commercial fish include small pelagic species like anchovies, anchovetta, sardines, and herring. Larger open ocean predators like the jacks, tunas, billfish, bonito, redfish, mackerels, and basses are also important to commercial fisheries. Other fished species include swimming invertebrates such as krill, shrimp, crab, lobster, oyster, scallop, octopus, and squid. Marine algae including Ulva, Poryphyra and Laminaria account for roughly 3% of the marine fisheries.
The quantity of fish caught by fishermen has increased rapidly over the last five decades. Since 1950 the annual fish yield increased from 21 million tons to around 90 million tons. The Peruvian anchoveta is the most caught marine species, with a yield of around 10 million tons. China catches the most fish worldwide, with an annual yield approaching 17 million tons.
The great growth in the fishing yield is a result of several factors. Most fish are caught by commercial fishermen from large fleets of ships. The technology employed by these fishing businesses is vast, including satellite sensors, sonar tracking, scouting ships, and spotting airplanes. Enormous factory ships act as entire processing facilities with spaces for cleaning, canning, and freezing all on board. These great fleets of ships have been able to exploit fishing grounds that were largely inaccessible in the past, particularly in the Southern Hemisphere.
Even with the immense fishing effort, the yield of fish taken from the ocean has leveled off, and even declined since the 1980s. Fisheries experts estimate that the maximum sustainable yield that can be removed from the oceans is somewhere near 110 to 150 million tons. The current yield is extremely close to the lower end of this estimate. When so many fish are taken from the ocean that the remaining fish cannot replenish those removed by breeding, the condition is known as over-fishing.
In 2006, the FAO’s report on the state of the world’s fisheries showed that almost 80% of the fisheries were threatened by overfishing. More than 25% of the world’s fish stocks were overexploited or depleted. More than half of the total fish stocks were exploited. The report estimates that at least 90% of the world’s largest predatory fish, like the oldest tuna and swordfish, are no longer in existence.
One of the most dramatic examples of overfishing occurred in Newfoundland, Canada. The cod fishery had thrived in the region for hundreds of years. However, years of overfishing driven by poor management practices depleted the standing stocks so greatly that the entire fishery collapsed in one year. In 1992, more than 35,000 people lost their jobs when the cod did not return at the beginning of the fishing season. The fishery, and the region’s economy, are still in a state of disrepair.
Other examples of similar fisheries crashes as a result of overfishing exist. Orange roughy from waters near New Zealand became extremely popular in the 1980’s for its mild, delicate flavor. The fish grows extremely slowly and can live as old as 100 years. It is not able to reproduce until it is 25 to 30 years old. As fishing pressure removed the older, larger fish, the remaining orange roughy were too young to reproduce. After only 13 years of fishing for orange roughy, the species was nearly extinct.
Impacts and Issues
Management of the fisheries industries has the goal of preventing overfishing. The objectives are to maximize the yield of fish, while at the same time maximizing the economic yield. This has led to poor decisions that deplete standing stocks of fish and disrupt ecosystems that sustain commercial fish populations. When fish catch drops, management practices often increase the number of fishing licenses and the number of boats allowed in the fishing fleet. Some organizations estimate that there are currently 2 to 3 times the number of vessels fishing the oceans than are required to catch the maximum yield. In order to support these fishing efforts the governments of the United States, Japan, the European Union, and Russia all subsidize fishing fleets, which significantly exacerbates overfishing.
One of the most notable problems contributing to the depletion of fisheries stocks in the ocean a known as bycatch or bykill. Bycatch refers to the collection of non-target species by fishermen. Most often bycatch is removed from the catch and thrown overboard back into the ocean, where, presumably, it dies. Bycatch has enormous ramifications. Approximately 20 million tons of fish food are lost to bycatch per year. It is estimated that the tuna fisheries kill one million sharks a year. In the shrimp industry, approximately 80% of the catch is bycatch. Bycatch is not restricted to fish; marine mammals, birds, and turtles are all killed as bycatch.
Advances in fishing technology can significantly reduce bycatch. Circle hooks are specially designed to catch the species of fish that fishermen can sell in mar-
WORDS TO KNOW
AQUACULTURE: The farming of fish or shellfish in freshwater or saltwater.
BYCATCH: Non-target species killed in the process of fishing.
SUSTAINABILITY: Practices that preserve the balance between human needs and the environment, as well as between current and future human requirements.
kets. Specially shaped nets exclude species that will otherwise become bycatch. Harpooning large species with spot planes, rather than using long lines or drift nets, also significantly decreases bycatch. Finally, producing fish in aquaculture farms brings fish to market, without creating bycatch.
Government oversight of fishing is often inconsistent and poorly regulated. There are few international regulations that control fishing in the open ocean. Exclusive Economic Zones (EEZs) are waters within 200 mi (321 km) of a country’s coastline. Within these strips of ocean, governments can regulate fishing. However 64% of the ocean falls outside these regions and international laws are few and poorly enforced.
Since the fishing industry is market driven, some non-profit organizations have begun publishing seafood guides to urge consumers to make careful choices about the types of fish that they eat. By discouraging consumption of fish that are caught with significant bycatch or in poorly managed fisheries, these organizations hope to influence the industry and its managers to make better decisions about sustaining fisheries. In particular, Monterey Bay Aquarium has developed a Seafood Watch program that helps businesses and consumers make choices for healthy oceans. One of the major successes has been the publication and distribution of pocket guides recommending consumers buy sustainable species of fish when they are shopping.
Other groups have put pressure on fish sellers to identify the source of the seafood they sell as well as the methods used to harvest it. For example, the grocery chain Whole Foods Market is committed to only selling fish from well-managed fisheries. The Marine Stewardship Council (MSC) is a British organization that identifies and certifies sustainable fisheries.
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"Overfishing." Environmental Science: In Context. . Encyclopedia.com. (September 25, 2018). http://www.encyclopedia.com/environment/energy-government-and-defense-magazines/overfishing
"Overfishing." Environmental Science: In Context. . Retrieved September 25, 2018 from Encyclopedia.com: http://www.encyclopedia.com/environment/energy-government-and-defense-magazines/overfishing