Overexploitation
Overexploitation, also called overharvesting, refers to harvesting a
In
Overexploitation can lead to resource destruction, including
History
Concern about overexploitation is relatively recent, though overexploitation itself is not a new phenomenon. It has been observed for millennia. For example, ceremonial cloaks worn by the Hawaiian kings were made from the mamo bird; a single cloak used the feathers of 70,000 birds of this now-extinct species. The dodo, a flightless bird from Mauritius, is another well-known example of overexploitation. As with many island species, it was naive about certain predators, allowing humans to approach and kill it with ease.[7]
From the earliest of times,
In more recent times, overexploitation has resulted in the gradual emergence of the concepts of
Overview
Overexploitation does not necessarily lead to the destruction of the resource, nor is it necessarily unsustainable. However,
Tragedy of the commons
In 1968, the journal Science published an article by Garrett Hardin entitled "The Tragedy of the Commons".[14] It was based on a parable that William Forster Lloyd published in 1833 to explain how individuals innocently acting in their own self interest can overexploit, and destroy, a resource that they all share.[15][pages needed] Lloyd described a simplified hypothetical situation based on medieval land tenure in Europe. Herders share common land on which they are each entitled to graze their cows. In Hardin's article, it is in each herder's individual interest to graze each new cow that the herder acquires on the common land, even if the carrying capacity of the common is exceeded, which damages the common for all the herders. The self-interested herder receives all of the benefits of having the additional cow, while all the herders share the damage to the common. However, all herders reach the same rational decision to buy additional cows and graze them on the common, which eventually destroys the common. Hardin concludes:
Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit—in a world that is limited. Ruin is the destination toward which all men rush, each pursuing his own interest in a society that believes in the freedom of the commons. Freedom in a commons brings ruin to all.[14]: 1244
In the course of his essay, Hardin develops the theme, drawing in many examples of latter day commons, such as national parks, the atmosphere, oceans, rivers and fish stocks. The example of fish stocks had led some to call this the "tragedy of the fishers".[16] A major theme running through the essay is the growth of human populations, with the Earth's finite resources being the general common.
The tragedy of the commons has intellectual roots tracing back to
The tragedy of the commons can be avoided if it is appropriately regulated. Hardin's use of "commons" has frequently been misunderstood, leading Hardin to later remark that he should have titled his work "The tragedy of the unregulated commons".[19]
Sectors
Fisheries
In wild fisheries, overexploitation or overfishing occurs when a fish stock has been fished down "below the size that, on average, would support the long-term maximum sustainable yield of the fishery".[20] However, overexploitation can be sustainable.[21]
When a fishery starts harvesting fish from a previously unexploited stock, the biomass of the fish stock will decrease, since harvesting means fish are being removed. For sustainability, the rate at which the fish replenish biomass through reproduction must balance the rate at which the fish are being harvested. If the harvest rate is increased, then the stock biomass will further decrease. At a certain point, the maximum harvest yield that can be sustained will be reached, and further attempts to increase the harvest rate will result in the collapse of the fishery. This point is called the maximum sustainable yield, and in practice, usually occurs when the fishery has been fished down to about 30% of the biomass it had before harvesting started.[22]
It is possible to fish the stock down further to, say, 15% of the pre-harvest biomass, and then adjust the harvest rate so the biomass remains at that level. In this case, the fishery is sustainable, but is now overexploited, because the stock has been run down to the point where the sustainable yield is less than it could be.
Fish stocks are said to "collapse" if their biomass declines by more than 95 percent of their maximum historical biomass. Atlantic cod stocks were severely overexploited in the 1970s and 1980s, leading to their abrupt collapse in 1992.[1] Even though fishing has ceased, the cod stocks have failed to recover.[1] The absence of cod as the apex predator in many areas has led to trophic cascades.[1]
About 25% of world fisheries are now overexploited to the point where their current biomass is less than the level that maximizes their sustainable yield.[23] These depleted fisheries can often recover if fishing pressure is reduced until the stock biomass returns to the optimal biomass. At this point, harvesting can be resumed near the maximum sustainable yield.[24]
The
Water resources
Water resources, such as lakes and aquifers, are usually renewable resources which naturally recharge (the term fossil water is sometimes used to describe aquifers which do not recharge). Overexploitation occurs if a water resource, such as the Ogallala Aquifer, is mined or extracted at a rate that exceeds the recharge rate, that is, at a rate that exceeds the practical sustained yield. Recharge usually comes from area streams, rivers and lakes. An aquifer which has been overexploited is said to be overdrafted or depleted. Forests enhance the recharge of aquifers in some locales, although generally forests are a major source of aquifer depletion.[27][28] Depleted aquifers can become polluted with contaminants such as nitrates, or permanently damaged through subsidence or through saline intrusion from the ocean.
This turns much of the world's underground water and lakes into finite resources with peak usage debates similar to
Forestry
Forests are overexploited when they are logged at a rate faster than reforestation takes place. Reforestation competes with other land uses such as food production, livestock grazing, and living space for further economic growth. Historically utilization of forest products, including timber and fuel wood, have played a key role in human societies, comparable to the roles of water and cultivable land. Today, developed countries continue to utilize timber for building houses, and wood pulp for paper. In developing countries almost three billion people rely on wood for heating and cooking.[33] Short-term economic gains made by conversion of forest to agriculture, or overexploitation of wood products, typically leads to loss of long-term income and long term biological productivity. West Africa, Madagascar, Southeast Asia and many other regions have experienced lower revenue because of overexploitation and the consequent declining timber harvests.[34]
Biodiversity
Overexploitation is one of the main threats to global biodiversity.[3] Other threats include pollution, introduced and invasive species, habitat fragmentation, habitat destruction,[3] uncontrolled hybridization,[35] climate change,[36] ocean acidification[37] and the driver behind many of these, human overpopulation.[38]
One of the key health issues associated with biodiversity is drug discovery and the availability of medicinal resources.[39] A significant proportion of drugs are natural products derived, directly or indirectly, from biological sources. Marine ecosystems are of particular interest in this regard.[40] However, unregulated and inappropriate bioprospecting could potentially lead to overexploitation, ecosystem degradation and loss of biodiversity.[41][42][43]
Endangered and extinct species
Species from all groups of fauna and flora are affected by overexploitation.
All living organisms require resources to survive. Overexploitation of these resources for protracted periods can deplete natural stocks to the point where they are unable to recover within a short time frame. Humans have always harvested food and other resources they have needed to survive. Human populations, historically, were small, and methods of collection limited to small quantities. With an exponential increase in
This is more prevalent when looking at island ecology and the species that inhabit them, as islands can be viewed as the world in miniature. Island endemic populations are more prone to extinction from overexploitation, as they often exist at low densities with reduced reproductive rates.[46] A good example of this are island snails, such as the Hawaiian Achatinella and the French Polynesian Partula. Achatinelline snails have 15 species listed as extinct and 24 critically endangered[47] while 60 species of partulidae are considered extinct with 14 listed as critically endangered.[48] The WCMC have attributed over-collecting and very low lifetime fecundity for the extreme vulnerability exhibited among these species.[49]
As another example, when the humble
Where there is substantial human migration, civil unrest, or war, controls may no longer exist. With civil unrest, for example in the
Vertebrates
Overexploitation threatens one-third of endangered
Birds
Overall, 50 bird species that have become extinct since 1500 (approximately 40% of the total) have been subject to overexploitation,[55] including:
- feathers, meat, fat and oil.
- crop protectionand its feathers.
Mammals
- The international trade in fur: chinchilla, vicuña, giant otter and numerous cat species
Fish
Various
Invertebrates
- butterflies
- molluscs
Plants
- cactiand many other plant species
Cascade effects
Overexploitation of species can result in knock-on or
A classic example of cascade effects occurred with
One of the sea otters’ primary food sources is the
In 1911, when only one small group of 32 sea otters survived in a remote cove, an international treaty was signed to prevent further exploitation of the sea otters. Under heavy protection, the otters multiplied and repopulated the depleted areas, which slowly recovered. More recently, with declining numbers of fish stocks, again due to overexploitation,
See also
- Carrying capacity
- Common-pool resource
- Conservation biology
- Defaunation
- Deforestation
- Ecosystem management
- Exploitation of natural resources
- Extinction
- Human overpopulation
- Inverse commons
- Over-consumption
- Overpopulation in wild animals
- Paradox of enrichment
- Planetary boundaries
- Social dilemma
- Sustainability
- Tyranny of small decisions
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Further reading
- ISBN 978-92-5-105449-9
- We’ve overexploited the planet, now we need to change if we’re to survive. Patrick Vallance for The Guardian. July 8, 2022.