A wild fishery is a natural body of water with a sizeable free-ranging fish or other aquatic animal (crustaceans and molluscs) population that can be harvested for its commercial value. Wild fisheries can be marine (saltwater) or lacustrine/riverine (freshwater), and rely heavily on the carrying capacity of the local aquatic ecosystem.
Wild fisheries are sometimes called capture fisheries. The aquatic life they support is not artificially controlled in any meaningful way and needs to be "captured" or fished. Wild fisheries exist primarily in the oceans, and particularly around coasts and continental shelves, but also exist in lakes and rivers. Issues with wild fisheries are overfishing and pollution. Significant wild fisheries have collapsed or are in danger of collapsing, due to overfishing and pollution. Overall, production from the world's wild fisheries has levelled out, and may be starting to decline.
As a contrast to wild fisheries, farmed fisheries can operate in sheltered coastal waters, in rivers, lakes and ponds, or in enclosed bodies of water such as pools or fish tanks. Farmed fisheries are technological in nature, and revolve around developments in aquaculture. Farmed fisheries are expanding, and Chinese aquaculture in particular is making many advances. Nevertheless, the majority of fish consumed by humans continues to be sourced from wild fisheries. As of the early 21st century, fish is humanity's only significant wild food source.
See main article: World fish production.
See also: Fishing by country.
According to the Food and Agriculture Organization (FAO), the world harvest by commercial fisheries in 2010 consisted of 88.6 million tonnes of aquatic animals captured in wild fisheries, plus another 0.9 million tons of aquatic plants (seaweed etc.). This can be contrasted with 59.9 million tonnes produced in fish farms, plus another 19.0 million tons of aquatic plants harvested in aquaculture.
| Primary biomass | ||||||
|---|---|---|---|---|---|---|
Global primary production can be estimated from satellite observations. Satellites scan the normalised difference vegetation index (NDVI) over terrestrial habitats, and scan sea-surface chlorophyll levels over oceans. This results in 56.4 billion tonnes C/yr (53.8%), for terrestrial primary production, and 48.5 billion tonnes C/yr for oceanic primary production.[4] Thus, the total photoautotrophic primary production for the Earth is about 104.9 billion tonnes C/yr. This translates to about 426 gC/m²/yr for land production (excluding areas with permanent ice cover), and 140 gC/m²/yr for the oceans. However, there is a much more significant difference in standing stocks - while accounting for almost half of total annual production, oceanic autotrophs account for only about 0.2% of the total biomass. The most successful animal species, in terms of biomass, is probably the Antarctic krill, Euphausia superba, with a biomass of about 500 million tonnes.[5] However, as a group, the small aquatic crustaceans called copepods form the largest animal biomass on earth.[6] | ||||||
| Biome Ecosystem Type | Area | Mean Net Primary Production | World Primary Production | Mean biomass | World biomass | Minimum replacement rate |
| (million km²) | (gram dryC / m² / year) | (billion tonnes / year) | (kg dryC / m²) | (billion tonnes) | (years) | |
| Open ocean | 332.00 | 125.00 | 41.50 | 0.003 | 1.00 | 0.02 |
| Upwelling zones | 0.40 | 500.00 | 0.20 | 0.02 | 0.01 | 0.04 |
| Continental shelf | 26.60 | 360.00 | 9.58 | 0.01 | 0.27 | 0.03 |
| Algal beds and reefs | 0.60 | 2,500.00 | 1.50 | 2.00 | 1.20 | 0.80 |
| Estuaries & mangroves | 1.40 | 1,500.00 | 2.10 | 1.00 | 1.40 | 0.67 |
| Total marine | 361.00 | 152.01 | 54.88 | 0.01 | 3.87 | 0.07 |
| Lakes and streams | 2.00 | 250.00 | 0.50 | 0.02 | 0.04 | 0.08 |
| Terrestrial | 147.00 | 554.51 | 114.90 | 12.55 | 1,873.38 | 16.15 |
| Grand total | 510.00 | 333.87 | 170.28 | 3.68 | 1,877.29 | 11.02 |
| Source: Book: Whittaker, R. H. . Robert Whittaker (ecologist) . Likens, G. E. . Gene Likens . The Biosphere and Man . 305–328 . Leith, H . Whittaker, R H . Primary Productivity of the Biosphere . Springer-Verlag . 978-0-387-07083-4 . 1975 . https://archive.org/details/primaryproductiv0000liet/page/305 . ; Ecological Studies Vol 14 (Berlin)Darci and Taylre are biomass specialists. |
| Aquatic habitats have been classified into marine and freshwater ecoregions by the Worldwide Fund for Nature (WWF). An ecoregion is defined as a "relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species, dynamics, and environmental conditions (Dinerstein et al. 1995, TNC 1997).[7] |
| In the deep ocean, much of the ocean floor is a flat, featureless underwater desert called the abyssal plain. Many pelagic fish migrate across these plains in search of spawning or different feeding grounds. Smaller migratory fish are followed by larger predator fish and can provide rich, if temporary, fishing grounds. |
See also: Predator fish, Forage fish, Pelagic fish, Demersal fish, Coral reef fish and Coastal fish.
See also: Lentic ecosystems. Worldwide, freshwater lakes have an area of 1.5 million square kilometres.[39] Saline inland seas add another 1.0 million square kilometres.[40] There are 28 freshwater lakes with an area greater than 5,000 square kilometres, totalling 1.18 million square kilometres or 79 percent of the total.[41]
Freshwater fisheries are essential to supporting human life around the globe whether they are used for recreation or commercial use. Climate change presents several challenges in sustaining these fisheries as waters become warmer resulting in decreased dissolved oxygen, as the toxicity of pollutants increases, and as the physiological changes in fishes and changes in their habitat systems alter what we are used to. Deoxygenation and eutrophication are two major effects that are detrimental to fish and ecosystem health and the problem is more prevalent as the size of the body of water decreases.[42] Details on the changes occurring in fish physiology and their habitats can be found at the respective citation.
Increased management and surveillance on freshwater fisheries will be vital to the longevity, sustainability, and productivity of the fisheries and essential to maintaining our food production from that source.
See also: Lotic ecosystems.
See main article: Marine pollution. Pollution is the introduction of contaminants into an environment. Wild fisheries flourish in oceans, lakes, and rivers, and the introduction of contaminants is an issue of concern, especially as regards plastics, pesticides, heavy metals, and other industrial and agricultural pollutants which do not disintegrate rapidly in the environment. Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into the sea. Pollution from ships is also a problem.
See main article: Marine debris. Marine debris is human-created waste that ends up floating in the sea. Oceanic debris tends to accumulate at the centre of gyres and coastlines, frequently washing aground where it is known as beach litter. Eighty percent of all known marine debris is plastic - a component that has been rapidly accumulating since the end of World War II.[43] Plastics accumulate because they don't biodegrade as many other substances do; while they will photodegrade on exposure to the sun, they do so only under dry conditions, as water inhibits this process.[44]
Discarded plastic bags, six-pack rings and other forms of plastic waste which finish up in the ocean present dangers to wildlife and fisheries.[45] Aquatic life can be threatened through entanglement, suffocation, and ingestion.[46] [47] [48]
Nurdles, also known as mermaids' tears, are plastic pellets typically under five millimetres in diameter, and are a major contributor to marine debris. They are used as a raw material in plastics manufacturing, and are thought to enter the natural environment after accidental spillages. Nurdles are also created through the physical weathering of larger plastic debris. They strongly resemble fish eggs, only instead of finding a nutritious meal, any marine wildlife that ingests them will likely starve, be poisoned and die.[49]
Many animals that live on or in the sea consume flotsam by mistake, as it often looks similar to their natural prey.[50] Plastic debris, when bulky or tangled, is difficult to pass, and may become permanently lodged in the digestive tracts of these animals, blocking the passage of food and causing death through starvation or infection.[51] Tiny floating particles also resemble zooplankton, which can lead filter feeders to consume them and cause them to enter the ocean food chain. In samples taken from the North Pacific Gyre in 1999 by the Algalita Marine Research Foundation, the mass of plastic exceeded that of zooplankton by a factor of six.[43] [52] More recently, reports have surfaced that there may now be 30 times more plastic than plankton, the most abundant form of life in the ocean.[53]
Toxic additives used in the manufacture of plastic materials can leach out into their surroundings when exposed to water. Waterborne hydrophobic pollutants collect and magnify on the surface of plastic debris,[54] thus making plastic far more deadly in the ocean than it would be on land. Hydrophobic contaminants are also known to bioaccumulate in fatty tissues, biomagnifying up the food chain and putting great pressure on apex predators. Some plastic additives are known to disrupt the endocrine system when consumed, others can suppress the immune system or decrease reproductive rates.
See also: Mercury in fish. Apart from plastics, there are particular problems with other toxins which do not disintegrate rapidly in the marine environment. Heavy metals are metallic chemical elements that have a relatively high density and are toxic or poisonous at low concentrations. Examples are mercury, lead, nickel, arsenic and cadmium. Other persistent toxins are PCBs, DDT, pesticides, furans, dioxins and phenols.
Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation. They are also known to accumulate in benthic environments, such as estuaries and bay muds: a geological record of human activities of the last century.
Some specific examples are
See main article: Eutrophication. Eutrophication is an increase in chemical nutrients, typically compounds containing nitrogen or phosphorus, in an ecosystem. It can result in an increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.
The biggest culprit are rivers that empty into the ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. An excess of oxygen depleting chemicals in the water can lead to hypoxia and the creation of a dead zone.[67]
Surveys have shown that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%.[68] Estuaries also tend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters the marine environment in a confined channel. The World Resources Institute has identified 375 hypoxic coastal zones around the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, and East Asia, particularly in Japan.[69] In the ocean, there are frequent red tide algae blooms[70] that kill fish and marine mammals and cause respiratory problems in humans and some domestic animals when the blooms reach close to shore.
In addition to land runoff, atmospheric anthropogenic fixed nitrogen can enter the open ocean. A study in 2008 found that this could account for around one third of the ocean's external (non-recycled) nitrogen supply and up to three per cent of the annual new marine biological production.[71] It has been suggested that accumulating reactive nitrogen in the environment may have consequences as serious as putting carbon dioxide in the atmosphere.[72]
See main article: Ocean acidification. The oceans are normally a natural carbon sink, absorbing carbon dioxide from the atmosphere. Because the levels of atmospheric carbon dioxide are increasing, the oceans are becoming more acidic.[73] [74] The potential consequences of ocean acidification are not fully understood, but there are concerns that structures made of calcium carbonate may become vulnerable to dissolution, affecting corals and the ability of shellfish to form shells.
A report from NOAA scientists published in the journal Science in May 2008 found that large amounts of relatively acidified water are upwelling to within four miles of the Pacific continental shelf area of North America. This area is a critical zone where most local marine life lives or is born. While the paper dealt only with areas from Vancouver to northern California, other continental shelf areas may be experiencing similar effects.[75]
See main article: Environmental effects of fishing. Fishing nets that have been left or lost in the ocean by fishermen are called ghost nets, and can entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and other creatures. Acting as designed, these nets restrict movement, causing starvation, laceration and infection, and—in those that need to return to the surface to breathe—suffocation.[76]
Fishing operations often use trawl netting dragging and dredging them across the ocean bottom. Numerous habitats and ecosystems are disturbed and destroyed by trawling including coral reefs, sediments, and grasses that provide feeding and breeding grounds for a plethora of marine organisms. Coastal habitats such as mangroves are often sites of aquaculture farming practices in which the mangroves are either destroyed for easier use of the land or experience harmful conditions due to the farm being abandoned once the area becomes too polluted with excess nutrients.[77]
See main article: Overfishing. Some specific examples of overfishing.
Our World in Data provides a figure showing the trend in global fishing exploitation over a few decades to reveal the intensifying circumstances at hand:
Overfishing presents many threats to fish population densities, obviously. However, as these populations plummet below the maximum sustainable yield (MSY) value for the specific population, you are now risking the loss of biodiversity and possibility for extinction due to less diversity. This loss in diversity is especially concerning as we deal with environmental changes from climate change since less diversity decreases a populations ability to adapt and survive the alterations of the habitat.
See main article: Biodiversity. Each species in an ecosystem is affected by the other species in that ecosystem. There are very few single prey-single predator relationships. Most prey are consumed by more than one predator, and most predators have more than one prey. Their relationships are also influenced by other environmental factors. In most cases, if one species is removed from an ecosystem, other species will most likely be affected, up to the point of extinction.
Species biodiversity is a major contributor to the stability of ecosystems. When an organism exploits a wide range of resources, a decrease in biodiversity is less likely to have an impact. However, for an organism which exploit only limited resources, a decrease in biodiversity is more likely to have a strong effect.
Reduction of habitat, hunting and fishing of some species to extinction or near extinction, and pollution tend to tip the balance of biodiversity. For a systematic treatment of biodiversity within a trophic level, see unified neutral theory of biodiversity.
The global standard for recording threatened marine species is the IUCN Red List of Threatened Species.[82] This list is the foundation for marine conservation priorities worldwide. A species is listed in the threatened category if it is considered to be critically endangered, endangered, or vulnerable. Other categories are near threatened and data deficient.
Many marine species are under increasing risk of extinction and marine biodiversity is undergoing potentially irreversible loss due to threats such as overfishing, bycatch, climate change, invasive species and coastal development.
By 2008, the IUCN had assessed about 3,000 marine species. This includes assessments of known species of shark, ray, chimaera, reef-building coral, grouper, marine turtle, seabird, and marine mammal. Almost one-quarter (22%) of these groups have been listed as threatened.[83]
| Group | Species | Threatened | Near threatened | Data deficient | |
|---|---|---|---|---|---|
| Sharks, rays, and chimaeras | 17% | 13% | 47% | ||
| Groupers | 12% | 14% | 30% | ||
| Reef-building corals | 845 | 27% | 20% | 17% | |
| Marine mammals | 25% | ||||
| Seabirds | 27% | ||||
| Marine turtles | 7 | 86% |
An ambitious project, called the Global Marine Species Assessment, is under way to make IUCN Red List assessments for another 17,000 marine species by 2012. Groups targeted include the approximately 15,000 known marine fishes, and important habitat-forming primary producers such mangroves, seagrasses, certain seaweeds and the remaining corals; and important invertebrate groups including molluscs andechinoderms.[83]
Freshwater fisheries have a disproportionately high diversity of species compared to other ecosystems. Although freshwater habitats cover less than 1% of the world's surface, they provide a home for over 25% of known vertebrates, more than 126,000 known animal species, about 24,800 species of freshwater fish, molluscs, crabs and dragonflies, and about 2,600 macrophytes.[83] Continuing industrial and agricultural developments place huge strain on these freshwater systems. Waters are polluted or extracted at high levels, wetlands are drained, rivers channelled, forests deforestated leading to sedimentation, invasive species are introduced, and over-harvesting occurs.
In the 2008 IUCN Red List, about 6,000 or 22% of the known freshwater species have been assessed at a global scale, leaving about 21,000 species still to be assessed. This makes clear that, worldwide, freshwater species are highly threatened, possibly more so than species in marine fisheries.[84] However, a significant proportion of freshwater species are listed as data deficient, and more field surveys are needed.[83]
See main article: Fisheries management.
See also: Sustainable fishing.
A recent paper published by the National Academy of Sciences of the USA warns that: "Synergistic effects of habitat destruction, overfishing, introduced species, warming, acidification, toxins, and massive runoff of nutrients are transforming once complex ecosystems like coral reefs and kelp forests into monotonous level bottoms, transforming clear and productive coastal seas into anoxic dead zones, and transforming complex food webs topped by big animals into simplified, microbially dominated ecosystems with boom and bust cycles of toxic dinoflagellate blooms, jellyfish, and disease".[85]