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| | | Land and water aquaculture resources |
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|  Aquaculture depends, like agriculture, on the earth's natural resources for its production. To date, its development has been restricted to water bodies on land, or to sea sites close to the coast, but with 70% of the earth's surface being covered by water, the potential for aquaculture to expand to help to meet future human food needs is considerable. | | | | Production is largely derived from land-based freshwater culture systems. These continue to have considerable potential for further expansion, particularly the multiple resource use systems that are integrated with agriculture and irrigation. The marine environment offers resources for aquaculture which remain largely to be explored.A wide variety of animal and plant species are produced through aquaculture: finfish; shrimp, prawns and crabs; clams,oysters and mussels; as well as seaweeds and .other aquatic plantsAquaculture provides about one third, or 40 million metric tonnes, of the annual world fisheries production of 120 million metric tonnes. Half of all aquaculture production is finfish, a quarter is aquatic plants and the remaining quarter is made up of crustacea (such as shrimp, prawns, crabs) and molluscs such as clams, oysters and mussels.The most harvested species in recent years has been the Pacific Oyster (Crassostrea gigas), which grossed 3.4 million metric tonnes in 1998. The Pacific Oyster was the number one aquaculture species in four out of the five years to 1998.A close second is a freshwater fish, the Silver Carp (Hypophthalimichthys molitrix) which contributes more than 3 million metric tonnes per year to world totals. Silver Carp are grown in ponds, mainly in Asia, and eat tiny plankton. In the early 1990s they were the world's leading aquaculture species, until 1994 when the Pacific Oyster took over. Given its higher yield of meat compared to the oyster, it is arguable that the Silver Carp is still the world's most important aquaculture species.Seven out of the ten top species are freshwater finfish and six of those are carps. The other three species figuring in the top ten are molluscs.Carps accounted for nearly half of the 31 million metric tonnes of fish and molluscs produced by farming in 1998. Molluscs also made a major contribution (9.1 million mt) while production of farmed salmon, tilapia and shrimp totaled around 1 million metric tonnes each. Herbivores outnumber carnivores about ten to one in world aquaculture production.The Top Ten Species Produced by Aquaculture (1998)Pacific OysterCrassostrea gigasSilver CarpHypophthalmicthysmolitrixGrass carpCtenopharyngodonidellusCommon CarpCyprinus carpioBighead CarpHypophthalmicthysnobilisJapanese Carpet ShellRuditapesphilippinarumCrucian CarpCarassiuscarassiusYesso ScallopPecten yessoensisNile TilapiaOreochromisniloticusRoho CarpLabeo rohitaThe aquatic plants produced include brown, red and green seaweeds, grown for direct use as food and also for the extraction of alginate and carageenan (agar-agar). Half of the total 1998 production was of just one species, the Japanese Kelp (Laminaria japonicus), 90 percent of which is grown in China.Freshwater fish are the most important aquaculture group by volume and make the greatest contribution to the human food supply. However, some of the minor product groups such as shrimp and marine fish have a disproportionate economic importance because of their high unit value. Farmed freshwater fish, for instance, had an average value of US$1.14 per kg in 1998, while marine fish came in at US$4.35 and crustacea at US$5.90 per kg.Overall most of the major aquaculture product groups exhibited a two- to three-fold growth during the 1990s with some individual species increasing even more. World production of the Chinese River Crab (Eriocheir sinensis), for example, expanded twenty-five fold between 1989 and 1998 (from 5 000 to 123 000 mt). Other notable increases include the Giant Freshwater Prawn (Macrobrachium rosenbergii) with a six-fold growth, the Black Carp (Mytopharyngodon piceus) with a 4-fold growth and the Japanese Carpet Shell (Ruditapes philippinarum) with a 5-fold growth. The sector of high value marine finfish (such as seabass, grouper and mandarin fish) is also experiencing a strong expansion driven by demand in affluent Asian markets, especially for the live product.Whilerecent attention has focused on the adverse impacts of introduced species - also known as alien species and alien genotypes - species introductionsare a valid means to improve production and economic benefit from fisheries and aquaculture.Approximately 17 percent of the world's finfish production is due to alien species. Production of the African cichlid tilapiais much higher in Asia(greater than 700 000 metric tonnes in 1996) than in most areas of Africa(39 245 metric tonnes). Introduced salmonidsin Chilesupport a thriving aquaculture industry that is responsible for approximately 20 percent of the world's farmed salmon and directly employs approximately 30 000 people.Introduced species may have environmental as well as social and economic impacts . Aquatic ecosystems may be affected by the introduced species through predation, competition, mixing of exotic genes, habitat modification and the introduction of pathogens. Human communities may also be impacted through change in fishing patterns due to a newly- established fishery or through changes in land use and resource access when high valued species are introduced into an area.The practice of using species outside their natural range to increase production or profitability can be expected to continue.The issue is not to ban alien species - or to abandon regulation of their movement - but rather to assess associated risks and benefits and then, if appropriate, develop and implement a plan for their responsible use.One mechanism to assist in the responsible use of introduced species is the development of codes of practice such as have been developed by the International Council for the Exploration of the Sea and the European Inland Fishery Advisory Commission.Significant international instruments have recently been established to address the issue of species introductions, such as the Convention on Biological Diversity and the FAO Code of Conduct for Responsible Fisheries. These codes and conventions call for accurate assessments of the risks of using exotic species and are promoting the creation of information sources and an exchange of information on exotic species, their biological and ecological attributes, and potential impacts (both positive and negative). The problem is how to determine the impact of a proposed introduction into complex and dynamic aquatic ecosystems where our information base is often inadequate.Toward this end, FAO Fisheries Department has created the Database on Introductions of Aquatic Species (DIAS) to serve as an important initial summary and registry of introduced species. This database has been incorporated into FishBase, a relational database that contains a variety of information on approximately 20 000 of the world's species of finfish. | | | | Aquaculture can be a very productive use of land, with the amount of food produced per hectare considerably higher than with arable farming or livestock rearing. And in many aquaculture operations, there are extra benefits from the multiple use of resources. Fish can be grown in rice fields, for instance, with gains for both crops from the cycling of nutrients and the control of insect pests. Small-scale farmers can combine poultry or pig production with the growing of cereals or vegetables and the rearing of fish, making optimum use of sometimes-scarce resources. Along the coasts, as long as aquaculture development is well planned, farming activities can have beneficial effects on the local environment, for instance by supplying needed nutrients to mangrove forests. | | | | Much aquaculture production currently comes from small freshwater ponds in the tropics, but farmers can be found operating in such diverse locations as cold lakes high in the mountains, producing trout, or in the middle of the Arizona desert, farming shrimp. | | | | In coastal waters, there can be potential conflicts with other uses of land and water resources- - tourism, agriculture, navigation, wildlife, capture fisheries. It is important that development planning takes account of these diverse interests and that the stakeholders have a full opportunity to participate in the planning process. Putting an economic value on the various potential uses of water bodies on land and sea is a developing field that is helping to provide the tools needed to make the right development decisions. | | | | The use of land and water resources by aquaculture can be very diverse. For example, along the coasts, sheltered bays provide sites for the rearing of oysters, scallops and mussels. These are mainly grown on ropes hung from rafts or buoyed lines, but they can be farmed also on racks or poles attached to the seabed. Seaweed culture is practised in shallow waters close to coasts. There is potential to bring benefits to coastal water quality through achieving the right balance in such areas between fish rearing (that tends to increase the nutrients in the water) and molluscs and seaweeds (that tend to decrease them). | | | | In waters close to shore, usually in sheltered locations, farmers install net cages for rearing fish like bass, grouper, bream or salmon. Ponds built on the landward side of the beach are used for farming marine fish like milkfish, mullet or seabass, for growing shrimp, or fattening lobsters. | | | | Developing technologies are beginning to open up the opportunity to rear fish in more exposed locations further away from the coasts or even out in the open ocean. Sturdy cages that can withstand heavy seas, or submerged cages that are kept below the stormy surface zone and only raised for maintenance, could allow vast new areas of sea to be developed for aquaculture food production. At the same time moving the production offshore reduces the potential for adverse environmental effects on sensitive coastal zones and the likelihood of conflict with other users. | | | | On land, still water ponds are the main sites for aquaculture, but many countries have fish cages operating in rivers or large lakes and reservoirs and some fish like tilapia or trout can be reared in raceways built along side fast flowing rivers. In the right location, the effluent from a raceway fish farm can be used to irrigate arable land, the nutrients from the fish production benefiting the plants as fertilizer. | | | | Much of the potential for aquaculture has not been realised, both on land and water, but the contribution of aquaculture to food production, particularly for the poor, can be substantial. A number of modern techniques are developing to help identify promising areas for aquaculture development, including for instance, the analysis of satellite imagery (a key component of 'GIS' or Geographic Information Systems). This can be a great help in national and regional planning to move towards tapping aquaculture's full potential. | | | | |
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