Land and water resources
Wood Brothers' shrimp farm in the desert of Arizona, United States
Courtesy of Wood Brothers
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.
Aquaculture can be a very productive use of land, in some cases 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. In some cases, significant benefit and efficiency in resource use can be achieved through integration of aquaculture into existing agricultural practices. 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 in the United States, farming shrimp.
Scallops grow on ropes suspended in sheltered bays
Courtesy of NACA Bangkok
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.
A cage designed for rough waters offshore
Courtesy of Farmocean
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 fertiliser.
Much of the potential for aquaculture has not been realized, 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.