|Aquaculture - Initial Environmental Assessment Series No. 5 (NORAD, 1992)|
|Part I: General account|
Aquaculture is carried out in different kinds of ecosystems comprising all water types. Some tropical ecosystems affected by aquaculture are vulnerable to encroachments and are themselves conservation-worthy. Furthermore, aquaculture farms will in many cases affect environments already exploited for other purposes, causing conflicts with other activities over the utilization of land and water resources. Below is an overview of the different ecosystems and environment types in tropical areas and developing countries where aquaculture is being practiced, as well as the most likely forms of aquaculture in the respective areas:
1) Freshwater areas:
Freshwater environments account for the most common aquaculture environments in most developing countries. They comprise farming of various species of fish and freshwater shrimps. Freshwater farming comprises a series of different environments and forms of farming. The most common are:
Lakes: These comprise natural lakes as well as large man-made lakes and reservoirs. Semi-intensive and intensive forms of farming are the most common, and these are carried out both in shallow waters by means of enclosures or by the use of pens. Transitional forms towards fishery also occur (cf. booklet for initial environmental assessment of fisheries) where fish are restocked and caught as in ordinary fishing. The farms are run by farmers, fishermen as well as by more affluent layers of the population.
Large man-made ponds: Many extensive and semi-intensive farms for fish farming consist of relatively large, shallow ponds (c. 1.6 hectare or more) which can be drained and treated before the restocking of new farm organisms. These are often located in areas well supplied with nutrients and organic matter. The surrounding vegetation is often used as feed for herb-eating fish (herbivore). The ponds are usually located in agricultural areas and are commonly run by local farmers and/or fishermen.
Small man-made ponds: These ponds (smaller than 1.6 hectare) form the basis of a variety of types of extensive and semi-intensive farming, often in combination with other activities such as animal husbandry (e.g. ducks, hens) and agriculture. Farming in these ponds is often biologically complicated as several species are often cultivated simultaneously (polyculture). Such farms are usually run by local farmers. The farming of freshwater shrimps, on the other hand, is an intensive form which takes place in small ponds, usually managed by well-funded contractors.
Natural ponds, rivers and major canals: Such water bodies can be exploited for extensive and semi-intensive farming. This is done by means of enclosures and net pens. The farms are usually run by local people.
Rice fields and irrigation canals: These can, to a certain extent, be used for fish farming. Wild fish can be enclosed within the rice fields or restecked systematically in a common culture which can be utilized by the rice as well as the fish. The introduction of herb-eating fish controls the growth of weeds; some fish also eat vermin living on and off the rice plant or other local species.
2) Marine coastal areas:
Aquaculture in marine coastal areas takes place in both saltwater and brackish water, and comprises a series of different forms of farming.
Farming systems in saltwater are different with respect to choice of technology, species and environment. The most common forms are:
Fish farming in cages, pens and pen culture (bottom of the pen is formed by the lake or sea bottom) and enclo-sures: These are intensive forms of farming that exploit areas providing the farms with natural protection e.g. boys, inlets etc. The development of sea-cage farms with large, solid cages currently enables farming in more open and exposed localities, which greatly reduces competition with other user groups. These farms are commonly run by well-funded contractors.
Intertidal forming of shells, snails and seaweeds: These are extensive forms of farming that utilize areas offering natural protection against rough weather. The farming may consist of sea-floor cultures whereby the shells are scattered directly on the sea floor in the tidal zone or deeper down. Another form involves the placement of various types of stationary racks for the farming of seaweeds, or racks on which baskets for the farm organisms can be hung. A third type involves hanging cultures whereby the organisms hang freely in water in ropes and tapes from rains and sticks. Areas used for this kind of farming are often attractive for other activities as well, so that conflicts may occur between different user groups. Depending on the size of the farm, these forms of farming are practiced both by the poor and the more affluent parts of the population. intertidal farming of shrimps and fish: These are intensive and semi-intensive forms of farming. The areas being used can be marine lagoons and ponds or tanks on land which are situated in the tidal zone or nearby. Such forms of farming can in many cases affect mangrove swamps. The farms are usually operated by the affluent part of the population.
Restocking of fish - sea ranching: This involves restocking of fry in order to consolidate an existing stock of fish in naturally restricted areas, e.g. a bay, which is subsequently harvested as in ordinary fishing (cf. booklet for initial environmental assessment of fisheries).
b) Brackish water:
Farming in brackish water usually takes place in estuaries, which provide the farms with natural protection, and mangrove swamps, where the salinity is conducive to cultivation of both shrimp and fish species by means of methods that are equivalent to those described under saltwater above. One often finds large embankment ponds where the entrance can be controlled with a sluice, and which take advantage of the tide. The methods can be intensive, semi-intensive or extensive.
Ecosystems such as mangrove swamps and coral reefs are especially vulnerable to pollution and technical encroachments. They may, in themselves, be preservation-worthy types of nature, as well as being vital for the reproduction and growth of economically important species.
Many tropical water bodies - freshwater, brackish water and saltwater - are extremely low in nutrients. The nutrients are largely bound up with the existing flora and fauna. By a steady supply of nutrients, as in semi-intensive and intensive farming, the ecosystem may acquire a higher substance value. Besides, this may improve the production of other useful plants and animals. Yet problems of pollution and eutrophication in watercourses and coastal areas are more frequently the case (cf. chapter 3.3).
Tropical water bodies are often subject to considerable evaporation. In freshwater environments, therefore, it is important to ensure an adequate and stable water supply to the farms. In dry areas or areas with little rainfall, limited ground-water resources are sometimes used for aquaculture. Such a situation may require a survey of available water sources and other hydrological conditions before aquaculture farms are developed (cf. chapter 3.5). The water temperature can also be decisive with respect to which species can be cultivated.
Tropical soil often contains pyrite, which makes the water acidic
and unsuitable for farming. Areas which have already been used as embankment
ponds can be treated by covering the dam floor with special tarpaulins, or by
adding calcium to the water. This is resource consuming, however, and in order
to avoid such misplacement of aquaculture farms, soil tests should be taken
prior to a development.
The local social conditions relating to a project may vary greatly from place to place. In some areas aquaculture may have been practiced for generations, having become part of the local culture and tradition, whereas in other areas it has never been practiced. Large parts of Asia have long traditions of aquaculture, and it is more common there than in Africa and Central America. Farmers in developing countries are a heterogeneous group ranging from poor smallholders with a few fish in a small embankment pond to multinational companies engaged in sophisticated and intensive aquaculture. Between these are relatively affluent farmers and other rural and urban enterprisers.
In connection with the planning of aquaculture in areas where it has never been practiced, one should be aware that the local population may not have title to land or water. Such rights are often allocated according to traditional and complex arrangements, and may involve that a farmer, for example, has only limited or seasonal access to land and/or water resources (cf. chapter 3.6).