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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.
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 fertiliser.
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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