314
Y. Olsen et al.
choices of technology also in the future. Sea-ranching and pond systems have limited cultural tradition in the western world, but it is important in Asia. Pond cultures
do generally not comply with the requirements of intensive cultivation (see above).
The available technology of mariculture represents a constraint for the innovation
response that may follow a specific problem.
10.5.1 Ponds and Sea Ranching
Ponds were, as mentioned above, the traditional low-technological systems, and sea
ranching also has a relatively long history. These methods were developed over
time to great extent through trials and errors. Sea ranching represents low-intensive
mariculture, with production within the carrying capacities of nature. Such methods
are often mentioned as extensive mariculture, with low production as compared to
most other methods. The methods of intervening with nature during sea ranching
are selective stocking of juveniles, predator control, and a careful selection or
improvements of the habitat. Other means of controlling this type of production are
virtually absent. Juveniles of fish and most other groups that are restocked are normally produced in land-based farms, but the seed can also be collected from natural
spawning habitats. Restocking of populations in coastal waters is a widely used
technique in East and South-East Asia, but such techniques were introduced also in
Western countries already in the first part of the 20th century (Svåsand and
Moksness 2004). These techniques are currently used for salmonids, for example
in Western Europe (Aprahamian et al. 2003), whereas Asian countries may restock
most of their important stocks of fish and shellfish in coastal waters.
Ponds are still widely used in most parts of the world, particularly for shrimps,
fish and a variety of other organisms. The techniques used are currently highly
diverse depending on the type of organism cultured, climate, and the environmental
and cultural conditions. Pond and concrete culture systems, which can be characterized
as closely related, are most suitable for semi-extensive mariculture, because the
means of maintaining control of cultivation is relatively poor. Pond culture is not
suitable for maintaining high exchange rates of water, which is perhaps the strongest
means available for controlling environmental and biological conditions in cultures.
Pond systems are also relatively shallow, with strong benthic-pelagic interactions.
Even a moderate accumulation of wastes in sediments will therefore easily affect
living conditions of the cultured animals. There are major efforts made to increase
feeding of pond culture in order to increase production, for example of high valued
shrimps, but these attempts have some times failed (Fast and Leung 2003). Means
to enhance the carrying capacity of pond culture are for example strong aeration or
oxygenation, water circulation, regular draining/cleaning procedures with removal
of sediments, and introduction of scavenger organisms that may utilize wastes from
the original organism (multi-trophic culture). The history of the last decades has
shown that slightly intensified pond cultures can be controlled adequately, but it is
even clearer that such systems are not adequate for intensive production.
Phytoplankton blooms, anoxia, frequent outbreaks of diseases with collapses of
Y. Olsen et al.
choices of technology also in the future. Sea-ranching and pond systems have limited cultural tradition in the western world, but it is important in Asia. Pond cultures
do generally not comply with the requirements of intensive cultivation (see above).
The available technology of mariculture represents a constraint for the innovation
response that may follow a specific problem.
10.5.1 Ponds and Sea Ranching
Ponds were, as mentioned above, the traditional low-technological systems, and sea
ranching also has a relatively long history. These methods were developed over
time to great extent through trials and errors. Sea ranching represents low-intensive
mariculture, with production within the carrying capacities of nature. Such methods
are often mentioned as extensive mariculture, with low production as compared to
most other methods. The methods of intervening with nature during sea ranching
are selective stocking of juveniles, predator control, and a careful selection or
improvements of the habitat. Other means of controlling this type of production are
virtually absent. Juveniles of fish and most other groups that are restocked are normally produced in land-based farms, but the seed can also be collected from natural
spawning habitats. Restocking of populations in coastal waters is a widely used
technique in East and South-East Asia, but such techniques were introduced also in
Western countries already in the first part of the 20th century (Svåsand and
Moksness 2004). These techniques are currently used for salmonids, for example
in Western Europe (Aprahamian et al. 2003), whereas Asian countries may restock
most of their important stocks of fish and shellfish in coastal waters.
Ponds are still widely used in most parts of the world, particularly for shrimps,
fish and a variety of other organisms. The techniques used are currently highly
diverse depending on the type of organism cultured, climate, and the environmental
and cultural conditions. Pond and concrete culture systems, which can be characterized
as closely related, are most suitable for semi-extensive mariculture, because the
means of maintaining control of cultivation is relatively poor. Pond culture is not
suitable for maintaining high exchange rates of water, which is perhaps the strongest
means available for controlling environmental and biological conditions in cultures.
Pond systems are also relatively shallow, with strong benthic-pelagic interactions.
Even a moderate accumulation of wastes in sediments will therefore easily affect
living conditions of the cultured animals. There are major efforts made to increase
feeding of pond culture in order to increase production, for example of high valued
shrimps, but these attempts have some times failed (Fast and Leung 2003). Means
to enhance the carrying capacity of pond culture are for example strong aeration or
oxygenation, water circulation, regular draining/cleaning procedures with removal
of sediments, and introduction of scavenger organisms that may utilize wastes from
the original organism (multi-trophic culture). The history of the last decades has
shown that slightly intensified pond cultures can be controlled adequately, but it is
even clearer that such systems are not adequate for intensive production.
Phytoplankton blooms, anoxia, frequent outbreaks of diseases with collapses of