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D. Whitmarsh and M.G. Palmieri
value of seagrass estimated by the Florida Department of Environmental Protection
is $20,500 per acre per year (Anon 2003), a remarkably high figure which presumably owes much to the role of seagrass in maintaining water clarity (crucial for
recreation). If the value of seagrass in the Mediterranean were shown to be of a
similar order of magnitude it would clearly have important implications for policies
aimed at protecting this habitat from anthropogenic threats, whether from aquaculture or some other source.
Land subsidence and saline intrusion have been shown to be linked to aquaculture, in both cases resulting in measurable economic costs. In Taiwan, growth of
aquaculture has been accompanied by increasing demand for fresh water, which has
led to overuse of underground supplies and consequent land subsidence (Huang
1990). This in turn has given rise to a wide range of negative externalities, notably:
damage to property and agriculture due to sea water intrusion; salinization of fresh
water supplies; production losses to fish farmers due to deteriorating drainage and
sanitary conditions; and destruction of infrastructures (i.e., roads, ditches, sea dikes,
etc.). Huang (1990) formulates an econometric model to estimate these effects in
the case of one of the main species (grass shrimp), the results showing that the net
social benefits of aquaculture vary widely across regions but are on average negative. These demonstrate the burden on society imposed by the growth of aquaculture, and ‘strongly signal the necessity of reformulating the fishery structure and the
natural resource policies in Taiwan.’ In the Mekong Delta, the adoption of shrimp
farming has seen the appearance of a number of environmental problems that have
impacted negatively on rice growers as well as fish farmers themselves (Tran et al.
1999). Off-site impacts include the salinization of adjacent rice monoculture areas,
while the main on-site impact has been siltation of ponds and fields due to turbid
water inundation. To investigate the extent of these problems and to estimate their
economic cost, Tran et al. (1999) conducted a survey of households engaged in
shrimp production (either as monoculture or integrated with rice) and rice monoculture. The results revealed that salinization added to the costs per hectare in rice
growing areas, and this was supported by other evidence showing that rice growers
situated close to shrimp farms had reduced yields. Removal of sediment also
imposed a significant financial burden on farmers, and while this might strictly be
regarded as an ‘internal’ rather than an ‘external’ cost, the authors emphasise that
the loss of land could have long term implications that farmers might disregard in
their decision-making.
Aquaculture may interact with commercial fisheries to engender a range of
externalities, though not all of these are negative. A number of studies have shown
that the entry of aquaculture producers into a market may have a beneficial effect
where, by diverting demand, it reduces harvesting pressure on over-exploited capture fisheries and allows natural stocks to recover. The result may thus be to
increase overall supply and reduce the price of wild-caught fish, benefiting consumers (Anderson 1985). The magnitude of this effect will be stronger where the
products from these two sources of supply, the capture fishery and the aquaculture
sector, are regarded by the market as close substitutes (Ye and Beddington 1996).
Interactions with the feed fishery add an additional layer of complication, and it is
D. Whitmarsh and M.G. Palmieri
value of seagrass estimated by the Florida Department of Environmental Protection
is $20,500 per acre per year (Anon 2003), a remarkably high figure which presumably owes much to the role of seagrass in maintaining water clarity (crucial for
recreation). If the value of seagrass in the Mediterranean were shown to be of a
similar order of magnitude it would clearly have important implications for policies
aimed at protecting this habitat from anthropogenic threats, whether from aquaculture or some other source.
Land subsidence and saline intrusion have been shown to be linked to aquaculture, in both cases resulting in measurable economic costs. In Taiwan, growth of
aquaculture has been accompanied by increasing demand for fresh water, which has
led to overuse of underground supplies and consequent land subsidence (Huang
1990). This in turn has given rise to a wide range of negative externalities, notably:
damage to property and agriculture due to sea water intrusion; salinization of fresh
water supplies; production losses to fish farmers due to deteriorating drainage and
sanitary conditions; and destruction of infrastructures (i.e., roads, ditches, sea dikes,
etc.). Huang (1990) formulates an econometric model to estimate these effects in
the case of one of the main species (grass shrimp), the results showing that the net
social benefits of aquaculture vary widely across regions but are on average negative. These demonstrate the burden on society imposed by the growth of aquaculture, and ‘strongly signal the necessity of reformulating the fishery structure and the
natural resource policies in Taiwan.’ In the Mekong Delta, the adoption of shrimp
farming has seen the appearance of a number of environmental problems that have
impacted negatively on rice growers as well as fish farmers themselves (Tran et al.
1999). Off-site impacts include the salinization of adjacent rice monoculture areas,
while the main on-site impact has been siltation of ponds and fields due to turbid
water inundation. To investigate the extent of these problems and to estimate their
economic cost, Tran et al. (1999) conducted a survey of households engaged in
shrimp production (either as monoculture or integrated with rice) and rice monoculture. The results revealed that salinization added to the costs per hectare in rice
growing areas, and this was supported by other evidence showing that rice growers
situated close to shrimp farms had reduced yields. Removal of sediment also
imposed a significant financial burden on farmers, and while this might strictly be
regarded as an ‘internal’ rather than an ‘external’ cost, the authors emphasise that
the loss of land could have long term implications that farmers might disregard in
their decision-making.
Aquaculture may interact with commercial fisheries to engender a range of
externalities, though not all of these are negative. A number of studies have shown
that the entry of aquaculture producers into a market may have a beneficial effect
where, by diverting demand, it reduces harvesting pressure on over-exploited capture fisheries and allows natural stocks to recover. The result may thus be to
increase overall supply and reduce the price of wild-caught fish, benefiting consumers (Anderson 1985). The magnitude of this effect will be stronger where the
products from these two sources of supply, the capture fishery and the aquaculture
sector, are regarded by the market as close substitutes (Ye and Beddington 1996).
Interactions with the feed fishery add an additional layer of complication, and it is