18.2. The Model
397
aquaculture was meeting over 25% of the wo rld's demand (Clay 1996).
Since 1989, it has continued to increase its market share, though the outbreak of disease in some countries slowed the growth of the indu stry.
Many shrimp aquaculturists rely on wild-caught, postlarval shrimp to stock
their ponds , but the process of capturing this seedstock has an associated bycatch that is estimated to be even higher than wild fisheries by-catch (Boyd
1998). The sites chosen for ponds, especially during the 1980s and early
1990s, were primarily in mangrove-forested coastal areas, causing large-scale
clearing (Hagler 1998). These sites provided easy access to fresh seawater for
use in the ponds. Though the clearing of mangroves has been stopped by
many governments, most existing ponds still displace mangroves. Since mangroves provide habitat for many plant and animal species, biodiversity is adversely affected by this type of pond siting. The low-tech, low-density practices of the past allowed aquaculturists to cycle waters from coastal ponds
into estuaries with little effect. But as pond density increases in coastal areas
and as technology allows for higher density within the ponds , higher levels
of effluents, in the form of nutrients, drugs (including antibiotics), and chemicals are released into coastal waters. Where aquaculture pond water is gathered from polluted waterways, the incidence of shrimp disease has increased
considerably (Rosenberry 1999). It is not known what effect these pollutants
are having on the reproduction of wild populations. Wild shrimp are dependent on coastal waters for maturation from the postlarval state until they are
ready to return to the open seas to reproduce (Upton 1992). Because of its
dependence on wild-caught seedstock, aquaculture production will be affected by any decrease in wild shrimp populations.
Through out the 1990s, standards for sustainable aquaculture-shrimp production have been under development by people associated with the industry and by others in environmental organizations (Boyd 1998). There is
still disagreement about the nature of sustainable practices, as we ll as how
these standards are to be applied and enforced. Clarification of these issues
is one of the things to be considere d in the next ph ase of this project.
18.2. The Model
There are a number of feedba cks present in the global shrimp market.
These include competition between two suppliers, fisheries and aquaculture , the reciprocal relation between price and demand, the effects of regulation on one industry segment or the other, and the effects of policy decisions on key stakeholders and the environment. A simple computer
model is presented here to examine the feedback relations in more detail.
The model was develop ed with the participation of national governments,
NGOs, and industry.
The model consists of five sectors: Market Demand , Wild Shrimp Fisheries, Aquaculture , Financials, and Environment. The first sector is Market
397
aquaculture was meeting over 25% of the wo rld's demand (Clay 1996).
Since 1989, it has continued to increase its market share, though the outbreak of disease in some countries slowed the growth of the indu stry.
Many shrimp aquaculturists rely on wild-caught, postlarval shrimp to stock
their ponds , but the process of capturing this seedstock has an associated bycatch that is estimated to be even higher than wild fisheries by-catch (Boyd
1998). The sites chosen for ponds, especially during the 1980s and early
1990s, were primarily in mangrove-forested coastal areas, causing large-scale
clearing (Hagler 1998). These sites provided easy access to fresh seawater for
use in the ponds. Though the clearing of mangroves has been stopped by
many governments, most existing ponds still displace mangroves. Since mangroves provide habitat for many plant and animal species, biodiversity is adversely affected by this type of pond siting. The low-tech, low-density practices of the past allowed aquaculturists to cycle waters from coastal ponds
into estuaries with little effect. But as pond density increases in coastal areas
and as technology allows for higher density within the ponds , higher levels
of effluents, in the form of nutrients, drugs (including antibiotics), and chemicals are released into coastal waters. Where aquaculture pond water is gathered from polluted waterways, the incidence of shrimp disease has increased
considerably (Rosenberry 1999). It is not known what effect these pollutants
are having on the reproduction of wild populations. Wild shrimp are dependent on coastal waters for maturation from the postlarval state until they are
ready to return to the open seas to reproduce (Upton 1992). Because of its
dependence on wild-caught seedstock, aquaculture production will be affected by any decrease in wild shrimp populations.
Through out the 1990s, standards for sustainable aquaculture-shrimp production have been under development by people associated with the industry and by others in environmental organizations (Boyd 1998). There is
still disagreement about the nature of sustainable practices, as we ll as how
these standards are to be applied and enforced. Clarification of these issues
is one of the things to be considere d in the next ph ase of this project.
18.2. The Model
There are a number of feedba cks present in the global shrimp market.
These include competition between two suppliers, fisheries and aquaculture , the reciprocal relation between price and demand, the effects of regulation on one industry segment or the other, and the effects of policy decisions on key stakeholders and the environment. A simple computer
model is presented here to examine the feedback relations in more detail.
The model was develop ed with the participation of national governments,
NGOs, and industry.
The model consists of five sectors: Market Demand , Wild Shrimp Fisheries, Aquaculture , Financials, and Environment. The first sector is Market