Agriculture and Environment: Shrimp

Environmental Impacts of Production: Siting & Coastal Habitats

There is good evidence that as many as 90% of all of the environmental problems from shrimp aquaculture arise from where the ponds are built (Boyd and Clay 1998).

The impacts include the loss of habitat, interference with ecosystem hydrology, and loss of coastal barriers that prevent storm damage.


Siting can also accentuate the eventual impacts of on-farm management practices. If an operation is not built in the right place it will be hard to get to, and roads and other necessary infrastructure may cause problems unnecessarily.

Water quality issues
Poor siting can also lead to poor water quality or the inability to evacuate effluents. Siting is also the single largest source of conflicts with local communities and other resource users.

For those who can afford to buy the best-suited pieces of land for shrimp aquaculture, the overall siting of operations is not generally an issue, at least from an environmental point of view.

Siting considerations for smaller units
In addition, more is known today about the best sites for shrimp aquaculture. New ponds established after a search for better sites are not generally a problem. However, for those small-scale producers who are trying to grow shrimp on the piece of land they already own, this can be a very important issue.

Without simply closing poorly sited ponds or even entire operations in some instances, it is very difficult to address their problems. Some problem sites can be remedied if the ponds are relatively small and if the water can be pumped to another containment area or discharged into a canal where it can be treated.

Impacts of high area density of ponds
New ponds that are built after the best sites have already been developed can also pose environmental threats. By themselves, many such operations would probably be able to operate within acceptable environmental parameters. However, the cumulative impacts of having many operations built in the same area often exceed the local carrying capacity.

This is most often a problem when producers take chances on developing more marginal areas because they are the only unoccupied sites available in an area where everyone is apparently getting rich from producing shrimp.

5-10% loss of mangrove habitat globally!
Shrimp farming alone appears to be responsible for some 5-10% of the global loss of mangrove habitat (Boyd and Clay 1998). Yet in some countries it has caused as much as 20% of the damage to mangrove areas, and in some watersheds shrimp farming accounts for virtually all mangrove destruction.

In part this situation resulted from the advice of experts who initially thought that because shrimp spend part of their lives there, mangrove habitats were the best sites for shrimp farms. Over time, it became clear that the acid soils of mangrove habitats were not suitable for shrimp ponds. But the damage to these ecosystems had already been done.

Continued depletion due to low costs
Another factor complicating this issue was that many development agencies wanted to help the poor. Building shrimp ponds in tidal areas saved farmers the expense of water pumps and long-term pumping costs.

Today, while it is generally known that mangrove areas are not the best sites for shrimp ponds, farmers will still build there because land is cheap or free, there are no conflicts with other agriculturalists, and profits from even a couple of years make the efforts attractive financially.

Conversion of fragile coastal habitats
Shrimp aquaculture has also been responsible for the conversion of other fragile coastal habitats in the tropics. Little attention has been given to the loss of mud and salt flats, coastal estuaries, and wetlands to shrimp aquaculture. It is now known that while such areas are not the permanent homes for much biodiversity, many are seasonally quite important in the life cycles of some species. Furthermore, they are important from an ecosystem point of view.

A few hundred thousand hectares of coastal areas may have been converted to shrimp farms that failed and were then abandoned. These areas include a wide range of former habitats. Unfortunately, most failed shrimp operations are not required to recreate the hydrology of the coastal areas that they degraded. In many cases, simply opening the dikes so that the water could flow would re-establish the areas again.

Credits

Extracts from "World Agriculture & Environment" by Jason Clay - buy the book online from Island Press

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