Shrimp Farming and the Environment - Library

creeks, and sea-grass beds, fulfill a wide variety of functions. It is important not to ignore the nonmangrovecomponents of these ecosystems, which in some cases may be at least as valuable as themangrove.Estuarine and lagoon systems fulfill the following major functions:• Provide nurseries for inland, coastal, and offshore fisheries, including shrimp, fishes, andcrabs; and• Assimilate nutrients and use organic matter, turning some of it into sediment.Mangrove probably enhances these functions, and in addition:• Produces a range of wood and other forest products (firewood, poles, wood chips, charcoal,bark for tanning and dyes, honey, etc.);• Protects shoreline against flooding and inundation in storms; and• Increases sedimentation and accretion, and reduces erosion.It is also commonly claimed that mangrove has high biodiversity value. In fact, most mangrove forestitself is rather impoverished, consisting of few species due to its varying water level, salinity, anaerobicconditions, and low light. However, mangrove forests are important to the overall biodiversity of itswider estuarine systems, as a source of nutrients and detritus and as shelter for a variety of species.Mature mangrove also harbors many rare or unique species. These and other values and functions havebeen widely reported and described in the literature, and it is now widely accepted that mangroveconservation should be a high priority.Reduction of mangrove forestsMangroves constitute an important part of the tropical coastline. At one time, as much as 75% oftropical coastlines were likely covered with mangroves. The United Nations Environmental Program(UNEP) now estimates that about half of the world’s mangrove areas have been destroyed. Somemangroves have become established due to poor upland management practices, especially fromextractive industries such as forestry, agriculture, and mining, over the past few centuries (Clay 1998,personal communication).Mangroves are under intense pressure from a suite of development activities, including overexploitationfor firewood, poles, and charcoal production; conversion to agriculture, salt farming, andcoastal aquaculture; and urban development. The relative contribution of these different activities tomangrove destruction varies widely from country to country and region to region. Although the dataare incomplete and often contested, there is no doubt that shrimp farming has been a significant causeof destruction in some areas (Asian Development Bank/Network of Aquaculture Centres in Asia[ADB/NACA] 1995; Primavera 1991; Clay 1998; Boyd 1997.) In the countries that are the largestproducers of farmed shrimp, NACA reports that 20–50% of all current mangrove deforestation is dueto shrimp farming. In areas of Ecuador and Thailand, for example, large areas of mangrove may havebeen destroyed for shrimp ponds. In many instances, however, shrimp farms were constructed inmangrove areas that had previously been deforested for wood products, making it difficult to attributethe original cause of mangrove loss.Although mangroves are now widely recognized as being unsuitable for market-oriented shrimpaquaculture development for a variety of reasons (discussed below), primary or secondary mangroveforests are still converted to shrimp ponds in many countries. In Thailand, for example, governmentagencies have had little success in preventing the clearing of protected mangrove forests (MIDAS1995). Even in wetlands under consideration as RAMSAR sites, illegal shrimp farmers seeking newland have established their ponds (Anon. 1997a). Major shrimp producers from Thailand are reportedto have expanded into Koh Kong Province of Cambodia, where the environment minister has expressedconcern for the mangrove forests of the province.It should be remembered, however, that coastal resources, and in particular mangrove and estuarinesystems, have been under intense pressure from increased population and development demands formany years. Displaced and migrant people have often been forced into coastal areas, where they findopportunities to collect wood for fuel, charcoal, and poles, to make salt, and to fish. Significant area21