Aquaculture

Aquaculture is a booming business, due to the rapid growth in demand for high value marine products like salmon and shrimp. The recent expansion in production of these species is reflected in an explosive increase in the number of intensive culture operations in coastal areas. Improvements in yield per unit area have been achieved by using high value feedstock and by using antibiotics and pesticides to control diseases and parasites. While traditional extensive methods of shrimp production yield between 100 and 500 kg shrimp per hectare, intensive pond culture can increase this to 1000-10,000 kg per hectare.

There are many environmental problems associated with intensive aquaculture of marine species in the coastal zone. A clear example is the large-scale destruction of mangroves in Asia and Latin America for the construction of intensive aquaculture facilities. In the Philippines, aquaculture has contributed significantly to the removal of 75% of the original mangrove habitat. In Ecuador, the rapid growth of shrimp production had claimed 12,000 ha of virgin mangrove by 1987. Intensive shrimp ponds developed from mangroves are usually abandoned as soon as yields begin to fall. This occurs as a result of declining water quality. Poor husbandry and inadequate waste management cause outbreaks of disease. Subsequently, new areas are cleared and developed. The mean lifetime of such ponds in Thailand is estimated at only 7 years. This method of shrimp production is ultimately unsustainable. This became clear when aquaculture production crashed in Taiwan in the late 1980's due to high costs, pollution and disease. Such unsustainable 'shifting aquaculture' operations supply a large proportion of global shrimp production at the expense of destroying irreplaceable coastal ecosystem.

Intensive aquaculture emits large quantities of nutrients and organic matter into the environment. For every tonne of cage-farmed salmon produced, an estimated 2.5 tonnes of organic waste may be generated. In intensive shrimp ponds ammoniacal nitrogen is accumulated, which can be highly toxic to many marine species. Although both cage and pond aquaculture undoubtedly lead to local increases in nutrient loading, there is hardly any information on direct impacts. The aquaculture industry uses a variety of antibiotics, pesticides and detergents. Information on the types and quantities of chemicals employed in many countries is very scarce. Many of the chemicals used to control disease are toxic to a range of species, persistent in the environment and able to accumulate in biological tissues. They may create problems with residues in the cultured fish and shrimp, affect the surrounding environment, and allow antibiotic-resistant bacteria to enter the environment. Some of these bacteria may be pathogenic to marine species or even humans. In addition, the escape of farmed fish from cages may alter the genetic composition of wild stocks if they interbreed, resulting in reduced fitness of wild species. Despite development of regulations and technological improvements, the environmental and health problems of aquaculture remain significant and seem set to increase, given the continued economic pressure for growth of the aquaculture industry.