Aquaculture Impacts on the Environment (Released December 1999 )by Craig EmersonReview Key Citations Web Sites Glossary Conferenc es Editor Review Article Whether as an economic windfall for developing countries, or as one of the most environmentally-destructive food industries, aquaculture has come under increasing scrutiny and criticism as the world tries to supply food for a population exceeding six billion. Aquaculture, the farming of aquatic organisms such as fish, molluscs , crustaceansand plants, is the fastest growing food production sector in the world 1 , but its sustainability is not assured. Pollution, destruction of sensitive coastal habitats, threats to aquatic biodiversity and significant socio-economic costs must be balanced against the substantial benefits. Aquaculture has great potential for food production and the alleviation ofpoverty for people living in coastal areas, many of who are among the poorest in the world. A balance between food security and the environmental costs of production must be attained. Aquaculture Development & TechniquesFor over 3,000 years, fish have been farmed in China, a country that continues to dominate the industry by producing 83% of the world's aquaculture output 2 . Other key producers include India (6%), Philippines (4%), Indonesia (3%), Republic of Korea (2%), and Bangladesh (1%), a list overwhelmingly concentrated in the developing world. Everything from sea cucumbers to sea horses is farmed, but the vast majority of production is carp, accounting for ~50% of aquaculture production measured as weight or value. The remaining top cultured speciesinclude kelp, oysters, shrimp and salmon. Salmon mariculture is often in the news, but the fish farming industry is concentrated inland, with over 15 million tonnes of fish produced in freshwater systems compared to 9.7 million tonnes produced at sea. The remaining 1.6 million tonnes is produced in brackishwater ponds. Seaweed farming accounts for another 7.7 million tonnes. There are a variety ofproduction systems around the world, including ponds, tanks, raceways, and cages or "netpens". There are hundreds of variations in technique, but there are only two significant differences: water processing and feeding regime. By economic necessity, most inland facilities use a flow-through system where water is diverted from surface water (lakes, rivers) or from natural underground reservoirs (aquifers). In many parts of the United States, aquaculture has been legally classified as a beneficial, nonconsumptive use of water, but in some states such as Idaho, the trout industry's raceways require huge quantities of freshwater which combine with drought to result in a drawdown of the aquifer. Recirculating systems only require periodic additions to top-up the water level, but the accompanying cost of filtration or aeration to maintain water quality restricts implementation. For cultured species held in natural water bodies, restrictions generally reflect site selection because water quality is heavily dependent on natural currents in and around the farm. Although water resource issues are significant, there is a great deal of environmental concern focused on feeding techniques. The source of food for all aquaculture species can be divided into: 1) the use of artificial feed (aquafeed) in finfish and some shellfish operations, 2) provision of natural food (e.g. phytoplankton) in shellfish operations, and 3) a combination of natural and artificial feed. Whether inland or coastal, any operation that relies on artificial feed to grow fish faces the quandary of increasing production at the expense of increasing pollution from farm effluent. Aquaculture Effluent: Pollution of Inland & Coastal WatersIn 1989, a sudden and catastrophic collapse of wild seatrout populations in areas close to salmon rearing cages in Ireland gave aquaculture critics a focus for protest. Although a link between fish farming and the decline of natural stocks cannot always be established, some environmental effects are clear. Unlike mollusc farming, many species offish depend on a diet of artificial feed in pellet form. This feed is broadcast onto the surface of the water, and is consumed by the fish as it settles through the water column. Because not all the feed is eaten, a great deal of feed can reach the bottom where it is eaten by the benthos or decomposed by microorganisms. This alteration of the
