Africa and Southeast asia lease of about 100 kg of impacts of aquaculture. Fc being cleared at an alarming nitrogenous compounds, like example, several countries rate to make room for shrimp ammonia, into nearby waters where salmon are farmed have ponds(gujja and Finger-Stich(Roth 2000: 38). Nutrient instituted controls on 1996:12-15,33-39; Iwama pollution from aquaculture, in production to ensure that 1991: 192-216) In just 6 years, turn, can cause declines in pollution is kept within from 1987 to 1993, Thailand aquaculture productivity by acceptable limitsFAO lost more than 17 percent of its promoting outbreaks of disease 1997: 22). In some cases, new mangrove forests to shrimp among the fish(Naylor et al. technology has also helped In ponds(olmes 1996: 36) 20008) Puget Sound, on the west coast Destruction of mangroves Paradoxically, some of the United States, of leaves coastal areas exposed to aquaculture production also salmon farmer is using a giant, erosion and flooding, and has puts more pressure on ocean floating, semienclosed tub to altered natural drainage fish stocks, rather than raise his fish rather than the patterns, increased salt relieving pressure. As noted usual porous pens made of intrusion. and removed a previously, carnivorous species netting. The tub prevents fish critical habitat for many aquatic like salmon and shrimp depend wastes from polluting species(Iwama 1991: 177-216). on high-protein feed ding waters and also According to one estimate, for formulated from fishmeal-a keeps fish from escaping and every kilogram of shrimp blend of sardines. anchovies intermingling with wild farmed in Thai shrimp ponds pilchard, and other low-value salmon, which would developed in mangroves, 400 g fish. But it is also becoming contaminate the gene pool of of fish and shrimp are los more common, especially in the native fish(Christensen from wild captured fisheries Asia, to boost the weights of 1997: 27-29). Integrating the aylor et al. 2000: 6) herbivorous and omnivorous production of fish and other Intensive aquaculture ish by giving them feed that marine products, like seaweed operations can also lead to contains as much as 15 percent and mussels that grow well water shortages and pollution. fish meal and fish oil. There wastewater from intensive farm requires 50-60 thousand addition of extra fish meal and nutrient and particulate load Raising 1 ton of shrimp in a are growing concerns that the farms, can also help reduce th litres of water (Anonymous oil could place significan In Chile. some salmon are 1997: 109). When that water is pressure on the pelagic farmed with a red alga that flushed from the ponds into fisheries and marine removes nitrogen and surrounding coastal or river ecosystems that supply it phosphorous wastes from the waters in exchange for fresh (Naylor et aL. 2000: 4, 8). By cages. The effluent can also be applies. its heay some estimates, as much as 33 d to produ concentrations of fish feces, percent of fishmeal is used for crop, offsetting the costs of uneaten food. and other aquaculture feeds, and it takes creating the integrated farming organic debris can lead to ughly 2 kg of fishmeal to system(Naylor 2001: 9) oxygen depletion and produce a kg of farmed fish or Even in the problematic contribute to harmful algal shrimp. The result is a net loss shrimp-farming industry, there blooms In Thailand alone of fish protein (Naylor et al. re some initial signs of hrimp ponds discharge some 2000: 4-5) progress. In South Asia,a 1.3 billion m of effluent into The Food and Agriculture major shrimp producer has coastal waters each year Organization of the United instituted a temporary ban on Holmes1996:3435).In Nations(FAO)asserts that ew ponds until the Scotland, producing a ton of some progress has been made government adopts an farmed salmon results in the in reducing the environmental acceptable social and OEarthTrends 2001 World Resources Institute. All rights reserved. Fair ed on a limited scale and for educational©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. 3 Africa and Southeast Asia being cleared at an alarming rate to make room for shrimp ponds (Gujja and Finger-Stich 1996:12-15, 33-39; Iwama 1991:192-216). In just 6 years, from 1987 to 1993, Thailand lost more than 17 percent of its mangrove forests to shrimp ponds (Holmes 1996:36). Destruction of mangroves leaves coastal areas exposed to erosion and flooding, and has altered natural drainage patterns, increased salt intrusion, and removed a critical habitat for many aquatic species (Iwama 1991:177-216). According to one estimate, for every kilogram of shrimp farmed in Thai shrimp ponds developed in mangroves, 400 g of fish and shrimp are lost from wild captured fisheries (Naylor et al. 2000:6). Intensive aquaculture operations can also lead to water shortages and pollution. Raising 1 ton of shrimp in a farm requires 50-60 thousand litres of water (Anonymous 1997:109). When that water is flushed from the ponds into surrounding coastal or river waters in exchange for fresh supplies, its heavy concentrations of fish feces, uneaten food, and other organic debris can lead to oxygen depletion and contribute to harmful algal blooms. In Thailand alone, shrimp ponds discharge some 1.3 billion m³ of effluent into coastal waters each year (Holmes 1996:34-35). In Scotland, producing a ton of farmed salmon results in the release of about 100 kg of nitrogenous compounds, like ammonia, into nearby waters (Roth 2000:38). Nutrient pollution from aquaculture, in turn, can cause declines in aquaculture productivity by promoting outbreaks of disease among the fish (Naylor et al. 2000:8). Paradoxically, some aquaculture production also puts more pressure on ocean fish stocks, rather than relieving pressure. As noted previously, carnivorous species like salmon and shrimp depend on high-protein feed formulated from fishmeal—a blend of sardines, anchovies, pilchard, and other low-value fish. But it is also becoming more common, especially in Asia, to boost the weights of herbivorous and omnivorous fish by giving them feed that contains as much as 15 percent fish meal and fish oil. There are growing concerns that the addition of extra fish meal and oil could place significant pressure on the pelagic fisheries and marine ecosystems that supply it (Naylor et al. 2000:4, 8). By some estimates, as much as 33 percent of fishmeal is used for aquaculture feeds, and it takes roughly 2 kg of fishmeal to produce a kg of farmed fish or shrimp. The result is a net loss of fish protein (Naylor et al. 2000:4-5). The Food and Agriculture Organization of the United Nations (FAO) asserts that some progress has been made in reducing the environmental impacts of aquaculture. For example, several countries where salmon are farmed have instituted controls on production to ensure that pollution is kept within acceptable limits (FAO 1997:22). In some cases, new technology has also helped. In Puget Sound, on the west coast of the United States, one salmon farmer is using a giant, floating, semienclosed tub to raise his fish rather than the usual porous pens made of netting. The tub prevents fish wastes from polluting surrounding waters and also keeps fish from escaping and intermingling with wild salmon, which would contaminate the gene pool of the native fish (Christensen 1997:27-29). Integrating the production of fish and other marine products, like seaweed and mussels that grow well in wastewater from intensive farms, can also help reduce the nutrient and particulate loads. In Chile, some salmon are farmed with a red alga that removes nitrogen and phosphorous wastes from the cages. The effluent can also be used to produce a seaweed crop, offsetting the costs of creating the integrated farming system (Naylor 2001:9). Even in the problematic shrimp-farming industry, there are some initial signs of progress. In South Asia, a major shrimp producer has instituted a temporary ban on new ponds until the government adopts an acceptable social and