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Cage farming is comparatively simple to set up and maintain because there is no need for advanced water quality control systems. However, this reliance on nature for water management causes environmental problems, notably algae blooms caused by the concentrated waste and nutrients (Aquaculture: Fulfilling Its Promisefulfilling its promise, 2007). The severity of these risks depend on site selection, whether the captive population is limited to the carrying capacity of the body of water, and levels of pollution from nearby sources such as industry. Ocean waters near the shore with good tidal flushing are most suitable for this type of aquaculture, and more exposed sites and attention to cage density can prevent risks to the environment (C. Goudey, personal communication, November 20, 2007). Other strategies to lessen the risk of environmental damage use shellfish, sponges, or other filter feeders to improve water quality (Shin, 2005). Also, it may be possible to use mobile cages to reduce the effects of unhealthy waste concentration (MIT Sea Grant, 1998). The first option would work well for countries where the right species are already native to the area, while the second option would allow landlocked nations or nations with little coastline a chance to develop aquaculture, as the mobile cages could be deployed in international waters. The current economic feasibility of mobile cages is unclear. While we are not currently able to provide an answer, we believe that should sufficient commercial and governmental pressure develop, means of reducing the cost of mobile-cage aquaculture would arise. These two options should provide most nations a means of performing this type of aquaculture while preserving the environment.
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We also encourage the use of intensive, closed-loop systems for aquaculture. In these systems, almost all the water is recycled, with at most 5-10% of water being replaced each day (Changing the face of the waters). This also means that escape of genetically modified stock is much more difficult and that with careful monitoring antibiotic-resistant diseases can be contained, allowing the safe use of genetically modified fish and antibiotics. Furthermore, as the water is in a closed loop, the waste from the fish will not impact the surrounding environments. The ability to stack shallow tanks makes intensive farming particularly well suited to flat fish such as flounder (C. Goudey, Personal Communicationpersonal communication, November 20, 2007). The primary downside is the complexity of the recycling systems. However, intensive aquaculture provides an opportunity for landlocked nations to become involved, and stacking tanks allows for large numbers of fish in a single facility.
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There is a growing fear that genetically modified fish escaping from cage farms could seriously impact the surrounding environment. Aquaculture broodstock (fish selected for breeding) is often chosen to create fish with traits optimized for aquaculture. However, these traits are often less useful, if not harmful, in the natural environment. There is a fear that escaped fish from farms may displace native species, either through interbreeding or putting too much pressure on the local ecosystem (The Threats threats and Benefits benefits of G.M. Fishfish). But this claim is not well supported. Though some farmed fish may interbreed with wild fish, there is little evidence that these new genes are harmful (C. Goudey, Personal Communicationpersonal communication, November 20, 2007). However, the risk still exists, so we recommend mixing randomly selected wild fish with the broodstock, to minimize the differences between the two groups.
Great work is being done to find replacements for wild-caught fish in farm feed. According to Soy In Aquaculture "Soybean meal can replace all or most animal meals in the feeds for the majority of cultured omnivorous freshwater fish" (Quick facts). " We encourage such efforts, as they may prove key to ending aquaculture's dependence on capture fisheries. We also recommend using low trophic level farmed fish to feed higher trophic level fish.
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To solve these problems, we propose that developing countries use cage farming to raise large numbers of low trophic level fish, using plants as feed and our previous suggestions to prevent negative environmental impacts. These fish would be used both as a source of protein for locals and as food for higher trophic level fish farmed in more wealthy nations. The money from exporting fish would allow the developing countries to keep the fish farms operating, helping supply food to their citizens. In this manner, developing nations would get both food for their citizens and a new revenue stream, while developed nations could continue to consume higher trophic level fish with very little negative environmental impact. Implementing this plan would involve encouraging companies in developed countries to move to high trophic level farming and to purchase farmed feed fish from developing nations. In the United States, the National Oceanic and Atmospheric Administration (NOAA) is already authorized under the Merchant Marine Act to provide loans to help build aquaculture facilities (NOAA 10-year plan for Marine Aquaculturemarine aquaculture), which could help motivate corporations. By controlling the types of facilities it grants loans to, NOAA could encourage the creation of high trophic level farms that use only sustainable feed. We also urge the creation of an international team of aquaculture experts to assist nations with farm design and placement, ensuring the most environmentally friendly farms possible and making them even more economically feasible for developing nations.
There still remains the question of scale. Farms have produced anywhere from 63,000 to over two million pounds of tilapia per year (Sell, R., Tilapia1993). At an average per capita per year consumption of about 35 pounds, a single farm could feed as many as 50,000 people (Availability and Consumption consumption of Fishfish). This would allow the entire population of the Maldives, more than 350,000 people, (Maldives information) to be fed with as few as eight large fish farms.
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NOAA recently released a 10-year plan for aquaculture in the United States (NOAA 10-year plan for Marine Aquaculturemarine aquaculture). We agree with its goal of increased usage of farming, particularly the use of aquaculture to rebuild stocks of wild fish. As the plan seems to be focused more on production and research goals, we feel it is compatible with our plan and encourage its adoption.
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