|An offshore aquaculture farm raises threadfish, or moi, in a netpen (NOAA).|
Open sea aquaculture also produces much higher than normal fish waste concentrations. The waste collects on the ocean bottom, damaging or destroying bottom-dwelling life. This waste can also decrease dissolved oxygen levels in the water column, putting further pressure on wild animals. Cultivators also treat their animals with antibiotics to prevent disease. This can accelerate the evolution of bacterial resistance which can lead to great harm outside of the farm.
Additionally, fish often escape from coastal pens, where they can interbreed with their wild counterparts, diluting wild genetic stocks.Escaped fish can also become invasive, outcompeting native species.
Aquaculture is becoming a significant threat to coastal ecosystems around the world. About 20 percent of mangrove forests have been destroyed since 1980, partly due to shrimp farming. Large scale conversions of mangroves into brackish shrimp ponds have been characterized as the marine equivalent of "slash-and-burn" farming. An extended cost–benefit analysis of the total economic value of shrimp aquaculture built on mangrove ecosystems found that the external costs were much higher than the external benefits. In fact, in Indonesia, most of these farms are abandoned within a decade because of the toxin build-up and nutrient loss.
The farming of salmon also leads to a high demand for wild forage fish. Fish do not actually produce omega-3 fatty acids, but instead accumulate them from either consuming microalgae that produce these fatty acids, as is the case with forage fish like herring and sardines, or, as is the case with fatty predatory fish, like salmon, by eating prey fish that have accumulated omega-3 fatty acids from microalgae. To satisfy this requirement, more than 50 percent of the world fish oil production is fed to farmed salmon. In addition, as carnivores, salmon require large nutritional intakes of protein, protein which is often supplied to them in the form of forage fish.
Consequently, farmed salmon consume more wild fish than they generate as a final product. To produce one pound of farmed salmon, products from several pounds of wild fish are fed to them. As the salmon farming industry expands, it requires more wild forage fish for feed, at a time when seventy five percent of the worlds monitored fisheries are already near to or have exceeded their maximum sustainable yield. The industrial scale extraction of wild forage fish for salmon farming then impacts the survivability of the wild predator fish who rely on them for food.
Many members of the Florida Legislature, Congress, and the governor have been looking at aquaculture in the Gulf of Mexico as a means of supplementing the fishing industry. Unfortunately, rather than spend money on research and restoration of natural habitats, such as seagrasses and natural reefs, our representatives have seen selling our seas to big corporate interests as a viable option. Letting this happen could spell disaster for natural fisheries and would certainly be bad not only for our environment, but for small fishing operations as well. Please stand with us and let your representatives know today that you oppose giant factory farming operations in the Gulf and that you want then to focus on protection and restoration of natural fisheries instead.
"History of Aquaculture" Food and Agriculture Organization, United Nations.
FAO (2006) The State of World Fisheries and Aquaculture (SOPHIA)