Environmental Problems of AquaculturePaul Greenberg | 18 April 2014
In food systems, nothing comes for free. All attempts at increasing human food supplies inevitably produce environmental consequences elsewhere. With aquaculture, those consequences are only now starting to be understood. Reporters looking to cover the aquaculture sector should be well versed in the environmental factors of aquaculture. Some of the key environmental factors are as follows:
Forage fish impacts:
Though some aquaculture species are raised on vegetarian feed, many, particularly more recently domesticated species like salmon, require wild fish rendered as fish meal and fish oil for their food. What this means is that most of the time, it takes more than a kilogram of wild fish to create a kilogram of farmed fish. This finding was most famously publicized in a 2000 paper in the journal Nature. In their report, Naylor et al. estimated that the Fish In – Fish Out ratio, or “FiFo” as the feed-to-edible product ratio is called, could be more than 3 kilograms of forage fish to produce 1 kilogram of edible farmed fish. Since their paper was published, the fish farming sector has grown more feed-efficient, but subsequent studies such as “Little Fish Big Impact” by the Lenfest Forage Fish Task Force continue to assert that the exploitation of the world’s forage fish is undermining marine food webs. Some 20 percent of the world catch is now forage fish, the vast majority of which is used for aquaculture feed.
The farming of marine fish, crustaceans and even bivalves produces waste in the form of fecal matter and unused feed. These largely nitrogen-based wastes can cause oxygen depletion in coastal environments and a net loss of marine productivity in certain coastal areas. Additionally, the use of antibiotics, antifoulants, and pesticides are all problems that aquaculture can introduce into the marine environment.
Aerial View of Shrimp Farms. By far the greatest threat to mangrove swamps comes from the rapidly expanding shrimp aquaculture, which offers a high economic return.
Of all aquaculture practices, the farming of shrimp has probably generated the most criticism. Shrimp are farmed in tropical and subtropical ponds and impoundments that are frequently sited within the confines of coastal mangrove forests. Because pollutants can accumulate in ponds over time, in the early days of shrimp culture ponds were often abandoned, only to be replaced by new ponds.
Diseases such as the bacterially-caused vibriosis and the viral “white spot” disease also led to pond abandonment. This process resulted in the destruction of hundreds of thousands of acres of mangrove forests – ecosystems critical to the production of wild fish and the protection of the coast from storm surges. Though mangrove cutting has abated in recent years in some places—most notably in Thailand where mangrove cutting is now illegal—new challenges continue to arise. In 2009, a new shrimp disease called Early Mortality Syndrome (EMS) arose in China and spread throughout Southeast Asia. In 2013, losses from EMS totaled more than $1 billion.
Until recently, many aquaculture operations have failed to adequately address the issue of escapes of farmed fish. Farmed fish and shrimp are often genetically different from fish inhabiting the adjacent environment and ecologists have expressed concern that farmed escapes are diluting wild populations’ genetics. This is particularly worrisome in salmon aquaculture where millions of fish escape every year from netcages suspended in the open ocean. Tilapia too, which are grown in freshwater ponds have a great proclivity to take over watersheds should they escape.
The farming of species in wild environments can be a vector for disease proliferation in the wild environment. Disease transfer in salmon aquaculture is perhaps the most reported instance of this phenomenon. The disease infectious salmon anemia first appeared in Chile in the 1990s and has since been noted in other environments around the world. Poor biosecurity and global transfer of salmon larvae helped speed the transfer of the disease from country to country and even continent to continent. Sea lice primarily of the genuses Lepeophtheirus and Caligus are another frequently noted aquaculture side effect. Sea lice attach themselves to the skin of their intended victim and draw nutrients from the body of their host. This is particularly damaging to salmon juveniles. Critics of aquaculture note that large farm operations established near the migration routes of wild salmon can cause sea lice to aggregate and jump from farmed animals to wild.