Around the world, people are eating more seafood than ever before and demand is on the rise. In order to meet this demand people are raising fish, shrimp and oysters on “farms” – a practice known as aquaculture. Today, nearly one-third of our seafood comes from these fish farms but the question remains is aquaculture sustainable?
Opinions vary, biased by agenda. Like many environmental issues, it is a complex question and the answer isn’t “black or white” but varying shades of grey. The environmental impact of aquaculture depends on many variables including types of fish raised, methods used and location. Some methods of aquaculture are environmentally sound and some are detrimental.
Proponents of aquaculture argue that the practice is rooted in ancient history and this is true. The earliest records of fish farming are from China and date back to 2500 BC. The Bible refers to fish ponds (Isaiah, Chapter 19, verse 10) as do hieroglyphics from Middle Kingdom Egypt. Romans raised fish in ponds and cultivated oysters and in Hawaii aquaculture practice is at least 1000 years old. However, the scale that aquaculture was practiced in ancient times was much smaller than today.
Although some aquaculture operations are small and provide for local consumption, many are large scale farms for international production. In 2000, aquaculture production worldwide was 45 million tons and estimated at a value of $56 billion (USD). By 2003 those numbers increased and aquaculture production was equal to a value of $67 billion (USD). It is a booming international industry born out of necessity to meet food demands of an increasing population.
The key environmental issues of aquaculture today include demand on marine resources (for feed and eggs), risk and impacts on wild fish populations and risk of aquaculture pollution on wild habitats and ecosystems. If an aquaculture practice is to be considered sustainable it must be able to maintain or increase production long-term without impacting natural resources. To understand these impacts it is important to discern different aquaculture methods.
Aquaculture has many forms: open net pens or cages, ponds, raceways, shellfish culture and re-circulating systems. Open net pens and cages contain fish in offshore coastal areas or freshwater lakes. This method is often used to raise salmon and tuna. The open net pens and cages can create several environmental problems. Farm fish can escape and overburden the local fish population’s food resource. The escaped fish can also interbreed with wild fish and compromise the natural selection process of the wild fish gene pool and take over habitats. Disease and parasites can pass from penned fish to wild fish. The antibiotics used to control these diseases pass as well releasing new strains of diseases to the wild fish population.
Ponds contain fish in a coastal or inland fresh or salt water pool. This method of aquaculture is often used to raise Shrimp, catfish and tilapia. Although the ponds are contained, this method creates wastewater. Unless treated properly, this wastewater can pollute the environment and surrounding water supplies. Shrimp ponds have a record of construction in mangrove forests, delicate coastal ecosystems that serve as maritime “nurseries.” Irresponsible construction and farming in these delicate areas has destroyed more than 3 million acres of coastal habitat worldwide. This is most prevalent in Asia and South America, tropical areas that supply shrimp to European and American markets. The practice destroys natural habitat and threatens local economies by desecrating livelihoods based on unsustainable natural resource management.
Raceways divert water from a stream or well into man-made channels where fish can be raised. This method of aquaculture is often used to raise rainbow trout because it simulates a natural river or stream. It is strictly regulated in the U.S but if practiced irresponsibly can cause problems. Like pond systems, raceways create wastewater which if left untreated can contaminate the local environment and nearby water supplies. Farmed fish also have the potential to escape burdening wild fish food resources, compromising the natural gene pool through interbreeding and spreading disease and parasites.
Shellfish culture is used to grow oysters, mussels and clams. The shellfish are suspended in water by ropes, trays or bags. Shellfish aquaculture can lead to waste accumulation if the density of cultured shellfish is too high in proportion to currents or tides. However as filter feeders, these species can help cleanse waters by clearing excess plankton. Shellfish culture depends on non-polluted water and this often initiates collaborative efforts between industry and communities to keep coastal waters clean. The biggest problem with shellfish culture is that it has a history of introducing exotic or invasive species that disrupt fragile ecosystems and can lead to extinction of native species. Overall, this form of aquaculture has little impact on the environment.
Of all the aquaculture methods, recirculating systems address the most environmental concerns associated with fish farming. This method encloses fish in tanks where wastewater is treated and recirculated. This aquaculture method is commonly used to raise striped bass, salmon and sturgeon. Fish cannot escape from the tanks to pose a threat to the local population and there is little risk of pollution from untreated wastewater. Recirculating systems are the most expensive of all aquaculture methods and require electricity to run. This form of aquaculture can also be used to raise Tilapia, a plant eating fish that is easy to farm. The least impact is from fish farms that raise omnivores or better yet vegetarian fish like Talipia or shellfish. Farms that raise carnivores like shrimp, salmon and tuna require feed from wild fish, like anchovies. To raise carnivores in fish farms creates more demand on wild fish reserves.
The need to reduce over fishing of certain fish species makes aquaculture a good alternative. The wild fish populations are no longer “endless” and many species are endangered by human consumption demands and unsustainable fishing methods. As an industry, aquaculture has the potential to provide sustainable food resources. If environmentally sound methods are practiced, aquaculture can be a non resource extractive food source. This has unlimited potential to meet worldwide demand and to alleviate hunger and poverty in rural, developing regions by providing local food security.
Over the past forty years, the industry has experienced growth that is beyond any other agri-food industry. This was fueled by increasing awareness of declines in wild fish populations. It is an industry that has grown alongside the environmental movement. That is not to say that aquaculture has an environmentally clean record but that it has experienced close scrutiny under watchful eyes.
So is the practice of aquaculture is a good idea? If practiced through sustainable methods it can provide a renewable food source and work to support restoration of wild fish stocks. It is a consumer driven industry meaning responsibility falls into the hands of the private sector as well as industry and government. The best way to ensure that aquaculture evolves along a sustainable path is to make sustainable consumer choices and continue with a collective watchful eye.