What is aquaculture?
Aquaculture, sometimes referred to as fish farming or seafood farming is the creation of various systems by humans to produce seafood for consumption, usually at a large scale. These systems allow conditions to be controlled and allow for a much more certain production than traditional wild fishing techniques.
Many types of seafood are farmed around the world today from large fish such as salmon to shrimps, oysters and even seaweeds.
The global aquaculture industry is growing rapidly, growing at a rate of 8.3% per year between 1970 and 2008 which is much higher than 2.9% growth in the livestock industry. The industry is now valued at 85 billion dollars. (1)
With a growing demand for fish, aquaculture will become the dominant method of production, for this reason, it is important to closely look at the sustainability of the technology and look for solutions to any issues as early as possible.
The industrialization of aquaculture
Aquaculture is a tradition that dates back a long way, with traditional methods far removed from what you see today. The earliest known record of humans using this method of fish farming is of indigenous Australian’s raising eels over 8000 years ago.
Over the following few thousand years, various cultures across the world used a variety of methods to start farming fish, from bamboo cages in southeast Asia to man-made fish ponds in Hawaii around 1000 years ago.
Only in the past few decades has this been scaled up to industrial levels in a similar way to other agriculture, with pelleted food and the addition of hormones, steroids and even genetic modification.
The different methods of aquaculture
Before heading onto the impacts it is important to note that aquaculture comes in several forms and the environmental impacts vary depending on which method you assess. Here are the most common systems used around the world today:
In a flow-through system, fish species such as trout and bass are kept in a series of tanks on-land. Because these species live in flowing rivers in the wild, freshwater is constantly pumped in and out between these tanks to create the effect of flowing water.
Freshwater is taken usually from a nearby river, flows round all the tanks and then enters back into the river, usually after passing through a filtration system. This constant flow maintains higher water quality and higher levels of oxygen in the tanks.
Open cage systems (Mariculture)
Open systems are situated within the natural environment, usually in coastal areas. Fish are kept in cages which are suspended in the water, so natural seawater can flow in and out.
As we will come onto in this article, the open nature of these systems is what leads to many of the environmental issues. This is because all that lies between the farmed fish and the natural environment is a thin cage or net. Waste produced from the fish, along with uneaten food and anything else added to the cages can freely flow into the ocean.
These systems range massively in size from small bamboo cages in southeast Asia to giant salmon farms situated in the fjords of Norway.
In many countries, seafood such as tilapia and shrimp are farmed in ponds. These ponds are often located in coastal areas sometimes at the expense of mangrove forests. Situating them here allows the tides to create a natural flow of water and the addition of new organisms for shrimp to feed on.
More advanced farms use pumped systems rather than relying on the tides. Aeration is often required to add more oxygen to the water.
Flowing water is diverted from natural watercourses to produce a new controlled ‘raceway’. These systems are used for raising species such as rainbow trout.
A common method of growing shellfish such as oysters, clams and mussels is by suspending them in open water on ropes or in mesh bags.
As these species filter feed and as long as water is clean and has a flow can survive without any artificial inputs.
Due to a severe decline in wild populations, abalone farming has become a booming industry. In order to produce it artificial reefs are created using a large number of concrete blocks. The abalone feed on seaweed.
Where is this occurring
Aquaculture is present across the globe, however, 90% of aquaculture occurs in Asia with 60% of the total being in China alone. (FAO 2013). Fish has been the major source of protein in China since 1985.
Negative Environmental Impacts of Aquaculture
This is one of the most frequently talked about impacts of open water aquaculture. Nutrients build up in the environment surrounding the fish because there is nothing to prevent dead fish, food that isn’t eaten and feces entering the water column from the cages.
These additional nutrients cause algal blooms as the tiny plants make use of all the additional nutrients.
Studies have been done into the amount of organic matter, nitrogen and phosphorus discharged into the environment from shrimp farms. Estimates showed 5.5 million tons of organic matter, 360,000 tons of nitrogen and 125,000 tons of phosphorus. Bearing in mind shrimp farming makes up only 8% of aquaculture output globally the impact across all species is assumed to be much higher. Some of the toxic chemicals that build up in these areas such as nitrogen are toxic to many sea creatures too. (1)
Transmission of disease
Having a large number of fish kept closely together in a small area means that any diseases or parasites are likely to spread much more quickly.
Sea lice are one of these parasites causing big problems in aquaculture and because the cages are open systems there is the possibility that these lice could transfer to wild fish that pass by.
This risk is higher for migrating species such as salmon which may swim past multiple cages in a Fjord system when moving from one area to another.
Various drugs are used in aquaculture to prevent disease outbreaks, increase growth and prevent parasites.
In some areas such as the United States, the use of antibiotics in aquaculture has virtually ceased due to the development of vaccinations for farmed fish. But antibiotics are still used around the world.
When these antibiotics enter the natural environment they can either have direct impacts on sea life or can cause resistance to develop which can be problematic further down the line.
Energy Usage in Feed Production
To produce large amounts of farmed fish such as salmon requires large amounts of fishmeal. Fishmeal is the fish feed which is usually made from lots of smaller fish.
There is the energy input required to produce this protein in the first place. Not only that, but these smaller fish are often caught in the wild from over-exploited fisheries, negating some of the environmental benefits seen from aquaculture.
The production of feed has increased dramatically in line with the increase in aquaculture. Production went from 7.6 million tonnes in 1995 to 27.1 million tonnes in 2007, a 3 fold increase in 12 years. (2)
Use of freshwater resources
Some aquaculture facilities and hatcheries are on land. This does counter some of the concerns of housing these large numbers of fish in cages within a natural ecosystem. However, to run these facilities large amounts of freshwater are needed which have to be pumped in. Huge amounts of energy are required to pump the water and to clean and filter it.
Destruction of mangrove forests
Aquaculture has been blamed for the destruction of millions of hectares of mangrove forests in countries such as Equador, Madagascar, Thailand and Indonesia. In Thailand this is mainly for conversion to shrimp farms where cover of mangrove forests has more than halved since 1975. (3)
This has big environmental consequences. Mangrove forests provide nutrients and shelter for many fish species that breed and rear young, as well as providing habitat for many other animals such as birds, reptiles and amphibians. They also provide benefits to human coastal populations by acting as a physical barrier to coastal erosion and storm damage.
This is the destruction of vital trees that are particularly good at absorbing carbon dioxide (CO2) and so has implications for climate change too. With one study estimating that just a pound of shrimp produced in these areas adds one ton of CO2 to the atmosphere, more than ten times the equivalent of beef on rainforest cleared land.
These farms quickly become inviable, sometimes as quickly as 10 years after opening due to sludge build-up. They are mostly abandoned, leaving behind soils that are highly acidic and contaminated and can’t be used for anything else.
Acidification of soils
If a farm is land based and has to be abandoned for any reason this can leave the soils eroded and too salty to be used for other forms of farming in the future. (4)
Pollution of drinking water
Inland aquaculture has been linked to the pollution of water bodies used for human drinking water. One such study estimated that one farm producing 3 tonnes of freshwater fish would generate the equivalent waste of 240 people. (5)
Introduction of Invasive Species
There have been a total of 25 million reported fish escapes worldwide, usually as a result of damaged netting, which occurs in severe storms or hurricanes.
Escaped fish have the potential to affect wild fish populations by outcompeting them for food and other resources. This not only directly affects wild fish populations but also forces local fisherman in the area affected to fish in other areas which might already be overexploited. (6)
There is also the worry that these escaped fish could mate with wild fish and have a negative impact on the species as a whole. This is to do with the effects it has on the gene pool. The gene pool is the variation in all the genes between different fish that might account for various things such as their size or density of muscle. A large gene pool consisting of fish with lots of variation is a positive thing in a population and increases the chances of survival. When the farmed fish enter the system that have been bred to be larger and more muscular in most cases, the genes are likely to become dominant in the population, causing the gene pool to shrink impacting the survival rate.
This impact is not just a theory and has been observed already in some wild populations. In Norway, Atlantic salmon have been known to escape and breed with native populations. (7)
The same phenomenon has also been observed in the Gulf of Maine and the Rocky Mountains with farmed species even breeding with fish from similar but different species too.
This is a hard impact to police and it is difficult to create a drive for improvements within the industry. The main impacts of escaped fish are on the commercial fishing industry and conservation rather than on aquaculture. Whilst they loose some profit from the escaped fish the impacts on wild fish will not impact the fish farmers. In fact, if it affects the numbers of wild fish, it will increase the cost of that product and drive up the demand for fish produced by aquaculture.
The likelihood of fish escaping a farm and entering the natural ecosystems varies depending on the location. Some farms are monitored closely by underwater cameras, and are regularly checked by divers for any potential gaps in the cages. Some fish have also been genetically modified so that the females are sterile, meaning if they do happen to escape there is no chance of them breeding with wild fish and affecting the gene pool.
Disturbance of other wildlife
In an attempt to deter seals, which can cause damage to underwater netting, acoustic deterrents have been deployed in some cases. These devices are thought to have unintended negative impacts on whale and dolphin populations over a wider area due to their sensitivity to acoustic noise over a larger distance.
Positive Environmental Impacts of Aquaculture
Aquaculture can have some positive impacts for the environment, especially when carried out in a sustainable and well-regulated fashion.
Reduces the pressure on wild fisheries
Overfishing is a big environmental problem, driven by a growing global desire for fish. According to the Food and Agriculture Organization (FAO) over 70% of the worlds wild fish species are either fully exploited or depleted. This disrupts ecosystems, taking away predators or prey species from the oceans.
Other problems from industrial scale sea fishing include:
- bycatch where large nets are cast catching unwanted species which are simply discarded;
- injuring and deaths of wildlife caught in discarded fishing nets and lines (sometimes known as ghost fishing);
- trawling of nets along the sea bed causing damage and stirring up sediments.
Considering approximately 1 billion people on earth look to fish as a primary source of protein (World Health Organization), aquaculture reduces the drive for wild fish and the overexploitation of this highly vulnerable resource.
Although bad practices do occur it is easier to monitor the impacts of aquaculture than it is to monitor fishing in the vast open oceans.
More efficient to produce than other farmed proteins
When looking from an energy efficiency point of view, and thus carbon emissions point of view, producing protein from aquaculture is much more efficient than many other forms of protein production.
This is referred to as the ‘feed conversion ratio’ (FCR) and measures the amount of feed input required compared to the weight gained by the animal. This ratio for beef ranges between 6:1 and 10:1, meaning you need up to ten times the amount of feed to produce the equivalent amount of beef. The figure is lower for pigs (2.7:1 – 5:1) and chickens (1.7:1 – 2:1). For farmed fish though, this ratio is often at 1:1 due to their cold-blooded nature they tend to be more efficient than many warm-blooded alternatives.
These figures have been called into question in some studies and depending on the species, the ratio does creep up to a similar range of chickens, and some argue we should look at ‘calorie retention’ rather than FCR.(8) It appears fish are more efficient to produce than beef, but studies are ongoing as to just how much more.
On top of this results of a study looking at full life cycle carbon emissions of farmed fish (taking into account land-use changes) was 5.07kg of CO2 per g of trout compared to 18kg CO2 per kg for beef.
Certain farming methods have even greater positive impacts
Aquaculture extends outside of just fish and prawns and includes seaweed and similar products such as kelp.
The environmental benefits of growing these include:
- they require no fertiliser or pesticide inputs which makes them better than many land-based crops
- they require much less land
- can be harvested up to 6 times a year
- act as a carbon sink absorbing CO2
- can be used as animal feed, reducing need to grow feed on land
Similar benefits can be seen with growing shellfish such as oysters, mussels and clams too. Oysters, for example, can filter 100 gallons of seawater a day improving water quality and removing particulates and nitrogen. Oyster beds also create an ecosystem for other sealife to use as a food source or as protection.
The Tricky Problem
The environmental issues around aquaculture must be taken seriously but it is of course one of those tricky problems because it has so many benefits too.
Seafood produced in this way accounts for 15 to 20% of the protein consumption of 2.9 billion people worldwide. (9)
Fish produced through aquaculture is typically a much cheaper source of protein than others, as well as containing important vitamins and minerals. When produced and eaten locally it improves food security in an area and a source of employment and income for the local community.
The key is to try and keep these farms local, providing jobs and food for local people, as opposed to large industrial scale farms which are more environmentally problematic and don’t benefit poorer communities.
Solutions will come in a variety of ways. Technology should allow more efficient production of fish in this way and should lead to less waste entering ecosystems and less fish escaping.
There are also many common sense solutions to many of the issues mentioned. These might include:
- choosing the right site and making sure it is assessed correctly;
- using native species to minimise impacts of escaped fish;
- keeping farms local and smaller;
- not overstocking to minimise waste;
- improvement of feed quality (i.e feed that doesn’t disintegrate as quickly);
- better management of waste, using techniques such as settling lagoons or treatment tanks;
- certification and legislation around sustainability.
Some methods of farming can actually have many positives. As mentioned already, farming of seaweeds and shellfish can have huge benefits of land-based alternatives. GreenWave is an example of such an initiative that is promoting the use of green vertical ocean farming. You can listen to my podcast interview with the founder to find out more about this exciting idea below:
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- Tacon, A.G.J.; Hasan, M.R.; Metian, M., 2011. Demand and supply of feed ingredients for farmed fish and crustaceans: trends and prospects.. FAO Fisheries and Aquaculture Technical Paper No. 564. FAO, 2011. 87 pp.
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- J. A. Rodríguez-Valencia, D. Crespo, and M. López-Camacho, “La camaronicultura y la sustentabilidad del Golfo de California,” 2010
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- (Naylor, R., Hindar, K., Fleming, I.A., Goldburg, S., Williams, S., Volpe, J., Whoriskey, F., Eagle, J, Kelso, D., . . Mangel, M. (2005). Fugitive salmon: Assessing the risks of escaped fish from net-pen aquaculture. Bioscience, 55(5), 427-437. DOI: 10.1641/0006-3568(2005)055[0427:FSATRO]2.0.CO;2)
- Simms, E. L., McDowell, C., & Graham, W. (2016). Into the wild: When farmed salmon interbreed with their wild cousins).
- Fry, J.P., Mailloux, N.A., Love, D.C., Milli, M.C. and Cao, L., 2018. Feed conversion efficiency in aquaculture: do we measure it correctly?. Environmental Research Letters, 13(2), p.024017
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