Humans have been fishing for at least 40,000 years, during the Paleolithic Age of prehistory. These early fishermen utilised rudimentary harpoons and stone fish hooks attached to lines. Evidence suggests that the earliest forms of fish farming occurred in China around 3,000 years ago, in the 10th Century BC. The earliest description of a farmed fish species is those of the Cyprinidae family, commonly known as carp. This controlled farming of fish and other aquatic species, such as crustaceans, molluscs, and cephalopods, is known as aquaculture. In the following, we will discuss the definition of aquaculture, the reasons for it, its advantages and disadvantages, its environmental impacts, and how it can be conducted sustainably.
What is Aquaculture? — An Analysis of Aquaculture and its Principles
As opposed to commercial fishing operations and subsistence fishing in the wild, aquaculture involves the farming of aquatic organisms (animals and plants) in a captive, controlled environment.
Marine organisms commonly farmed include fish, crustaceans, molluscs, cephalopods, seaweed, algae, phytoplankton, echinoderms (such as sea cucumbers and urchins), and even crocodilians.
Aquaculture typically involves the construction of structures, such as fish or shrimp ponds, tanks, cages, and aquaponics. Aquaculture can be divided into two kinds- intensive and extensive.
Extensive aquaculture involves aquatic organisms farmed in enclosed structures placed within natural habitats (such as along the coastline, rivers, and wetlands), with minimal human input and relying more on the surrounding environment.
Extensive aquaculture DOES NOT allow for anthropogenic control of environmental factors, such as temperature, food, and oxygen levels.
Intensive aquaculture involves the creation of artificial structures (such as ponds and tanks) on land. Intensive aquaculture involves organisms being bred and housed in artificial tanks, reliant on human input and often in high densities. Environmental factors, such as temperature, oxygen levels, and food, are controlled by humans.
Since humans control the environment, more sensitive species can be cultivated through intensive aquaculture than extensive.
Intensive aquaculture also allows for the control of breeding and genetic input. This allows for selecting beneficial traits, such as those that increase the chance of survival, increase size, and increase output.
In addition, due to the high level of control, the monitoring and control of disease are easier to implement. This is important because illness can be of more significant concern given the higher densities in many artificial tanks and ponds utilised in intensive aquaculture.
Lastly, intensive aquaculture allows for the control of nutrition and mitigation of competition, thus ensuring that resources are evenly distributed and that the fish obtain the proper nutrients for growth and survival.
The primary problem associated with intensive aquaculture is the accumulation and disposal of organic and inorganic waste products, which can lead to eutrophication.
Eutrophication occurs when there is an excess abundance of nutrients in the environment, leading to oxygen depletion (anoxia).
Since there is minimal human involvement in extensive aquaculture, tougher organisms typically respond best to extensive aquaculture.
Organisms commonly involved in extensive aquaculture include salmon, shrimp, tilapia, and tuna.
This lack of human intervention means that there is minimal control of the various environmental pressures, such as disease control, nutritional requirements, and inter- and intraspecies competition. However, being in a more natural environment means that, provided the environment is clean and healthy, disease and nutrient acquisition are less of an issue.
One of the significant problems with extensive aquaculture is the destruction of natural habitats to make fish and shrimp ponds, etc. It is also highly dependent on the health of the surrounding environment, with any changes impacting the farmed species.
If, for example, invasive species are introduced to the area, they could negatively affect extensive aquaculture operations.
The problems associated with aquaculture will be discussed in greater detail later.
At around 66 million metric tons being produced annually, China is the world's leading aquaculture producer, followed by Indonesia, India, Vietnam, and Bangladesh. Currently, more than half of all seafood production comes from aquaculture, and this number continues to grow by around 5% annually.
The forms of aquaculture that are most common vary by region. Fish farming, known as pisciculture, involves the aquaculture of freshwater, brackish, and marine species.
The most commonly farmed fish are freshwater carp species (such as Ctenopharyngodon idella and Hypophthalmichthys molitrix), tilapia (specifically Oreochromis niloticus), and salmon (specifically Salmo salar).
Shrimp farming is another common form of aquaculture, with the most significant numbers being produced in Southeast Asia (e.g., Indonesia) and Latin America. Algaculture involves the cultivation of algae and seaweed, with the most prominent producers being in Asian countries such as China, Indonesia, Malaysia, and the Philippines.
Figure 1: Shrimp ponds in Kupang Bay, West Timor, Indonesia. Source: Brandon Sideleau, own work
Reasons for Aquaculture
Like agriculture, aquaculture allows for vastly larger quantities of food resources to be produced, which can feed a much larger human population and reduce reliance on commercial fishing operations.
Over the centuries, the demand for seafood and related marine and freshwater resources has grown significantly, placing severe pressure on marine and freshwater ecosystems. Aquaculture represents a potentially more sustainable source of aquatic resources than fishing on an industrial scale.
Advantages and Disadvantages of Aquaculture
Aquaculture has numerous advantages and disadvantages, dependent on several factors. If done with careful consideration of the environmental impact, aquaculture can be an essential tool in increasing the sustainability of seafood. Still, if done improperly, it can actually damage fisheries and the surrounding habitat. The following are some of the advantages and disadvantages of aquaculture.
Advantages and Sustainable Aquaculture
Farming shellfish, in particular, can improve an aquatic environment's water quality by removing nitrogen from the ecosystem, which increases oxygen levels and reduces the risk of hazardous algal blooms.
Extensive shellfish aquaculture also provides a habitat for some fish, crustaceans, and other invertebrates, thus increasing biodiversity levels.
Since there are no trawlers or other machinery, non-target organisms, such as dolphins and sea turtles, are also less likely to be killed, as is a common problem with commercial and subsistence fishing activities.
Commercial and subsistence fishing often inadvertently results in the death of non-target species, including those threatened.
In the Indian Ocean, for example, it is estimated that around 80,000 cetaceans (dolphins, porpoises, and whales) are killed annually by commercial fishing activities. About four million have been killed since 1950. These deaths are mainly attributed to cetaceans caught in the large commercial gill nets as a "bycatch".
Subsistence fishing also frequently results in the death of non-target species, such as bycatch. Drowning in fishing nets is a significant cause of crocodilian mortality.
The longest crocodile ever measured (dead or alive) was a 6.2-metre saltwater crocodile (Crocodylus porosus) that drowned in a barramundi fishing net in the Fly River of Papua New Guinea in 1980.
Though not as destructive as industrial and commercial fishing activities, subsistence fishing can have a major localised impact on species populations, which is of particular concern to threatened species with limited distributions.
If done correctly, aquaculture can be sustainable. One of the most critical ways in which the practice can be made more sustainable is by increasing the production of fish that are lower on the food chain and decreasing the production of predatory fish, such as salmon. This would relieve pressure on wild fish populations that are used to feed carnivorous fish species.
Incentives, such as financial rewards, should be provided to local aquaculture operators to offer positive reinforcement when they meet such sustainability rewards. Strict zoning laws and habitat protection ensure that aquaculture is not overly concentrated in specific areas, such as essential mangrove habitats.
Another benefit of aquaculture is that, if low trophic level species are used, it can increase trophic level efficiency. What does this mean? Well, let's look at energy transfer through the trophic levels. The energy required to sustain organisms increases as trophic levels increase.
When a higher trophic level species (such as salmon) preys upon a lower trophic level species (such as seaweed), only around 10% of that organism's biomass is transmitted to the next level, with the remainder used up by physiological processes.
Thus, aquaculture should involve farming species at low trophic levels, which require far less energy to produce.
Disadvantages and Environmental Impacts of Aquaculture
Pollution
Aquaculture practices can produce undesirable waste products, particularly plastic. Many structures used to farm aquatic organisms are made of plastic or have plastic components that inevitably end up contributing to the severe plastic pollution problem.
In addition, the high densities of aquatic organisms produced through aquaculture mean that an unnaturally large amount of natural waste, including faeces and dead organisms, enters the surrounding ecosystem.
Mangrove Destruction
Shrimp ponds are commonly constructed in mangrove forest areas, resulting in the removal of the mangroves, which provide vital habitat for many ecologically and economically important species, as well as removing natural protection for coastal communities from tsunamis.
This is of particular concern in Indonesia, where around 269,000 hectares of mangrove swamps have been destroyed over the past 40 years to construct shrimp ponds. The Mahakam River delta, for example, has largely been converted to shrimp pond aquaculture. This has had an unexpected consequence in the form of increased human-wildlife conflict.
The loss of natural prey species and habitat, combined with the addition of a high-density, easily accessible food resource in the form of shrimp, has resulted in saltwater crocodiles entering these shrimp ponds. Inevitably, predation by crocodiles on shrimp pond workers has become an issue.
Figure 2: Mahakam River delta shrimp ponds. Source: Google Earth, own work
Damage to Wildlife Populations
While aquaculture may seem like it would only benefit wildlife by relieving pressure on wild populations, it can be detrimental for reasons you may not have considered. Some commercially critical aquatic organisms farmed, such as salmon and shrimp, are carnivorous. These predatory species require wild fish as food resources. In fact, some farmed species consume more fish than they produce, rendering the practice unsustainable and detrimental to wild fish populations.
This can also be an issue when farming larger carnivorous species.
In the massive inland Tonle Sap Lake in Cambodia, Siamese crocodiles (C. siamensis) farms are a form of extensive aquaculture, where they are kept in cages within the lake itself. These crocodiles are primarily fed wild snakes harvested from the lake's wild. This has devastated the wild snake population, with millions being harvested annually to feed captive crocodiles.
Another way aquaculture can damage wild populations is through the escape of non-native farmed species into the surrounding natural habitat. If the escaping species breeds, it could become a significant invasive population.
Animal Welfare Concerns
Given the cramped environment and high population densities, aquaculture inevitably results in reduced animal welfare.
Aquaculture can result in an increase in disease and parasitism among farmed species.
Increased intraspecies violence can also occur due to the cramped living conditions, particularly among territorial species, such as some crocodilians.
Some of these problems can be avoided by reducing captive population densities, increasing the size of the artificial habitat, and frequent cleaning (including water treatment).
Aquaculture - Key takeaways
As opposed to commercial fishing operations and subsistence fishing in the wild, aquaculture involves the farming of aquatic organisms (animals and plants) in a captive, controlled environment.
Aquatic organisms commonly farmed include fish, crustaceans, molluscs, cephalopods, seaweed, algae, phytoplankton, echinoderms (such as sea cucumbers and urchins), and even crocodilians.
Aquaculture can be divided into two kinds- intensive and extensive. Extensive aquaculture involves farming aquatic organisms in enclosed structures within a natural habitat. In contrast, intensive aquaculture creates artificial structures (such as ponds and tanks) on land.
Some positive impacts of aquaculture include less pressure on wild fish populations and the removal of nitrogen from the ecosystem.
Some negative impacts of aquaculture include pollution, habitat destruction, increased pressure on wild fish populations (when carnivorous species are farmed), and decreased animal welfare.
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