Local, Small-Scale Polyculture: Solving the Problem of Uncertainty for American Consumers


Figure 1. Example of aquaculture. Andy Danylchuk, powerpoint: Aquaculture 2012

Katelyn Buckley, Environmental Science and Hillary Whitcomb, Natural Resource Conservation

Introduction to Aquaculture

Agriculture, “possibly the greatest single milestone in man’s history” (Baker, 2013), is credited with starting human civilizations. The domestication of plants around 5-6000 years ago allowed tribes to settle down and provide a reliable source of food, often in surplus. This surplus of food jump-started a population increase, that in turn pushed for more technological advancements in the field that would further increase yields (Baker, 2013). Agriculture is a primary reason why humans have become the dominate species on the planet, and the domestication of food resources did not stop with terrestrial plants. Sometime between the years 2000-1000 B.C.  a Chinese man named S. Y. Lin was the first known person to farm raise the common carp (Cyprinus carpio) in captivity. It was in China, almost 4000 years ago, that aquaculture first appeared (Rabanal, 1988, p. 4). As with the agricultural revolution, aquaculture provides a significant source of protein that, in this day and age, can be transported and enjoyed by people around the globe.

The United Nations Food and Agriculture Organization (FAO) defines Aquaculture as:

farming of aquatic organisms including fish, molluscs, crustaceans and aquatic plants. Farming implies some sort of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc. Farming also implies individual or corporate ownership of the stock being cultivated… (FAO, 2002).

In total, 600 aquatic fish species are farmed worldwide are used for food and non-food uses (FAO, 2012, p. 26). An aquaculture farm can exclusively raise one aquatic species, known as monoculture (Figure 1). These farms often raise higher order species such as Bluefin Tuna, or Salmon (Figure 2). Some farms cultivate multiple aquatic species including plants, this is known as polyculture. Polyculture systems are ideal in terms of efficiency, by taking advantage of ecosystem services such as primary production and filtration of contaminants (Figure 4).

Aquaculture in the twenty-first century is a complex industry, that helps satisfy the wants and needs of a growing world population. It accounts for 30% of all fish consumed (White et al., 2004, p. 5), and provides a necessary source of protein for people all over the world. In the last thirty years the aquaculture industry worldwide expanded by almost 12 times, with an average annual growth rate of 8.8% (FAO, 2012, p. 25) (Figure 6). This expansion coincided with a significant jump in the global population size, thus providing necessary sources of food for both developed and developing countries.

The Problem of Unknowns

The United States of America relies heavily on imported fish to meet the demands of the people. In total 91% of the fish consumed in the states is imported, 50% of that comes from aquaculture (NOAA, 2013) (Figure 5). As our population grows, the demand for this healthy source of protein rises, consequently causing the total amount of imports to increase. From 1990 to 2010, the total production of farmed fish in the United States decreased from 54.8%-37.9% and is currently not expanding, however the demand for fish increases with the population size (FAO, 2012, p. 43).

A major problem associated with the aquaculture industry is the presence of unknowns surrounding the production of imports. Being a country that consumes a large amount of imported farm-raised fish makes us vulnerable to the consequences of poor management practices. It is important to note that 30% of the 190 countries that practice aquaculture do not report on their production, culture environment, farming methods or the facilities. 40% do not provide complete data with poor quality and time delays (FAO, 2012, p. 43). Vital information pertaining to the production process is often left out of these incomplete reports. If these countries do not feel responsible for reporting their production and methods, it is likely they will not have proper management practices in place to protect the quality of the product or the surroundings. As consumers we do not have access to the information necessary to make informed decisions about what we eat, thus providing no incentive for the aquaculture industry to become more sustainable (Figure 3). It is also very unlikely that entire countries will change their ways in order to please the American consumers.

Importance of Consumer Selectivity

There are many reasons why individual American consumers should be selective about what they eat. Many would agree that we have a moral obligation to ourselves and our surroundings when it comes to the exploitation of a natural resource. Consider this statement by Anna Lappe, “Every time you spend money, you’re casting a vote for the kind of world you want.” We have the capability to shift our buying power towards systems that are worth supporting, such as sustainable aquaculture. Meaning these systems are environmentally sound, economically profitable, socially acceptable by supporting community development and can be sustained at the same level of production for generations (White et al, 2004). Virtually all the current systems are not sustainable. They contribute to environmental pollution, degradation of wild fish stocks, the current practices take away from future yields and increase future costs. They are also run by a select few hundreds of miles away when they could be providing more jobs for the growing population here in America.

Joblessness is a huge issue in the United States today. Foreign trade is an important aspect of American culture, but when few citizens actually benefit it becomes more detrimental for the economy and society. Not to mention, America’s growing reliance on imported farmed fish from large-scale sources increases the dependence on non-renewable resources, that further depletes these resources and contributes to environmental degradation. China, being the primary contributor for America’s fish consumption, requires significant resources to transport the product and costs continue to rise.

On a smaller scale, the consequences of poor management practices can directly affect our health. All aquatic species in highly developed areas, wild or farmed, are subject to frequent and intense toxic inputs, that negatively impacts the individual and community health. The growing population increases the effluent discharge into the aquatic environment (Wurts, 2000, p. 143), which continuously decreases the quality and quantity of fish stocks.

Additionally, disease such as bacterial, viral and parasitic infections can spread rapidly in a culture environment due to high density and neglect; this also decreases the quality and quantity of the fish stocks, which in turn affects our diets (Barnes and Mann, 1991, p. 260) (Figure 7). Another concern is the bioaccumulation of heavy metals such as mercury. Higher levels are in higher trophic level fish such as the widely consumed tuna and swordfish. The mercury levels in individual fish do not breakdown, rather they accumulate especially in those top predators. Mercury is poisonous and dangerous especially for children and pregnant women, as exposure can damage the brain, heart, kidneys, lungs and immune system (MedicineNet.com, 2013).

Solutions for Sustainability

With all of this in mind, the growing importance of farmed fish in American diets results in increased imports of questionably raised fish, thus the shift towards local, small-scale polyculture systems will remove uncertainty and improve environmental, economic and sociological conditions. Polyculture systems of aquaculture have been used throughout the world for long periods of time, allowing us to observe and compare the systems. Not only will polyculture systems reduce the strain on wild fish stocks, they will create a more sustainable industry.

Proposal: Power of the Public

               The consumer has the ability to change the system by shifting buying power. We propose we use this power to push for local, small-scale polyculture systems that are beneficial for the people and the environment. However, this shift cannot happen overnight and requires steps to help the public and economy easily transition to the sustainable systems in America. Currently, there are campaigns to shift the buying power of the public towards sustainable products. These include certification, eco-labeling and awareness programs. Cooke, Murchie and Danylchuk (2011) discuss that the public is generally unaware of the state of inland fisheries and the surrounding environments. They suggest simply informing the public of the problem, so “they will be motivated to act through their purchasing power” (p. 915). Consumers must use all available information to make informed decisions on buying imported fish by following those that actually report on their production and methods. However, Naylor (2000) states that “at the same time, the private sector must alter its course and recognize that current practices that lead to dependence on pelagic fisheries habitat destruction, water pollution and non-native introductions run counter to the industries long term health” (p.1023). This is very unlikely, without push from the public.

The aquaculture industry can only exist if there is demand from consumers. Therefore, if America as a country were to stop consuming imported farmed fish, the industry would either have to find a new market or shut down production. It is possible to create a new market based on the values of the consumers. If consumers were only interested in buying eco-friendly products, the aquaculture industry would be forced to make a shift towards eco-friendly production. After making consumer values clear, it is now possible to turn our attention to investors and push for government support of polyculture construction in the United States.

Why Local, Small-Scale Polyculture?

Ecosystem Services Increase Efficiency

Often, the chosen species in monoculture systems is a high trophic level species that takes in more biomass than it yields, this is due to the decrease in energy as it moves up the food chain, so energy conversion is not 100% efficient (Barnes & Mann, 1991, p. 260) The inefficiencies of energy conversion rates between trophic levels causes this net loss, as 10% of biomass is lost as energy moves up from primary producers to first, second and third level consumers (fig. 2).

Polyculture systems are beneficial because they increase the efficiency of the system by using ecosystem services. Some species that are integrated into polyculture systems are usually filter feeders or bottom feeders, like carp or mussels. This means they are more likely to utilize all the provided food. In a study analyzing the effects of aquaculture on world fish supplies, the authors explain that some herbivorous species of fish, or bottom feeders, require less fish as inputs than what is ultimately harvested (Naylor et al., 2000). “In contrast, carnivorous species require 2.5-5 times as much fish biomass” compared to total net biomass production (Naylor et al., 2000, p. 1019). For example, a family could consume 1lb. of salmon or 2.5-5 lbs. of the carp that it would take to produce that 1lb. of salmon (it’s just not as tasty). This shows that utilizing herbivorous species in addition to the other target species of fish, you may increase the productivity and could actually cause a net increase of fish production.

In addition to lower trophic level species, plants provide a variety of ecosystem services that contribute to overall efficiency. For example, “[b]y integrating fed aquaculture (finfish, shrimp) with inorganic and organic extractive aquaculture (seaweed and shellfish) the wastes of one resources user becomes a resource (fertilizer or food) for the others” (Chopin et al., 2001, p. 975). Including seaweed into the aquaculture system promotes the balanced ecosystem approach, and can provide nutrient bioremediation to the effluents before they are discharged, and benefits to the cultured organisms (Chopin et al., 2001). Replicating the aquaculture system to be more like a functioning ecosystem has benefits because most of the work is done by the ecosystem, leaving less work to be done by the fish farmers. Therefore, polyculture implementation is perfect for utilizing the advantages of ecosystem services.

Environmental Impacts

The shift towards efficient polyculture systems provides access to more variety of fish meat. Rather than focusing only on higher trophic level species, which are more costly to produce, the system raises species that rely mainly on natural primary production. In this system less fishmeal is needed. This decreases the stress on wild fish stocks, that make up 75% of the feed used. The reduction of intake from wild stocks allows populations to rebuild including the predatory species. This also increases marine biodiversity.

The filtering of contaminants by consumers decreases the effluent discharge into the environment. For example, many salmon farms are a major source of eutrophication in coastal regions (Whitmarsh, Cook, & Black, 2006). Eutrophication is the result of an increase in vegetative or algal cover caused by effluent discharge and nutrient loading. It consumes most if not all the available dissolved oxygen and can kill entire aquatic ecosystems. It is important to keep the those populations in check, to ensure that their oxygen consumption at night or during decomposition is not greater than the rate of replacement (Wurts, 2000, p. 146). In the research study done by Whitmarsh et al. (2006), they prove that integration of mussel lines into a salmon farm could help by removing a large amount of the effluent discharge that is produced by the fish (Figure 9). The reduction in organic waste helps offset the risks of eutrophication. This increases the health of the surrounding environment.

In addition, the filter feeders reduce contamination within the culture environment and therefore the risks of disease. Many filter feeders can actually take this waste from fish and turn it into food. Filter feeders can be an essential organism because they not only filter other wastes, but they can filter their own waste, therefore even further reducing the presence of contaminants into the culture environment (Whitmarsh et al., 2006).

Localized, Small Scale Aquaculture

In addition to considering environmental impacts, there needs to be an understanding of economic and sociological impacts as well. By transitioning to small-scale polyculture systems, the global aquaculture market will benefit and become more sustainable (Wurts, 2000, p. 145). Wurts goes on to explain, “small-scale and intermediate size farms and businesses owned by multiple independent operators would promote greater self sufficiency and provide a higher standard of living overall”  Not to mention that small-scale farms increase jobs and can be placed in close proximity to the markets; they will also “promote greater self-sufficiency and provide a higher standard of living overall” (Wurts, 2000, p.142). In addition, the quality of the product increases as time of transport decreases, further contributing to the welfare of an individual American consumer.

Centralized distribution methods are how some of our market systems in the U.S. are functioning. This means that the fish is produced in one location and dispersed throughout the country. Although this seems like an effective method, these centralized systems are heavily stocked with fish, resulting in less room and requires more aeration throughout the season (Wurts, 2000, p. 144) (Figure 8). Doing this actually can increase electricity costs to the producers.

On top of electricity costs, there is the added cost to distribute as well. Diesel fuel and gasoline can be expensive, and if those prices were to increase, it would be detrimental to the distribution to nation-wide markets making it more costly (Wurts, 2000, p. 144). Although people usually tend to not like the idea of small-scale farms, they are used widely in developing countries where they cannot afford to construct large roads to transport their fish to far locations. In small scale farms, Wurts (2000) explains how “[a]n industry could be composed of multiple owner-operators with limited to moderate acreage, at short distances from their available markets” (p. 145). Therefore, if producers wanted to distribute, they wouldn’t have to waste money on fuel to transport their fish to far away markets. Placement of these small-scale farms could be located on the perimeter of the markets, which can be dispersed throughout large geographic regions, instead of having a large industry placed in the center of distribution sites (Wurts, 2000, p. 145). While fish producers believe that having a large commercial and centralized aquaculture market may benefit them, there are various costs associated with it that become unnecessary when small-scale farms are considered.

Government Influence

Right now, government subsidies and market demand forces the expansion of high-value, carnivorous species including: Bluefin Tuna, Salmon, and Shrimp (Naylor et al., 2000). If there is going to be a shift towards more sustainable and multitrophic aquaculture systems in the U.S., there needs to be more government policies that favor these smaller-scale systems. Although this seems like a simple task, it may be difficult gathering support since there may be some concerns of polyculture implementation, for example the cost to implement this may be expensive. What could be done is that the government could provide incentives to integrate polyculture techniques. This would give aquaculture companies benefits to addressing sustainability, and therefore cause an increase in the amount of companies who would integrate these practices.

As well as government incentives, there needs to be more federal support to help the research and development, and there needs to be the elimination of subsidies for ecologically unsound fish production, and enforcement of regulation to help protect coastal ecosystems from being destroyed for unsustainable fish farming practices.

Increased Yields over Sustainability:

Current Aquaculture systems rely on controversial practices that increase current yields rather than efficiency and future production. For example, it is widely accepted for aquaculture managers to directly apply fertilizers to the system and research shows this does increase yields. The fertilizers stimulate primary production, which in turn triggers a rapid increase in food supply for all levels of consumers. A documented case study lasting for three years in Great Central Lake, Canada analyzed the consequences of fertilizer application on population densities of sockeye salmon. The results indicate that massive increases in production of phytoplankton and zooplankton (5-9 times greater) contributed to a 50% increase in sockeye salmon abundance (Barnes & Mann, 1991, p. 258).

Increasing stocking densities is another accepted way for the industry to increase overall production. For Channel Catfish farmers in northwest Mississippi, increasing demand from many U.S. states requires higher yields in limited space. The immediate solution is to increase stocking densities, doing so allows farmers to provide the consumers with what they want while making few structural changes in the short term. Increased yields as a top priority results in greater income for current farmers and a good supply of catfish for consumers (Wurts, 2000, p. 144).

It makes sense for aquaculture managers to implement possibly damaging management practices that increase current yields, they need to make a living and people need to eat. However, when density is increased, oxygen is consumed at higher rates than is naturally replaced, and disease risks are higher.  Wurts (2000) argues “increased profits are not likely to come from higher stocking densities” (p. 142).

Also, by focusing on one species, the farmer has to simulate the natural environment. This can be costly for the environment and the welfare of the species. When managers dump nutrients into the aquatic system, they purposely induce eutrophication; this promotes primary production and therefore food supply of the stock (Barnes & Mann, 1991, p. 258). This requires all external costs associated with gathering nutrients, transporting and also pumping oxygen into the system to keep the fish from dying in unhealthy environmental conditions.

Tastes of the Public:

Modern Americans who consume seafood in their diets tend to prefer higher trophic level fish, like tuna or salmon. Much of the public rely on these fish to satisfy their need for omega-3 fatty acids, which these fish can have high levels of. Cod for example has a less fishy taste due to the fact that oil is exclusively stored in the liver. Lower trophic level species of fish tend to taste a bit blander, because their diet is vegetarian.

We need to understand that even though high level trophic species may be less efficient to farm, this doesn’t mean we need to give up on farming them altogether. As long as there are ways of implementing polyculture to those farms, efficiency will increase overall. Although people will still want to eat tuna and other imported types of fish, we can still try and reduce the amount of imports by increasing the aquaculture of localized species in the United States. Increasing the amount of aquaculture in the U.S., also means that we need to give support and awareness to making sure these systems can be integrated with polyculture, and managed properly.

Costs of Change

One concern of integration of polyculture systems is the cost. The initial cost to implement more technology may be overwhelming. But it is important to focus not on current production of fish, but rather the future net benefits that will come over time. Whitmarsh, Cook and Black (2006) illustrate an example of the costs to implement polyculture into a salmon farm:

The production system for mussels is based on the intensive longline culture method, in which a series of floats is connected together by horizontal lines which support a number of vertical ropes on which mussels are grown…it is assumed that a total of 16,000 m of mussel rope are installed…Growing structures (ropes, etc) and harvesting equipment…[must be] replaced every 5 or 10 years…Operating costs consist of: annual rental on shore facilities, seed collection, labour…and other costs (p. 294).

Although the initial costs seem overwhelming, the investment overall is worthwhile.

Whitmarsh, Cook and Black (2006) conclude from this study that “an integrated salmon-mussel aquaculture system is shown to produce a positive NPV [net present value] ($1.425 million) that exceeds the combined NPV of salmon monoculture ($0.922 million) and mussel monoculture ($0.353 million)” (p.295). This shows that the value of the project is more when combined into polyculture rather than having two separate monoculture systems. Whitmarsh, Cook and Black (2006) go on to explain that “under market conditions – that is, assuming that estimated revenues and costs remain constant in real terms over the time horizon of the project—investment is expected to be worthwhile” (p. 296). This study helps prove that although there can be a lot of maintenance and upkeep of certain polyculture systems, the investment is worth it in the end because the value of the system will increase with multiple species.

Conclusions: Looking to the Future

Changing the aquaculture industry in America is important now more than ever. As we know, our population is rapidly increasing at an exponential rate. A major problem associated with the population increase is the decrease in resource availability. Even with technological advances such as agriculture, aquaculture and genetically modified crops, the increasingly large human population must be fed using resources from a finite system. Not only will shifting the buying power benefit the American public but Cooke et al. (2011) states that “informed choices made by consumers could contribute to the conservation of marine biodiversity” (p. 912). If more sustainable aquaculture systems are implemented in the U.S., then there will be more certainty regarding the sources of our food. We will be able to know where our food comes from, and make informed decisions about what we eat, and how sustainable that source is.

With all the benefits in mind, it is essential that we push for the support to implement widespread use of small-scale polyculture aquaculture systems throughout the U.S. It is important to make the public aware of these issues so that they can be sure of where their fish comes from. As mentioned before, most of our fish sources comes from questionable sources, and it is impossible to be sure what those farmed fish are being fed, or how the system is being treated. This sustainable way of fish farming is essential to help improve the welfare of the environment and its residents, which also includes us. We can’t let ignorance and stubbornness ruin our planet. As our country grows, we have to grow too.


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