Polyculture (IMTA), a better way to produce fish


Aquaculture of the Future

Kendall Sarapas – Natural Resource Conservation Wildlife

Alexis Duda – Sustainable Food & Farming

Aaron Johnson – Building and Construction Technology

The fishing industry has been important since the dawn of mankind, being a rich and reliable food source. One of my first fishing voyages was with my grandpa on his boat in the sea. He was an avid fisherman who went fishing quite often. I caught my first salmon on his boat which made me want to explore the world of salmon. As soon as I saw the tip of the fishing pole point down towards the water I ran over. I started reeling in what felt like a ton of bricks on the other end dragging me to the side of the boat. I clenched on to that pole with all of my strength and reeled in the massive salmon very slowly. The weight of the fish on the hook squirming around below the water was a struggle for any ten year old to handle. My grandpa came running over and helped me reel in the salmon. That weekend we chopped up the salmon and cooked it for dinner. After that first salmon was caught, I needed to know more about their way of life.
I first learned that salmon negatively impact the environment, but how? They are species that just create a lot of waste ranging from feces particles to uneaten feed. Feed for salmon is ground up wild fish (NOAA Fisheries, 2012). Salmon produce a lot of feces that sink to the bottom of their pen and the build up has many negative pollutants. These wastes makes the pen have poor water quality that leads to outbreaks of pathogens and declines in farm productivity (Naylor, et al., 2000).
The buildup of uneaten feed is one of the main negative environmental impact of aquaculture. Salmon only eat so much per day and the uneaten feed sinks to the bottom of their pens. Uneaten feed produces nutrient pollution due to the high nitrogen content in their feed. This is the build up and release of dissolved nitrogen and phosphorous in the water (Society, 2012). This leads to poor water quality and can harm the salmon if not cleaned regularly.
Another example of negative impacts from salmon are their feces. Fish feces contain nutrients that can lead to pollution and salmon produce approximately 2,025 kg of organic waste per day in each pen (Chopin, 2013). A way to solve the problems with the feces would be to add mussels and sea urchins into the system. The mussels dissolve the smaller particles while the sea urchins eat the large particles.
Uneaten food and fish feces can lead to sediment pollution that negatively impact the environment in many ways such as algal blooms. The nitrogen can create algal blooms that covers a layer of the water by creating a barrier that oxygen cannot pass through which in extreme cases cause dead zones. Dead zones are areas with low-oxygen and can cause organisms to suffocate due to lack of oxygen (National Geographic, 2012). Algal blooms develop from a rapid increase in algae in an environment creating a colored scum on a layer of water not allowing light through. Algae live off nitrogen so when a bloom occurs, they thrive. Blooms are common and can kill off large populations of fish. For example, in Canada there was a series of two algal blooms that killed nearly 260 tons of salmon and other native species (Berdalet, Fleming, & Gowen, 2016).
Uneaten fish feed will always have an impact on the surrounding environment because no feeding system is 100% efficient. In most bodies of water there is a great deal of life living on the seafloor called the benthic zone. Sedimentation of fish feces under and around fish pens and cages negatively affects the benthic zone (Naylor, et al., 2000). Research in New Brunswick suggests that about 80 percent of the waste material that comes from the salmon farms settles to the bottom, with only 20 percent remaining in the water (Ogden, 2013). Solid waste can accumulate on the seafloor creating harmful pollutants like nitrogen from uneaten feed and fish excrements (Price, & Morris, 2013). This leads to aquatic plants growing at rapid speeds because they consume the nitrogen from the water. When the plants thrive, they can take sunlight away from the benthic zone leading to a decline in population in species that live on the ocean’s floor. This then throws the ecosystem off and can have a negative cascading effect on many species.
Fish farming can be extremely unsustainable when practiced wrong. We could get rid of aquaculture all together however, per the World Health Organization, more than a billion people depend on fish as their main source of animal protein. Currently there is about a 90% decline in large fish populations such as tuna, making us rely on fisheries more now than ever before(“Big-Fish Stocks Fall 90 Percent Since 1950,” 2003). 53% of fisheries are fully exploited and another 32% are overexploited because humans are fishing more than what the ocean can support (WWF) Aquaculture can be a sustainable solution to food security and the overexploitation of commercial fishing when applied correctly. When overexploitation happens to coastal areas, it not only hurts the environment but also tourism.
Tourism can be affected because some areas rely on customers paying a lot of money to take them out fishing during the busy season but with low supplies of fish, this can decrease the customers willingness to partake in fishing activities. If the customers do not use these services it can put locals without a job or unable to survive during the off season. Another negative impact would be recreational. Some areas like the Great Barrier Reef get most of their tourism through scuba diving with fish, but without the fish there is not much to look at (Anderson, 2017). Nonetheless, if the negative impacts of aquaculture like over fishing are exacerbated the tourism and recreation industry will be greatly impacted thus affecting the entire community.
Poor water quality can cause outbreaks of pathogens and declines in farm productivity (Naylor, et al., 2000). We need to care about the water quality in salmon farming or any fish farming for that matter because it is an important factor affecting the salmons performance and health. Fish are dependent on the water they live in for all of their needs.
Negative environmental impacts of salmon farms lead to feces waste and fish feed issues that cause poor water quality which can be fixed through integrated multitrophic aquaculture (IMTA). IMTA systems are a type of aquaculture that combines different species together for optimal sustainability (Greenberg, 2011). It takes species like salmon and puts them in the same pen as filter feeders like mussels who work together to make a balanced ecosystem. It is a closed system meaning that the pens are closed off from their natural habitat so wild and domestic species don’t mix (Greenberg, 2010). IMTA is a practical solution that can make the negative environmental impacts of waste produced by salmon less severe. To target all nutrient streams, there are three main trophic groups to cover. (Chopin, 2013).
The first one is dissolved inorganic nutrients that can be absorbed by extractive species, such as seaweeds and aquatic plants(Chopin,2013). Kelp is a subfamily of seaweed that is made of large seaweeds that are bound together by brown algae (Kelly, 2013). Kelp helps to absorb dissolved nutrients such as nitrogen and phosphorus (Liutkus, Robinson, Macdonald, & Reid 2012). Using kelp in an IMTA system could take away some harmful pollutants that would otherwise be released to damage the environment. They are not filters but absorbers so they are placed with other species that filter the water without as much competition between species. Another species that absorbs inorganic nutrients is seaweed. There are many types of seaweed but we are focusing on green seaweed, the kind that you can find at most beaches on the east coast of North America. This type of seaweed is a fast growing and easy to grow plant, making it perfect for an IMTA system. These two species not only dissolve inorganic nutrients but also produce more oxygen making them great for animals that produce a lot of waste. They take the impurities out of the water and replace it with what the salmon need to survive. These species natural ability to recycle the nutrients and wastes that are present can help to improve the environmental performance of salmon farming (Government of Canada, Fisheries and Oceans Canada, Communications Branch, 2013).Seaweed and kelp can only help an IMTA system with dissolved inorganic nutrients so other species like blue mussels can help with particles.
The second main trophic group is slow sinking organic particles that generate from feed waste or feces and can be captured by organic extractive feeders, such as oysters and mussels(Chopin,2013). Mussels retain smaller salmon feed and fecal particles from the water leading to cleaner water quality. Mussels are bottom feeders that love to filter fish waste. A study shows that mussels can absorb up to 86% of feces from the salmon while another study shows 90 % absorption efficiency of feed waste from salmon (Liutkus, Robinson, Macdonald, & Reid 2012). This research shows us that mussels will absorb as much waste as possible leaving a salmon pens free of most waste. Having a clean pen takes the probability of a virus down, bringing the rate of survival up. Some data suggest that mussels grown very close to the fish farms are capable of ingesting at least 20% of their diet from fish derived sources (Chopin, 2013). A study was done that showed mussels can grow 30% more surface space on their shells making them larger and could consume double intake of the feed waste and feces per day(Chopin,2013). This means the more salmon waste there is, the more the mussels will grow. Mussels not only clean the water of fish waste particles but also grow larger making them easier to sell.
The third is heavier organic solids that also generated from feed waste or feces and that can be consumed by deposit feeders, such as sea urchins and sea cucumbers(Chopin,2013) . The use of extractive deposit feeders, such as sea urchins and sea cucumbers, are effective at reducing deposition beneath salmon aquaculture sites than mussels because they are capable of consuming larger particulates that will typically settle out close to a salmon farm (Chopin, 2013).They get the particles the seaweed and mussels miss. Sea urchins and sea cucumbers were studied and showed that they could grow 30% larger when given more fish waste (Chopin,2013). These two species would thrive in an IMTA system because of their diets.
Oysters are not only known for their taste but also for the way they filter large quantities of water. Each can oyster filter about 50 gallons of water a day (Murray, 2011). Oysters have an important role in the IMTA because they remove nitrogen from the water. Nitrogen can fuel algae blooms that lead to reduced water clarity and low dissolved oxygen. The more they eat the bigger they get and they never stop feeding and filtering (Murray, 2011). Their diet consists mostly of phytoplankton, nitrogen, and carbon. The phytoplankton gives the oysters more meat while the carbon helps their shells grow. The nitrogen helps the oyster develop a thicker shell. Oysters thrive with chemical impurities in the water growing at rapid speeds throughout their lives (Murray, 2011). Oyster filter the nitrogen in the water similar to mussels but oysters need the smallest particles to filter. Oysters filter particles that are between the size of seaweeds dissolved particles and the size of particles mussels consume. Due to an oyster’s diet, they would thrive in an IMTA system by cleaning the fish waste and excess feed thus increasing productivity of an aquaculture farm.
Having these 5 species in the same pen allows them to benefit from each other. The salmon get the food and produce feces while the sea urchins eat the largest particles. Then the mussels filter through particles that are too small for the sea urchins. The oysters filter the smallest of the particles. Then the seaweed takes the dissolved inorganic nutrients and turns them into oxygen. Future IMTA systems must evolve structurally and in terms of complexity to accommodate additional species, and to ensure sufficient water quality and connectivity between trophic levels (Chopin, 2013). The great thing about IMTA is that it can work for many different types of salmon farms like offshore systems or closed containment systems(Chopin, 2013). We think that having an IMTA system with the above species would thrive and produce a higher carrying capacity than a regular monotrophic farm.
In theory an IMTA should work perfectly. The salmon produce excess feed and feces. The sea urchins and sea cucumbers eat the large particles of the wastes. The oysters clean the water and make sure algae blooms do not occur. Mussels pick up the particles that are too big for oysters but too small for sea urchins and sea cucumbers. Finally seaweed and kelp filter the dissolved nutrients and produce more oxygen for a healthier pen. There are many other species that could be added or exchanged for and still have a sustainable working IMTA. This practice was founded in Canada by Cooke Aquaculture along with a man named Thierry Chopin (Greenberg, 2010). Together they ran a successful IMTA system that included salmon, seaweeds, mussels, and sea urchins. That system was a tiny part of Cooke’s business but they are starting to incorporate it in most of their farms (Greenberg, 2010). They made enough money to team up with a few smaller farms to create a company called Heritage Salmon. This new company has salmon, mussels, and seaweed. So far it has been extremely successful but this practice is relatively new and rapidly developing.
The most impractical part of this IMTA farm is getting aquaculture farmers to change to a new system. One way to incentivize farmers to adopt more environmentally friendly practices is to provide tax breaks and grants because the farmer would be providing an ecosystem service along with local food security. There are already many tax breaks for farmers such as getting farm expenses deducted. This means that an expense for a farm that is ordinary for the industry and is accepted in the field of farming can be deducted (IRS, 2015). Another tax break is a repayment of loans. If a farmer takes a loan out on their product they could be deducted for any interest earned over the time it takes them to pay back the loan (IRS, 2015). The final tax break that could help the farmers is through insurance proceeds. This tax break means that insurance will pay a farmer for their crop that is damaged and can not be sold(IRS, 2015). We propose to get a tax break that lets a farmer/business pay less in taxes when transitioning from single species farming to IMTA. We also propose that there will be a tax break on buying the right equipment to transition from their farming style into a IMTA system.
Another benefit to IMTA is better product. The meat of the oysters and mussels would be larger and tastier (Greenberg, 2010). To change a farm into an IMTA system can take a lot of money but if a farmer produces the same amount of original species before and adds the new species in, then they would be getting more of an income. It also gives the farmer a better name because they help the local environment making demand higher and therefore prices increase. Donaher (2012) researched marketing schemes that compared local to nonlocal products in the food industry. He found that a consumer is willing to spend more money on products that are local than nonlocal because it helps the local economy better which inadvertently helps themselves. There are currently little to no local North American Atlantic salmon populations that are not stocked (Greenberg, 2010). They are an endangered species in the wild so putting a label of farmed locally can create a higher selling price. If the farmer says it is sustainable as well as local they can increase seafood prices because consumers are likely to pay more for food that is good for the environment (Donaher, 2012). The consumer is more likely to buy local sustainable seafood because it is believed to be healthier for not only them but also the environment (Donaher, 2012).
IMTA systems can be expensive to start up depending on what type of aquaculture is already being done. Let’s say a salmon farmer wanted to turn his monotrophic farm into a IMTA system. He already has the pen for the salmon and the salmon themselves. All that is needed is the new species and a some equipment. Buying seed, another word for sea creatures in their larval stage, is relatively cheap. Oyster seed per thousand is about $13 but full grown sell for about $2 each. They do not need cages when placed correctly on the ground so no extra equipment is needed. They are low maintenance meaning they only need to placed until ready to harvest so labor costs would be low (Murray, 2011). Mussel seed costs about $.25/lbs but when full grown sell for $5/lbs. They require a floating cage but also do need much labor. Sea urchins and sea cucumbers are hard to find but cost about $4 each and would not be sold. If the farmer wants to start a new farm it wouldn’t be terribly expensive. This is also when our proposed tax breaks would help. As stated earlier in the paper, farmers can use words like local and sustainable to increase the price of the fish. Some people might ask why would I pay more for local than buy the cheaper fish? Most people when buying fish like to spend the money for better fish because cheap fish can lead to illness. Another reason a consumer might pay more is because they want to help local economy(Donaher, 2012).
Integrated multi-trophic aquaculture can mitigate the negative environmental consequences of traditional monoculture such as poor water quality by absorbing nutrients from fish feces and fish feed. Sea urchins, sea cucumbers, oysters, mussels, and seaweed are introduced underneath and surrounding fish pens. These organisms provide an ecosystem service by absorbing the waste that can become harmful. IMTA systems are expensive, nonetheless, our proposed tax breaks will allow farmer to upgrade without risking their livelihood. These tax incentives include interest free loans, and other deductible farm expenses (IRS, 2015). All in all these better practices are feasible on a large scale across many different locations.
Overall, we found that Integrated Multi Trophic Aquaculture is a feasible practice that could potentially help the environment. Through research and data we can conclude that IMTA systems are less harmful for the environment than single species farming. There are ways to make this practice affordable for not only the farmer but also the consumer. Salomon farming might have a negative impact on the environment but there are new ways to create a sustainable system where there is little to no waste.


Anderson, A. (2017). Climate change, tourism and the Great Barrier Reef: what we know. Retrieved from http://theconversation.com/climate-change-tourism-and-the-great-barrier-reef-what-we-know-60108

Berdalet, E., Fleming, L. E., Gowen, R., Davidson, K., Hess, P., Backer, L. C., . . . Enevoldsen, H. (2015, November 20). Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century. Journal of the Marine Biological Association of the United Kingdom. Marine Biological Association of the United Kingdom, 2015, DOI:10.1017/S0025315415001733.

(2003, May 15). Big-Fish Stocks Fall 90 Percent Since 1950. National Geographic. Retrieved April 04, 2017
Chopin, T. (2013). Aquaculture Aquaculture , Integrated Multi-trophic (IMTA) aquaculture integrated multi-trophic (IMTA). Sustainable Food Production, 184-205. doi:10.1007/978-1-4614-5797-8_173

Donaher, E. (2012). Is local produce more expensive? Challenging perceptions of price in local food systems. Local Environment, 1-79. doi:10.1080/13549839.2016.1263940

Gamble, M. (2012, October). All About Aquaculture: Environmental Risks and Benefits. Retrieved from http://www.talkingfish.org/2012/did-you-know/all-about-aquaculture-environmental-risks-and-benefits

Greenberg, P. (2011). Four Fish: the future of the last wild food. 65-74.New York: Penguin Books.

Government of Canada, Fisheries and Oceans Canada, Communications Branch. (2013, June 24). Aquaculture in Canada: Integrated Multi-Trophic Aquaculture (IMTA). Retrieved from http://www.dfo-mpo.gc.ca/aquaculture/sci-res/imta-amti/imta-amti-eng.htm

IRS. (2015, May 19). 10 things to know about farm income and deductions. Retrieved from https://www.irs.gov/uac/newsroom/10-things-to-know-about-farm-income-and-deductions

Kelly, D. (2013, December 8). The difference between seaweed and kelp. Retrieved from http://knowledgenuts.com/2013/12/08/the-difference-between-seaweed-and-kelp/

Matthew, L & Robinson, S & Macdonald, B & Reid, G. (2012) Quantifying the effects of diet and mussel size on the biophysical properties of the blue mussel, mytilus spp., feces egested under simulated imta conditions.” Journal of Shellfish Research 31.(1): 69-77. DOI:10.2983/035.031.0109

Maneveldt, G., & Browne, C. (2015, November 02). 10 facts about seaweeds interesting uses for seaweed. Retrieved from https://africageographic.com/blog/10-facts-about-seaweeds-interesting-uses-for-seaweed/

Murray, E. (2011). Shucked: a life on a New England oyster farm. St. Martians Griffin.

MMO (2013). Social impacts of fisheries, aquaculture, recreation, tourism and marine protected areas (MPAs) in marine plan areas in England. A report produced for the Marine Management Organisation. MMO Project No: 1035. 192. ISBN: 978-1-909452-19-0

Naylor, R. L., Goldburg, R. J., Primavera, J. H., Kautsky, N., Beveridge, M. C., Clay, J., & Troell, M. (2000, June 29). Effect of aquaculture on world fish supplies. DOI: 10.1038/35016500

NOAA Fisheries.(2015, January 14). Atlantic salmon (Salmo salar). Retrieved from http://www.fisheries.noaa.gov/pr/species/fish/atlantic-salmon.html

NOAA Fisheries. (2012, January 12). Feeds for aquaculture. Retrieved from http://www.nmfs.noaa.gov/aquaculture/faqs/faq_feeds.html

Ogden, L. E. (2013, September 01). Aquaculture’s turquoise revolution multitrophic methods bring recycling to the seas. Retrieved from https://academic.oup.com/bioscience/article/63/9/697/260362/Aquaculture-s-Turquoise-RevolutionMultitrophic

Price, C.S., J.A. Morris, Jr. (2013) Marine cage culture and the environment: twenty-first century science informing a sustainable industry. NOAA Technical Memorandum NOS NCCOS.

Sea Cucumber. (n.d.).National Wildlife Federation. Retrieved from https://www.nwf.org/Wildlife/Wildlife-Library/Invertebrates/Sea-Cucumber.aspx

Society, N. G. (2012, October 09). Dead zone. Retrieved from http://www.nationalgeographic.org/encyclopedia/dead-zone/

WWF. Unsustainable fishing. WWF. Retrieved from http://wwf.panda.org/about_our_earth/blue_planet/problems/problems_fishing/


Leave a Reply

Your email address will not be published. Required fields are marked *