The Impact of Aquaculture on the Environment

Open ocean aquaculture


The rapidly growing human population is creating an increase in the demand for fish worldwide (Tidwell & Allan, 2001). Unfortunately, the amount of fish captured in fisheries is no longer meeting this demand because the annual production of captured fish has not changed significantly since 2011 (Food and Agriculture Organization [FAO], 2016, p. 4). Overall, 93.4 million tonnes of fish were captured in 2014 but 146 million tonnes of fish were consumed (FAO, 2016, p. 4). Ultimately, overfishing is the main cause of this widening gap between fish consumption and the amount of fish being captured. In 2014, capture fisheries depleted 30 million tons of fish from the most exploited fish species, including Atlantic salmon and trout (FAO, n,d, p. 3). However, aquaculture systems provide a unique solution to alleviate this exploitation caused by overfishing because they are designed to breed and harvest fish rather than capture wild species (National Oceanic and Atmospheric Administration [NOAA], n.d. a). Aquaculture is becoming a more popular fish production method as it has an annual increase of 6 percent and is projected to produce over half of the fish consumed by 2025 (FAO, 2016, pp. 22, 172). In contrast, capture fisheries’ production rates are steadily declining and are predicted to collapse by 2048 (National Geographic, 2016, para. 8). In addition to providing relief for exploited fish populations, the success of aquaculture systems is attributed to the ability to selectively breed and rear fish that have a higher growth rate (Hindar, Fleming, McGinnity & Diserud, 2006). This increased growth rate can increase fish production and ultimately reduce fish price by almost 2 percent by the year 2030 (World Bank, 2013. p. xviii). Valderrama, Hishamunda & Zhou (2010) also demonstrate that the global aquaculture industry provides 16 million jobs worldwide (p. 24). Overall, increasing aquaculture production, can prevent large amounts of malnutrition in the human population by providing an inexpensive protein source (FAO, 2016).

Since aquaculture will become the dominant production system for the global fish supply, many management practices in the aquaculture industry must be addressed and refined in the coming years to assure viability of aquaculture systems. Aquaculture comes in multiple versions, two of which are open systems versus closed systems; this paper is focused on open systems, which are usually found offshore in coastal areas, exposed to natural environments (Lawson, 1995).  These systems are high-risk because they allow unchecked interactions between the farmed fish and the surrounding environment, which leads to free exchange of disease, parasites, and fecal matter (Aquaculture Methods, 2016). The only barrier between the harvested fish and the wild population is a rigid cage or netting system. Often times, the netting will vary by size and type of attachment to the seafloor (Texas A&M, n.d). When these netting systems are damaged during inclement weather such as snowstorms or hurricanes, it allows fish to escape from the open systems (Center for Food Safety, 2012). There were 25 million reported fish escapes worldwide and the majority occurred when netting was damaged during severe weather conditions (Center for Food Safety, 2012, p. 1). Aquaculture is only going to continue to grow at a rapid pace because there is increasing pressure to alleviate the stress on heavily consumed populations of fish.  However, if large amounts of fish continue to escape they could pose a threat to native species by increasing competition and altering the natural gene pool.

Despite the growth and production in aquaculture, protecting the stability of native fish populations is a major concern for fisheries who still practice catching wild fish in open waters. One of the threats posed by escaping fish is how they can alter the food chain of ecosystems by competing with wild fish for mates, space, and prey (Naylor et al., 2005). Native species can suffer a decrease in population size, which is largely due to their displacement by the escaped fish invading their habitat (Kohler & Courtenay, 1986).  Also, the alteration of food chain in ecosystems can impact the economy/livelihood for the people who live in areas adjacent or near an outbreak, depending on the severity and implications of such an outbreak.

Introducing a non-native species can alter the habitat/communities of native species; the impact is greater if the non-native species is considered an invasive species (Deegan & Buchsbaum, 2005). The invasive carnivorous cobia fish can reach a maximum of 176 pounds at an astonishing two meters in length; their large, muscled body covered by a thick dark brown skin along their back is an unusual sight in the East Pacific Ocean (King, 2016 para 1). A year and a half ago thousands of these predatory fish escaped the enclosures of an aquaculture system off the coast of Ecuador (Kwok, 2016, para 2). At a rate of 200 miles per month, these fish have steadily moved up the west coast of Central America and were spotted near Panama several months after their escape (Cohen, 2016 para. 2). In February of 2016, researchers projected that there is a 50 percent chance the non-native fish population will reach the California coast and invade native Pacific salmon habitats (Cohen, 2016, para. 3). To compare, the cobia can reach a mature weight at 11 months, growing three times as rapidly as the native Pacific salmon, which require 3 years to reach a mature weight of, at most, 100 pounds (Cohen, 2016, para. 6).  As the research biologists Milton Love describes, when the cobia population arrives in the salmon’s natural habitat, it has the potential to bring predation and competition with it (Cohen 2016).

Similar to the cobia,  an invasive species that outcompetes native species is the zebra mussel in the Great Lakes (Heimbuch, 2009). In contrast to the cobia, when zebra mussels escape they affect the food chain from the bottom up because they are known to consume great quantities of plankton versus larger marine animals.  Plankton make up the vast majority of bases of marine food chains, which gives them a very important role in the ecosystem; plankton shortages can cause a cascading effect in an ecosystem by limited the availability of food, which increases competition for resources and alters the food chain as the weaker species are eliminated (Strayer, Hattala & Kahnle, 2004; The Editors of Encyclopedia Britannica, 2013).  Thus, these zebra mussels are in direct competition with fish that also consume plankton in the ecosystem (Kohler & Courtenay, 1986).

Fish that escape from various open aquaculture systems also have the ability to alter the gene pool of the native species in the environment.  The gene pool is the stock of all genes, or genetic information (which encode for things such as amount of muscle, size of fish, etc.), in an interbreeding population of a specific species (“The gene pool”, n.d.).  When the gene pool is large, that’s indicative of genetic diversity, which means the population has a high survival rate, or is very robust.  Therefore, if there are very few males to breed with a lot of females, the gene pool will decrease, and the population won’t be as strong (“The gene pool”, n.d.).  This is similar to inbreeding in mammals, where the more closely related the breeding couples are, the more health problems the offspring will have (Ochap, 2004).  When fish escape from these aquaculture systems, they breed with the native populations of fish that lead to an introduction of new genes into the gene pool that take over, causing the gene pool to decrease in size, which potentially leads to a decrease in the survival of the offspring in the environment (NOAA, n.d. b). When native and non-native species breed, it weakens the genetic purity and fitness of wild populations, which decreases their chances for survival (Black, 2001, p. 90).  In the Gulf of Maine, the native Atlantic salmon is in danger of going extinct because they exhibit poor fitness and poor breeding abilities (poor spawning stock); therefore, if any interbreeding  occurs with another species, the native species may go extinct quicker than expected (NOAA, n.d. b).  In Norway, farmed Atlantic salmon also frequently escaped from fish farms and hybridized with the native Atlantic salmon (Simms, McDowell & Graham, 2016).  Similarly to salmon in the Gulf of Maine, these new genes from the farmed salmon invaded the gene pool and caused the offspring of these interbreedings to have lower survival rates and lower fitness (Simms et al., 2016).

Across the Atlantic, in the Northern Rocky Mountains of the United States, hybridization between invasive rainbow trout and the native cutthroat trout is occurring; the effects of this interspecies hybridization are nearly identical to the intraspecies (same species) hybridization occurring in Norway’s salmon.  The cutthroat trout naturally live in streams that are less than 11 °C (51.8 °F), these are “cold” streams; the rainbow trout naturally live in streams that are above 11 °C, or “warm” streams (Muhlfeld et al., 2017, p. 1).  There are extensive stocking records that document the constant input of rainbow trout into streams around the Rocky Mountains.  In order to survive the rainbow trout, the cutthroat trout survived exclusively in cold streams where the rainbow trout couldn’t survive (Joyce, 2017).  However, as climate change becomes a bigger issue, the high-altitude streams are becoming warmer, which enables the rainbow trout to now live where the cutthroat live.  The hybridization of these two species leads to jumbling of these vital survival genes in the cutthroat, which results in hybrid offspring that are “feeble [and] less fit” in biological terms (Joyce, 2017, para. 7).  Even though the practice of stocking these streams ended over 40 years ago, hybridization increased over time at over 50% of the sites sampled, which equates to 291 sites (Muhlfeld et al., 2017, p.1).  This is a big concern because over 74% of the sites (430 sites) were not initially hybridized; this means that over 40 years, even with knowledge of the problem and efforts being made to prevent the rainbow trout from becoming invasive, the gene pool continued to deteriorate at a drastic rate (p. 1).  In addition, over 58% of the hybridization sites (168 sites) were located in cold streams, demonstrating the fact that the rainbow trout are invasive and have successfully altered the gene pool (Muhlfeld et al., 2017, p. 1).

This relates to fish escaping because, in both scenarios, humans are introducing an invasive species into the environment and these species are altering the gene pool in a negative manner.  One difference between the two scenarios is that, with the rainbow trout, people introduced the fish directly into the system with no restraint and no regard for the natural wildlife; with the salmon of Norway, the fish are escaping from open aquaculture systems by bypassing the restraint mechanisms put in place by the fish farmers (Karlsson, Diserud, Fiske & Hindar, 2016; Muhlfeld et al., 2017).  Another significant difference between these scenarios is that, once it became evident that the restocking of rainbow trout in the ecosystem harmed the native wildlife, it was stopped altogether.  However, when it became evident that fish escaping was harming the environment, improvements to netting weren’t implemented immediately; they still haven’t applied enough improvements throughout the world’s aquaculture systems to alleviate the problem, which continues to persist.

Projections demonstrate the dominant supplier of fish around the world will be aquaculture, and with this power comes the responsibility of implementing new regulations and innovations to reduce the amount of escaped fish from open aquaculture systems. Norway recently engaged in research to find long lasting innovations to decrease the interference of escaped fish in the gene pool (Aarvig, 2013). In 77 out of the 147 rivers sampled in Norway, hybridization from escaped salmon and wild salmon was found; these numbers indicate that over 52 percent of the rivers contained gene pools that were altered by these escaped fish (Bajak et al., 2016, para. 2).  In addition, the genetic material found in farmed salmon was present in almost 50 percent of the wild populations tested (Karlsson et al., 2016). To remedy this, scientists in Norway are promoting a genetic innovation that sexually sterilizes farmed fish to restrict gene flow (Simms et al., 2016).  Scientists from six fish farming companies successfully produced one million sterile fish in 2013 by applying pressure to salmon eggs. (Aarvig, 2013, para.1). When pressure is applied to the eggs the embryo will divide to have triploid chromosome (XXY) (Aarvig, 2013). So far, this method is successful with rainbow trout and six norwegian fish farming companies already adopted these methods. However researchers still do not understand how these genetic modification affect the nutritional needs of the fish. Once a proper nutrition plan is put in place, genetic sterilization is a viable solution to mitigate damage to the ecosystem if/when fish escape from these open systems (Aarvig, 2013).

In Norway the Norwegian Technical Standard  (NS 9415) was implemented in 2004  (Jensen, Dempster, Thorstad, Uglem & Fredheim, 2010). Under this legislation new nets installed undergo a technical assessment and a certification process (Norwegian Ministry of Fisheries and Coastal Affairs, 2014).  Fish farms that are accredited can analyze netting by assessing whether or not the netting has the ability “to cope with environmental forces (e.g. wind, waves, currents) at fish farm sites” (Jensen et al., 2010, p. 79). The results of the analysis prompted several farms in Norway to voluntarily replace their current netting with stronger, weather resistant material (Jensen et al., 2010). As a result, the amount of escaped fish from salmon aquaculture systems was reduced from greater than 600,000 fish escaping annually to less than 200,000 (Jensen et al., 2010, p. 71).

Overall Norway has made significant progress in this field on a national level by performing genetic modification research and implementing NS 9415 of 2004 (Jensen et. al, 2010). Both implementations address competition and alterations to the gene pool that have occurred from escaped fish in Norway (Jensen et. al, 2010). Legislators in other nations with substantial aquaculture should adopt both the accreditation/certification program and fund research for genetic modifications to impose a global prevention of escaped fish. However lawmakers must adapt the Norwegian system to accommodate for economic differences. Some countries might benefit if they provide incentive to farmers to improve their netting. Developed countries such as the United States have a similar system that provide farmers with 300 billion dollars in agriculture subsidies (Borders & Burnett, n.d). Farmers would more readily improve their netting systems, if they were provided the funding to do so.

Even though escapes from open-system aquaculture systems can potentially increase the risk of economic losses for commercial fisheries and conservationists, legislators and global funding programs should invest funds in the prevention of escaped fish as Norway did (Naylor et al., 2005). Declines in wild fish populations caused by fish escapes are more likely to affect commercial fisheries and conservationists than aquaculture industry. Open-system aquaculture is considered as a means to reduce pressure on wild fish populations, yet the capture of wild salmon is greater today than it was prior to 1990 (Naylor et al., 2005, p. 432). If production of reared salmon is increased to supplement the decline in wild populations, the costs to the commercial fishing industry could potentially increase with higher licensing fees. Costs to taxpayers could also increase due to hatchery subsidization. The aquaculture industry itself suffers economic loss, but in a different way.  The most direct cost to the industry is forgone revenue, the money lost that was invested in stock. The costs in some cases are balanced by insurance payments for damage caused by storm events. The effects on wild fish populations do not pose a financial threat to the aquaculture industry (Naylor et al., 2005). The fact that the aquaculture industry doesn’t suffer financially due to escaped fish is the reason why policy and enforcement is so imperative.  Even when there is chronic leakage (escapes), aquaculture companies often weigh the benefits of reducing/eliminating escapes versus the costs of improving the structural strength/durability of their equipment (Naylor et al., 2005).

Conservation values are a bit more abstract, but there are methods that are used to measure the costs. Loomis (1996) describes two forms of analyses that exist, which are willingness to pay (WTP) and willingness to accept (WTA).  WTP is what amount people are willing to pay to protect a specific species or ecosystem, and WTA is their willingness to accept an amount of damage to a species or ecosystem. Washington State conducted a survey showing that the residents’ WTP was $50-$70 per household for wild salmon conservation (Loomis, 1996, p. 445). The WTA is potentially infinite because open system escapes may contribute to the extinction of certain wild salmon population, increasing the demand for farm grown salmon (Naylor et al., 2005). Research performed by Jackson (2015) shows that a total of 252 escape events of various magnitudes in 6 European countries resulted in a product loss of $50 million (Jackson et. al, 2015, p. 24-25). In addition to the losses in Europe, the zebra mussels in North America cost the Great Lakes’ utilities $267 million from 1989 to 2004 because they practically clogged pipes used for drinking water (Connelly, O’Neill, Knuth & Brown, 2007, p. 1). These assessments highlight the importance of why sufficient funding should be provided to assist in the prevention of escapes.

Farmers need to implement significant improvements to aquaculture to reduce the threat that escaped fish have on native species. This is achievable through global cooperation to provide large aquaculture production systems with improved equipment and adequate funding.  Aquaculture is growing at a rapid pace in order to keep up with the growing demand for fish and in order to prevent fish escaping from becoming exacerbated, necessary measures must be taken by fish farmers and legislators.  If preventative measures are not implemented soon, it’s possible that the problem can become “uncontrollable” in some areas, leading to a bigger conundrum that cannot be dealt with easily (Kwok, 2016).  Aquaculture is on the path to becoming the lead producer for human fish consumption globally as long as the production loss and environmental impacts of escaped fish are reduced and proper preventative measures are put in place to ensure fish escapes are minimized or, better yet, completely eliminated.


Kevin Keough – Natural Resource Conservation

Miranda Senft – Pre-Veterinary

Emma Vaughan – Pre-Veterinary

SarahBeth Welch – Sustainable Horticulture


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One Comment

  1. I never knew this:
    “open-system aquaculture systems can potentially increase the risk of economic losses for commercial fisheries and conservationists”
    – DD,

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