If you’ve read my most recent article concerning the disaster of overfishing, then you are well aware of the crisis that we face regarding the sustenance of global fish stocks. For those of you who haven’t, basically, global fish stocks such as the Bluefin Tuna, Thunnus thynnus, along with countless other species, are declining precipitously as a result of exhaustive human exploitation. As such, many of you may have pondered the idea of aquaculture – shouldn’t fish farming eliminate any chance of a fish species becoming extinct? Simply put, the answer is no. In principle, aquaculture can indeed increase fish stocks of particular species and keep fish on the market. So, to an extent, aquaculture can be economically useful. However, the downfalls of aquaculture on both an ecological and economic level far outweigh the benefits of this practice.
As a marine ecologist conducting research on the Bay of Fundy, I am no stranger to the sights of aquaculture. Here in southwestern New Brunswick and all around the world, salmon farming is extremely popular. Since the 1970s, salmon farming has exploded, currently producing more than 1 million tonnes of salmon worldwide each year (ICES, 2006). In contrast, it has been suggested that aquaculture as a whole produces upwards of 52 million tonnes of fish annually, with a financial yield of approximately $78.8 billion dollars US (Phillips, 2009). At a glance, aquaculture sounds great! Huge increases in the number of particular fish species and plenty of food and income. This is exactly what the industry wants you, the general public, to believe. They, however, neglect to provide the negative ecological impacts that accompany aquaculture; effects that are devastating to ecosystems and a wide array of organisms that are associated with fish farming.
There are numerous consequences to aquaculture including contamination, feeding methods, genetic modification, and the possibility of escape, which entails a whole other suite of problems including disease, parasites, and increased predation on established natural fish populations (Hites et al., 2004; Mcleod et al., 2006; Ford & Myers, 2008; Phillips, 2009).
Because of the material composition of the cages, many fish farms accrue high levels of heavy metals and toxins. For example, Hites et al. (2004) found high levels of organochlorine contaminants in salmon farms in Scotland, Norway, and eastern North America. They suggested that farmed fish from these areas should be consumed by humans no more than 3 – 6 times annually to avoid poisoning.
Additionally, most fish species that are bred in captivity are carnivores. For example, the Atlantic salmon (Salmo salar) is a carnivorous fish, meaning that it will only consume other fish and invertebrates. As such, when bred in captivity, the salmon are often fed ground-up fish or shrimp. Consequently, in order to sustain the 1 million tonnes of salmon that are produced annually via salmon aquaculture, many smaller species of fish and marine invertebrates are overfished. Although some farms have tried using fish and pig feed which is altered to taste like fish, this decreases the nutritional value of the salmon, particularly in Omega 3, and is rarely used in place of fish feed (Kadir-Alsagoff, 1990). This is purely inefficient and absurd; if we overfish the species that feed the farmed fish, we would not only be depleting natural fish stocks, but eventually we would deplete the farmed stocks as well, with no way to recover them.
It would be more ecologically and economically plausible to consume the small fish and invertebrates directly. Moreover, farmed salmon are often genetically modified to grow faster and bigger (McLeod et al., 2006). Subsequently, more food is needed to sustain the larger salmon, depleting the natural stocks of smaller fish and shrimp even faster. Ultimately, the behaviour of the farmed salmon will be modified to some extent. For example, genetically modified fish may spend more feeding as they will need to consume more food in order to compensate for the increased amount of energy expended in this rapid and increased growth – it only makes sense. With the frequent escape of raised fish into the wild resulting from damage to the cages (Phillips, 2009), this increased need to eat can lead to increased predation pressure on natural fish populations. Moreover, farmed fish are typically accompanied by parasites which can easily spread to wild populations of fish. For example, in the 1970s, the monogenean parasite, Gyrodactylus, spread from salmon farms in Norway, resulting in devastation to natural salmon populations (Stead & Laird, 2002). Moreover, sea lice accompany almost all fish farms and can result in significant declines in salmonoid abundance (Ford & Myers, 2008; Phillips, 2009).
In general, the presence of salmon farms and other artificially raised species has devastating impacts on local populations of fish and other organisms. Ford & Myers (2008) found that survival and abundance rates of numerous fish species significantly decreased with increases in salmon farming, some of these decreases amounting to more than 50%. This is not only evident in salmon aquaculture, but in many of artificially raised species. With the exhaustive amount of fish produced annually by aquaculture (52 million tonnes), you can begin to see the ecological impact that this industry can have on natural fish populations. As Dr. Boris Worm points out, we cannot replace natural fish populations. So the next time someone tries to tell you that the crisis of overfishing can be simply resolved through aquaculture, kindly tell them to “try again”.
Ford, J.S. and Myers, R.A. (2008). A Global Assessment of Salmon Aquaculture Impacts on Wild Salmonids. PLoS Biology 6: 411-417.
Hites, R.A., Foran, J.A., Carpenter, D.O., Hamilton, C., Knuth, B.A., and Schwager, S.J. (2004). Global assessment of organic contaminants in farmed salmon. Science 303: 226–229.
International Council for the Exploration of the Sea. (2006). Report of the working group on North Atlantic salmon. (WGNAS) 13 April 2006. ICES Headquarters. ICES CM 2006/ACFM: 23.
Kadir-Alsagoff, S.A., Clonts, H.A., Jolly, C.M. (1990). An integrated poultry, multi-species aquaculture for Malaysian rice farmers: A mixed integer programming approach. Agricultural Systems 32: 207-231.
Mcleod, C., Grice, J., Campbell, H., and Herleth,T. (2006). Super salmon: The industrialisation of fish farming and the drive towards GM technologies in salmon production. CSaFe, Discussion paper 5: University of Otago.
Phillips, S. (2009). Marine aquaculture: Environmental impacts: Sea lice and escapement and federal actions. Pacific States Marine Fisheries Commission. Available online from http://aquaticnuisance .org
Stead, S.M. and Laird, L. (eds.). (2002). Handbook of salmon fishing. Chichester: Praxis Publishing Ltd.