TO EAT OR NOT TO EAT: FARMED FISH
As a nation we are consumed by the food we eat. We worry about our next meal as soon as we start to feel those tell-tale pangs of hunger, and often before that. Food rules our lives. We watch hours of television programs about food, plan most of our social lives around it, use it to celebrate when we’re happy, and use it to make us happy when we’re sad (comfort food anyone?). Large parts of most of our days are spent buying food, preparing food, waiting for food, and eating it. We stress over the vitamin, protein, and caloric content of what we eat (as an image obsessed society. However, we don’t all think about exactly where our food came from, how exactly it was grown/made/processed, and what effects it may have on anything but us. We are slowly improving in this respect, becoming more conscientious about these things. Organic and local foods are getting more and more popular, for example. We are often told to not eat certain foods but often we aren’t told why. Fore example, we are often told that we shouldn’t eat farmed fish. The main concern with farmed fish is the detrimental effect that the farms have on the environment. What are these effects? Why are they so significant?
Salmon is a highly nutritious food and its popularity is increasing quite quickly, especially in BC. Salmon is farmed off the coast of British Columbia in open net cage pens designed to mass produce the fish to supply our demands (30 m by 30 m each holding 50,000 fish). Most of the environmental problems associated with salmon farming in BC waters result from the fact that waste from the farm can fall into the surrounding water and to the ocean floor through the netting of the pens [8].
As one can imagine, 50,000 fish produce massive amounts of organic waste, however, one farm does not consist of only 50,000 fish, and on average a farm will contain 700,000 fish [8]. The total organic waste produced in BC (85 open net farms) is equivalent to the amount of sewage produced by a city of 500,000 people [7]. Food wastes and fish feces are the major contributors to this waste but dead fish and blood (if the fish are harvested and bled at the farm) also contribute. This waste then piles up on the ocean floor as sediment beneath the farms and to a certain extent in the water column between the farm and the ocean floor. The first concern with the large sediment build up is the increase in decay that will take place to an extent much larger than is normal for other areas of the ocean. The decaying process requires large amounts of oxygen, depleting the dissolved oxygen in the water surrounding the farm, and produces toxic gases such as ammonia, methane, and hydrogen sulphide. The second problem is the build up of nutrients, especially nitrogen, phosphorus, and carbon, all of which are present at high concentrations in organic waste, in the sediment [6, 10]. These nutrients will become “locked” in the sediment because the sediment builds up much faster than they can be removed from the waste to be recycled [10]. The excess nitrogen present may also help promote algae blooms. These algae blooms will further decrease the dissolved oxygen in the surrounding water when they die and decay [6, 10]. These factors alone have a large impact on the environment by directly affecting the sea life below the farms. A drastic reduction in the diversity of the sea life in the vicinity of the farm is seen, even to the extent sometimes there is a complete lack of life directly below the farm [10].
Not only are organic pollutants released from the farms, chemical pollutants – such as antibiotics, antifouling paints, feed additives, and pesticides – are also released into the environment causing many problems [6]. Antibiotics are problematic because the way they are administered, by addition to the food, results in a loss into the environment in two ways. The first way occurs because the antibiotic is poorly absorbed by salmon’s intestines, which is the case with the commonly used antibiotic Oxytetracycline, and is then present in high levels in the feces. The second way antibiotics are released into the environment is by food waste and accumulation in the sediment. The microbes in the sediment, those that are important for breaking down the sediment and for nutrient recycling, are usually killed by antibiotics. Also, when bacteria are exposed to antibiotics for long periods of time they can mutate and develop resistance to the antibiotics. This will not only occur in the useful bacteria but in any bacteria present, which may lead to resistant strains of disease causing bacteria. These bacteria will then be present under the farms and in the salmon themselves, wild and farmed [2]. It is unknown whether or not any of the other food additives, such as colouring agents and preservatives, have any environmental effects [6].
Another type of chemical pollutant is a result of the use of antifouling paints on the nets and the boats of farms to decrease the amount of cleaning required (preventing build up of plant and animal growth on the nets and boats). These paints contain a high level of copper which can leach into the surrounding water. It was found in by the one year Interim Monitoring Program done by the BC government 2001 that 48% of the farms in BC had copper and zinc (added to the food to prevent cataracts in the fish) levels above what is deemed as “safe”. However, the “safe” levels of copper and zinc are actually above the actual safe level of most marine organisms and when together, copper and zinc are even more toxic. These chemicals will have a detrimental affect on the marine animals in the vicinity of the farm by affecting their chemoreceptors and nervous systems. This will in turn have a negative affect on the sea life diversity [6].
Pesticides are a third type of chemical used in salmon farms that can pollute the surrounding environment. They are used to kill sea lice, a parasite that thrives in the farm environment. The most common pesticide used is ivermectin. This pesticide works by disrupting neurological processes and binding to cell membranes and increasing their permeability to chlorine ions (an ion that is present in ocean water in high concentrations) [2]. The fish are treated with the pesticides by being added to their food or by immersing the fish in a bath of pesticides for a short period and then releasing the pesticides and fish into the water [6]. The pesticides may then exert similar effects on some of the marine animal life that they had on the pests [2].
Sea lice are not only an issue for the farmed salmon, they also are a major problem for wild salmon. The lice can be passed from the farmed salmon to the wild salmon, something that may not actually be a huge problem for the adult salmon because sea lice are benign on adults. However, sea lice are rare on juvenile salmon and are lethal to them. Normally, juvenile salmon enter the ocean months before the adult salmon come back. This means that there is a period of time when the juvenile fish do not come into contact with adults and so are not exposed to sea lice until they are adults. The farms create a unique situation where this period of time when the juveniles and adults do not come into contact is removed. The juveniles come into contact with farmed adult salmon infested with sea lice on their way out into the ocean. Because sea lice are lethal to juvenile salmon if more than 2 are present on one fish at a time, sea lice increase the mortality rate of juvenile salmon and will have a negative effect on the populations of wild salmon [5].
Pollutants released from salmon farms are not the only environmentally detrimental effect of the farms. One major problem, and possible the greatest threat to the marine ecosystem off the coast of BC, is the accidental release of Atlantic salmon into BC waters. Atlantic salmon are the main salmon used for farming because they are much easier to farm than Pacific species. However, it has been estimated that over one million Atlantic salmon have been accidentally released into BC waters [1, 7]. When farming of Atlantic salmon started it was believed that they wouldn’t be able to survive and reproduce if they escaped, however, they have managed to do both. Atlantic salmon have been caught in fishing nets and even reported to have moved as far as Alaska [1]. What is even more shocking is that they have been shown to be reproducing in BC rivers. Juveniles that were found in BC rivers were analyzed to determine if they were from natural spawning or from the farms. It was determined through scale and guy analysis that they were from natural spawning. This is of great concern because they could possible end up competing with Pacific species, which are already fragile, for resources and space [9].
Salmon farming is only one example of why we need to pay more attention to where our food comes from. It is important if we want to invest in future generations. If our beautiful BC coast is over farmed we could destroy or at least dramatically change it leaving nothing for future generations to enjoy. A similar situation could happen with other food choices we make. We need to become responsible citizens and take care of the world and people around us, especially as technologies advance. We, as consumers, have a massive amount of power over what is done to our food which is a huge responsibility. We cannot take that responsibility lightly. So next time you buy salmon, pay attention to where it came from and then apply this to other foods that you eat as well.
References Cited
1. Dey, P. (October 17, 2001). Tracking an alien species. Retrieved October 9, 2006, from University of Alberta, ExpressNews Website
2. Drugs used in the salmon farming industry. (n.d.). Retrieved October 9, 2006
3. Hites, R.A., Foran, J.A., Carpenter, D.O., Hamilton, M.C., Knuth, B.A., and Schwager,
S.J. (2004). Global assessment of organic contaminants in farmed Salmon. Science, 303, 226-229.
4. Hites, R.A., Foran, J.A., Schwager, S.J., Knuth, B.A., Hamilton, M.C., and Carpenter,
D.O. (2004). Global Assessment of polybrominated diphenyl ethers in farmed and wild Salmon. Environ. Sci. Technol., 38, 4945-4949.
5. Krkošek, M., Lewis, M.A., Morton, A., Frazer, L.N., and Volpe, J.P. (2006).
Epizootics of wild fish induced by farm fish. PNAS, 103, 15506-15510.
6. Open Net Cage Fish Farm Pollution. (n.d.). Retrieved October 9, 2006.
7. Salmon Farming: Environmental impacts of farming salmon. (n.d.). Retrieved October 9, 2006.
8. Salmon Farming: What is Salmon Farming? (n.d.). Retrieved October 9, 2006
9. Volpe, J.E., Taylor, E.B., Rimmer, D.W., and Glickman, B.W. (2000). Evidence of
natural reproduction of aquaculture-escaped atlantic salmon in a coastal British Columbia river. Conservation Bioloy, 14(3), 899-903.
10. Wu, R.S.S. (1995). The environmental impact of marine fish culture: Towards a
sustainable future. Marine Pollution Bulletin, 31(4-12), 159-166.
