Closed Containment and Energy Consumption
Closed containment technologies offer a major step forward in fish farming practices. Providing a physical barrier between wild and farmed fish, closed tanks can eliminate, or greatly reduce many of the negative impacts of out-dated net-cage salmon farming. Having proven to be a technically feasible way to grow salmon, various closed systems are currently being tested to demonstrate viability at a commercial scale.
A criticism leveled against closed tanks is that they require a large amount of energy, making them ecologically unacceptable due to concerns around increased carbon footprint. It is true that closed containment systems require more obvious direct energy than net-cages. But if the root of this criticism is the total ecological acceptability of salmon aquaculture technology, then we must examine more than just energy use to determine the sustainability of salmon farming practices. In doing so, the overall environmental impacts of salmon aquaculture affirm closed containment as the more sustainable technology.
To judge the weight of the energy claim, we must understand:
- why closed containment systems are reputed to require more energy than net-cages;
- the complete picture of environmental impacts associated with salmon aquaculture technologies; and
- how closed containment systems and net-cages stack against each other in terms of overall sustainability.
Putting the Energy Claim into Perspective
The larger energy ‘footprint’ of closed containment systems is due to the need to artificially replicate the services provided to the net-cage industry by the marine environment at no cost to industry. These services include the regulation of water quality and the dispersal of waste into our oceans. Ocean currents and tidal action provide a constant supply of fresh seawater and dissolved oxygen to net-cage farmed salmon, and simultaneously flush waste products from the cages into our marine waters.
But while use of this renewable energy source is portrayed by industry as beneficial from a sustainability perspective, this practice in the open ocean creates a significant environmental footprint. The benthic habitat (ocean bottom) directly below or near net-cage salmon farms is smothered with waste, algal blooms can result from excessive nutrient loads, and disease and sea lice are amplified by the concentration of fish growing in net-cages and can pass through the nets to marine species such as juvenile wild salmon.
So yes, net-cages do use less energy for water circulation and oxygen supply because they tap into naturally occurring services provided by the marine environment at no cost to the industry. But there is a significant cost borne by the marine ecosystem, local communities, and other marine-based businesses such as commercial fishing that rely on healthy, productive oceans.
Environmental Impacts of Salmon Aquaculture and their Potential Solutions:
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Weighing the Environmental Impacts
The intractable environmental issues associated with open net-cage operations such as disease, escapes, pollution, and predator impacts do not have effective solutions, nor are there any on the horizon. These issues are highly complex, involving a number of variables which makes it difficult to identify solutions because you cannot isolate or control for everything. For instance, developed resistance to antibiotics and therapeutant treatments is increasingly common; the round up and removal of escapes is so difficult that a 10% capture rate is considered a success by industry;2 and the act of killing predators does nothing to address the underlying problem.
When it comes to environmental concerns associated with closed containment aquaculture, solutions are already available. Fully closed systems eliminate the possibility of marine mammal deaths resulting from interactions with farmed salmon; escapes and subsequent problems related to invasive alien species; and the transfer of diseases between wild and farmed salmon. Furthermore, depending on the technology used, they eliminate or greatly reduce the need for chemical treatments, solid waste accumulation in the marine environment, algae blooms, and water column pollution.
Further solutions are also on the horizon. For example:
- How energy is generated makes a big difference. Studies have shown that a change from fossil fuels to cleaner forms of energy translates into a fourfold reduction of climate change and acidification impacts.3 All proposed closed containment projects for B.C. intend to use hydroelectricity or geothermal electricity for power, which has the potential to be a cleaner source of power, depending on size and location.
- Improvements to system designs and proposed changes to water treatment can decrease energy demand.4
- Research dollars are being directed to the pursuit of plant-based alternatives to fish meal and oil.
Ultimately, we must consider the overall environmental impact of various aquaculture technologies. No production technology addresses the underlying problem of raising carnivorous fish reliant on feed derived from industrial fisheries for forage fish species such as Peruvian anchovita or North Sea capelin. But if the industry continues rearing salmon, closed containment technology is clearly on a more responsible path for salmon aquaculture.
1 February 2011. – Subhas K. Venayagamoorthy, Hyeyun Ku, Oliver B. Fringer, Alice Chiu, Rosamond L. Naylor and Jeffrey R. Koseff. Numerical modeling of aquaculture dissolved waste transport in a coastal embayment.
2 Backman, Clare, Director of Sustainability for Marine Harvest Canada. “Escaped salmon pose threat to wild stock.” Globe and Mail, 1 July 2008.
3 Aubin et al. 2009
4 D’Orbcastel et al., 2009c
Ayer, N., and P.H. Tyedmers. 2008. Assessing alternative aquaculture technologies: life cycle assessment of salmonid culture systems in Canada. Journal of Cleaner Production 30:1-12.
d’Orbcastel, E.R., J.P. Blancheton, and J. Aubin. 2009. Towards environmentally sustainable aquaculture: Comparision between two trout farming systems using Life Cycle Assessment. Aquacultural Engineering 40: 113-119.
Aubin, J., E. Papatryphon, H.M.G. van der Werf., S. Chatzifotis. 2009. Assessment of the environmental impact of carnivorous finfish production systems using life cycle assessment. Journal of Cleaner Production 17: 354-361.