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Fish farm

Still waters at an IMTA fish farm hide a wealth of ecological activity

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    Kelp grows near mussels and salmon in an IMTA farm

Can salmon farming be sustainable?

Emma Bocking

20th October, 2009

Salmon farming is renowned for its local environmental pollution, but now some fish farmers are starting to look at fish waste as an untapped resource

Aquaculture just seems to be one of those words that really riles up environmentalists, and with good reason - the effects of pollution from fish farms are well documented.

But fish farming is not going away. In fact, it is the fastest growing food production industry in the world, and accounts for almost half of our seafood consumption. Finding a way of making aquaculture more sustainable is a future priority for those in the industry and those making the rules.

With the longest marine coastline in the world, it is perhaps not surprising that Canada is behind only Norway and Chile in the production of farmed salmon. And it is on this coastline that some pioneering aquaculturists are using ecological approaches to reduce the impact of their business.

Integrated Multi-trophic Aquaculture (IMTA)

IMTA is a simple idea built on a complicated series of details. Basically, its goal is to recreate a balanced ecosystem within a fish farm.

Part of the problem with fish farming is that a large number of fish in a cage produce a large amount of waste, which floats through the bottom of the enclosure down to the seabed, where it can become a pollution problem.

In an IMTA system, by-products of the fed species (excrement and uneaten food) are recycled to become inputs for at least two other species. Shellfish are grown to take in particulate organic matter, and seaweed species will use inorganic wastes, such as nitrogen.

Researchers are also experimenting with a fourth component to absorb larger organic matter, using various species of sea urchins or sea cucumbers. Shawn Robinson, a scientist with the Department of Fisheries and Oceans Canada and a lead researcher in IMTA development on the East coast, explained why this system makes sense. Fish, he says, like humans and all other organisms, are inefficient at converting and storing food as energy.

'Think of all the food we buy at the grocery store every week; we can't possibly store all of that, imagine how big we would be! That's why we're going towards this IMTA, to catch that extra energy potential,' says Robinson. Excess 'energy' originally intended for the fish is taken up and used by species further down the food chain.

A diagram of an IMTA system
A diagram of an IMTA system, showing the interlinked ecosystems under the water. The bright green areas on the left-hand side are kelp; the wavy blue lines are mussels; the pink triangles are shellfish; the main cages contain salmon, and the bottom purple 'strip' contains sea cucumbers, which feed on more solid waste
The bottom line

So far, Robinson and his colleague, Thierry Chopin, a professor at the University of New Brunswick, have concentrated their IMTA efforts in the Bay of Fundy in the province of New Brunswick. The Bay is home to ninety-six fish farms (mostly Atlantic salmon, although some grow cod), and it has taken eight years for Robinson, Chopin and their team to convert just six into IMTA farms, with ten more in transition.

At the moment the IMTA concept is still in its infancy, but Chopin explains that from an industry standpoint, IMTA makes economic sense. An economist on the research team has determined that over a ten year period encompassing five cycles of salmon, a farmer will make more money with IMTA than with a conventional monoculture model.
'When you show these numbers to industry, they say "huh, interesting",' says Chopin.

All of the components of an IMTA system are chosen for commercial value, as well as being native or indigenous to the Bay of Fundy region: mussels and kelp are the most common. Last year, the first crop of IMTA blue mussels was sold to markets in Maine, Quebec and California, with positive feedback.

It's not just the industry that is intrigued: NGOs have started arriving to take a look at the systems. The Soil Association was one of the first to contact Robinson and Chopin for more information, and Greenpeace International and WWF endorse IMTA as a sustainable solution for aquaculture. Even David Suzuki, renowned for his sceptical views on farmed salmon, visited the IMTA sites earlier in the year with his daughter, and was reportedly optimistic.

The researchers are even more excited. Enthralled by the possibility of a new peace between greens and fish farmers, Chopin describes IMTA as 'the convergence that allows the dialogue [between industry and environmentalists] to take place.'

Nutrient Credits?

In an effort to make the economics of the approach even more favourable, some are now looking to market the 'services' provided by the different trophic layers in the IMTA system.

In coastal environments, high concentrations of nutrients such as nitrogen and phosphorus are a key issue, leading to the much-discussed marine 'dead zones' created when algal blooms die back.

To address this, Chopin backs the concept of a nutrient credits system. Seaweeds and mussels sequester excess nutrients in the water, and when harvested remove these from the marine ecosystem. Why not credit IMTA farmers for capturing those nutrients, Chopin asks.

Like all 'offset' and trading systems, it will have its supporters and its critics, but Chopin believes that its role in making IMTA more attractive should not be ignored.

Beyond IMTA

Stephen Cross, president and CEO of the Pacific SEA-Lab Research Society in British Columbia, pictures his IMTA-type system as built on three pillars: nutrient absorption and sequestration by shellfish and seaweeds, reduction of the farm's carbon footprint through the use of electric motorboats and on-site generated wind power, and best or organic management - antibiotics have not been used. Cross' project - 'SEA' stands for Sustainable Ecological Aquaculture - has met with approval from both NGOs as well as First Nations communities, which are interested in implementing his techniques on farms in their territories.

Like his counterparts on the East coast of Canada, Cross is confident in his model for sustainable aquaculture.
'If you can be more environmentally friendly and make a buck at the same time, it's the best of both worlds,' he says.

Emma Bocking is a freelance journalist

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