Recycling like Mother Nature: The Integrated Multi-Trophic Aquaculture Project

Salmon aquaculture is a serious business in Atlantic Canada. It employs thousands of workers and is the economic backbone of many coastal communities. As with any business, aquaculture entrepreneurs are always looking for improvements that will bolster their bottom line and give them an edge in a highly competitive market. At the moment, one of the most promising concepts for a new way of doing business is coming from a consortium of research scientists, economists, government regulators and industry representatives who are applying lessons learned from Mother Nature, with great success, to aquaculture in the Bay of Fundy.

The Integrated Multi-Trophic Aquaculture (IMTA) project started five years ago on the premise that mass farming of a single species of fish is an inherently wasteful process. Typically, it takes three to four times as much food to get a tonne of salmon, the same as with all other organisms, including ourselves. Much of this carbon- or nitrogen-rich waste ends up on the bottom of the sea cage or dissolved in the water, sometimes creating environmental concerns. In nature, there is always a species that finds a feeding niche in another species’ waste. So why not build a customized ecosystem that would take up the slack in the salmon farm? And better yet, why not build it with species that have an economic value of their own?

According to Shawn Robinson, a scientist with Fisheries and Oceans Canada (DFO) and an IMTA co-leader, the project was triggered by a salmon farmer who came to Robinson’s office at DFO’s Biological Station in St. Andrews, New Brunswick, to ask some questions about diversifying his operations in the Bay of Fundy by adding mussels to the mix. The idea was intriguing to Robinson and to his colleague and IMTA co-leader, Thierry Chopin, a professor at the University of New Brunswick. It quickly grew into a full-fledged research project, with solid funding, that is opening up exciting, economically advantageous opportunities for Canada’s aquaculture industry.

Harvesting a crop of IMTA kelp for the sea vegetable market from longlines of seaweed grown near an IMTA salmon aquaculture site in the Bay of Fundy.

The model they set out to test combined fed fish species, such as salmon, with natural biofilters like mussels and seaweeds on a single farm site, so that fewer of the nutrients originating from the high-energy fish food would be wasted. The seaweed would take some of the nitrogen out of the water, and the mussels would thrive in an environment with such enriched concentrations of food and waste particles. The results of this benign recycling system have been nothing less than superlative. The seaweed, which is used for human food and in health and beauty products, grows fifty per cent faster in the nitrogen-rich fish farm waters. The mussels have similar accelerated growth. Interestingly, this has proven to be a very localized enhancement – a test group of seaweed and mussels at a reference site away from the fish farm did not experience such impressive growth.

There have been some intriguing and unexpected results as well. A dreaded disease in salmon farming is Infectious Salmon Anaemia (ISA), a virus with high mortality rates. To test disease transmittal in a multi-species fish farm, mussels in the laboratory were exposed to the ISA virus. Astoundingly, after a mere twenty-four hours, absolutely no virus was present in either the water or in the mussels. More tests will be done to double check this finding, but it appears that the mussels may filter out some of the virus and have the capability to destroy it. If this is proven to be so, the mussels will add yet another benefit to the fish farm, as a biological form of health insurance to help in the control of this devastating disease.

These are early days for the research, and there are many other avenues to explore. For example, the fish farm ecosystem could be further enhanced with the addition of species that eat particles larger than can be handled by the mussels. These include sea urchins, sea cucumbers and marine worms – all excellent cash crops, with marine worms currently selling for $7 a kilo, as bait. As well there are other seaweeds with economic value and other commercially valuable shellfish such as scallop and oysters to be considered. Another option is to grow organisms with biochemical properties useful for new forms of antibiotics or industrially important compounds. As Robinson explains, “There are probably fifty years of research needed to fully understand the level of complexity in artificially creating a commercial multi-trophic ecosystem.” At present, there are two test sites on existing fish farms in the St. Andrews area. The goal is to add two more per year, to a total of ten.

Underwater shot of IMTA mussels attached to a mussel sock suspended from a mussel raft moored within a salmon farm. Average mussel size is about 50 mm.

There are also regulatory and safety hurdles to overcome. While regulations covering aquaculture in the Bay of Fundy have just been revised to allow mixed species farming, the major concern is consumer safety. The IMTA team is working closely with the Canadian Food Inspection Agency (CFIA) to analyze the mussels and with Environment Canada to monitor the water quality. So far, the CFIA tests, which have looked at levels of heavy metals, pesticides, therapeutants, toxic algae and bacteria linked to birds, are showing the mussels from the IMTA test sites to be perfectly safe to eat. In fact, focus group testing has shown that the mussels have an enhanced consumer value. Not only do they tend to be plumper and sweeter tasting, but they are viewed in the same favourable light as organic foods because of the environmental benefits they bring to aquaculture – and the public is willing to pay more for these attributes.

Another challenge will be to work out the logistics and infrastructure needed for commercialization and harvesting on an industrial scale. A combined species farm requires new equipment and new protocols. For example, the longlines traditionally used for mussel farming don’t work in this new model because of the space they take up and their vulnerability to predation by the eider ducks who over winter in the Bay of Fundy and who have a healthy appetite for mussels. But these are all details to be sorted out. The research has convinced industry that multi-trophic aquaculture is a new idea that will add to their bottom line. Indeed, it’s a win-win proposition, with less waste and more cash crops.

The concept seems so grounded in common sense, but surprisingly the Canadian IMTA teams on both coasts (Steve Cross, University of Victoria, leads the western one) are part of a very small group in the world working on this type of research. And what an excellent leading edge for Canada to be on! As Robinson sums up, “Multi-trophic aquaculture is one of the only workable environmental solutions that we have. It is a truly sustainable system based on ecological principles that have functioned beautifully for eons in nature.”

Last updated : 2007-05-23

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