IMTA: Mother Nature's Tetris

Courtesy of NOAA

The fisheries are in trouble. We (humans) having been taking far too many fish out of the sea for too long. Now, populations of many of the different types of fish we eat are at risk of collapsing. If we continue taking more and more fish from the sea, fish populations may get so low that the fishes can never recover, as we are witnessing with the Atlantic cod population. The trouble is that over one billion people rely on fish as their main source of protein. As the amount of fish people have been able to catch levels off and the human population continues to grow, fish farming, or aquaculture, has significantly increased production to meet the human need for fish.

Aquaculture now produces about 40% of all aquatic food in the world, but there are a few problems with it. First, aquaculture relies on wild-caught fish to feed the farmed fish. Most of the fish species being farmed are predatory and therefore eat other fish. Many of the businesses that provide fish feed are putting unsustainable fishing pressure on wild stocks. This means that aquaculture is not necessarily taking fishing pressure off wild stocks so much as moving that pressure on a different wild stock.  The caught fish are ground up with other ingredients to make fish meal, which is packaged in a pellet form. These pellets are then fed to the farmed fish. This leads us to the second problem: excess fish pellets, as well as all of the waste from the high density fish pens. Though it has been getting better in recent years, some of the pellets that the farmed fish can’t eat fall through the nets and accumulate on the bottom of the ocean. This, with all of the feces from the farmed fish, create high nutrient levels that can harm the local ecosystem.

There is one type of aquaculture system that attempts to address these issues, integrated multi-trophic aquaculture, or IMTA. IMTA is essentially the farming of different species that are all working together. There is the main fed component, usually fish, being grown with bottom feeders that will eat the large waste particles and excess food pellets, usually urchins or sea cucumbers, some filter feeders that can eat the smaller waste particles, such as mussels, clams, oysters or scallops and finally some seaweeds that can filter the ammonium, or urinary waste from all of the animals. The idea is that the combination of animals and seaweeds allows for increased growth of species while cleaning up all the waste created by the fish. Though IMTA still uses fish pellets for feeding the fish, the farm is able to produce more than just the fish for the same amount of pellets used. 

Cascadia SEAfood was founded by Dr. Stephen Cross who operated an oyster farm he had started in Kyuquot Sound, which is off the west coast on the northern side of Vancouver Island. When Dr. Cross began applying for permits to create an IMTA system in BC, he essentially had to create the permits for the system as it had not yet existed.  In the years since, Dr. Cross has used his farm as a research facility for IMTA systems and only recently has his farm moved into commercial production of his seafood products. Cascadia is actively growing sablefish, oysters, scallops, kelp, nori, sea cucumber and sea urchins which are sold to markets in Tokyo, Los Angeles and Vancouver. 

Courtesy of DFO

There are currently no indications that the feed required to produce the sablefish has decreased in Cascadia’s IMTA system. However, the IMTA farm is able to produce more per kilogram of harvested fish than a traditional fish farm, for the same amount of feed used. Apparently for every 1 kg of sablefish harvested, approximately 63 oysters, 5 scallops, 1.5 sea cucumbers and 1 kg of kelp can be annually harvested with no additional additives. So although wild fish are being used to feed sablefish at Cascadia, the wild fish used as fishmeal are used more efficiently and produce more consumable protein than traditional aquaculture systems.

Does IMTA have a terrestrial equivalent? In some examples of small scale crop rotation, a farm will rotate multiple crop types through a field in order to use the full range of nutrients the soil contains. This sort of rotation often uses animal manure during one rotation, while not growing a crop, in order to re-supply the soil with nutrients necessary for growth and reduce or eliminate fertilizer use. Similarly, IMTA farms produce fish, and their waste and extra nutrients, are then used to grow other aquatic products. The use of animal wastes and abundant nutrients in both terrestrial farming and aquaculture allows for these farms to reduce their ecological impact.

So the question remains, can IMTA aquaculture systems make money? For now the farms using IMTA systems for commercial purpose are relatively small scale farms that are located close to shorelines.  Many larger commercial aquaculture ventures are located in more remote locations with strong currents where IMTA won’t be beneficial as the nutrients will be washed away before they can be absorbed. Most large scale operations also have farm set ups and designs that are not very compatible with IMTA. As a result, IMTA is less attractive as a financially viable option to some of these large scale producers. Despite potential setbacks, many large scale producers are interested in investing in IMTA systems, but are waiting to see if small scale producers can produce a larger profit from IMTA techniques over traditional aquaculture.

IMTA, as seen through Cascadia’s model, is a hopeful alternative to traditional aquaculture, as it uses sustainably caught wild-fish to feed the fish in the system, and it uses the fish waste and extra nutrients in the system to produce more aquatic products. Although it is in the beginning stages, Cascadia SEAfood is an example of a working IMTA system, and can be used as a model for other farms. Small-scale farms seem to be ideal for current IMTA systems, as larger farms may face challenges with finding the right location to set-up an IMTA system. Despite the challenges for large scale aquaculture and the economic uncertainty around IMTA, Fisheries and Oceans Canada lends support to IMTA, in encouraging greater environmental stewardship while increasing economic benefits for farms and local communities. As the benefits become more widely known, the adoption of IMTA can increase, and this can hopefully reduce the pressure on wild fish populations.

Courtesy of Cascadia SEAfood