Integrated Multi-Trophic Aquaculture

Integrated Multi-Trophic Aquaculture
Neither monoculture nor polyculture, IMTA is a technique that involves utilizing the waste from a fed species to feed other species kept in the same environment. This creates a balanced ecosystem with enhanced profitability and stability as well as better environmental sustainability. While monoculture is the farming of a single species, and polyculture is the farming of multiple similar species, IMTA incorporates multiple species from different nutritional or "trophic" levels in the same system. For example, a farm could incorporate shrimp, which are fed by the farmers, with seaweed and shellfish, which would make use of any waste nutrients from the shrimp.

Concerns
Some issues have been raised concerning the potential for contaminants being passed from one species to another. However, there has so far been no noticeable levels of heavy metals, pesticides, or other toxins. Worries that mussels grown near salmon farms could have a fishy taste have also been allayed. In fact, their meat yield is significantly higher as a direct result of the increased nutrients from the salmon pens.

Canada
There are two major IMTA projects in Canada.The Bay of Fundy project is a collaborative effort involving industry, academics, and government. It incorporates Atlantic salmon, blue mussels, and kelp working together in a self-contained ecosystem. The Pacific SEA-lab research initiative propogates sablefish, scallops, oysters, blue mussels, urchins, and kelp in a more complex system.

More Info:
http://www.dfo-mpo.gc.ca/aquaculture/sheet_feuillet/polyculture_e.htm
http://www.springerlink.com/content/j416160726015891/
http://www.aquaculture.ca/files/species-multi-trophic.php

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Bluefin Tuna

Bluefin Tuna can grow up to 3/4 of a tonne, and can swim at speeds reaching 50 km/h. However, they aren't beyond our reach. Bluefin fishermen use every resource available, including huge engines, spotter planes, and harpoons. Their migration routes are so predictable that fishermen know just where to catch them. In the Western Atlantic, since the mid 1970's, the bluefin population has declined by more than 85%. Scientists are calling for a total ban on fishing for bluefin, but many fishermen refuse to accept the fact that the populations are in danger at all.

Until fishermen realized that they could airlift these fish to Japan, bluefins were only worth a few cents a pound. Now, a single fish can sell for upwards of $25,000, occasionally going for more than $200,000 when the market fluctuates. The Japanese are by far the biggest importers of bluefin tuna in the world.

Japan is already a leader in aquaculture, and now they're even trying to raise bluefin tuna in captivity. Most farmed tuna are caught in the wild, then fattened up in ocean pens. Unfortunately, they are very sensitive to changes in water temperature and sunlight, and they need to be fed huge amounts of small fish, which would otherwise be a valuable protein source for the poorer people in Asia.

For now, tuna farming is only marginally better than catching them in the wild, environmentally speaking. However, methods are always improving, and hopefully technological and ecological capabilities will be developed to the point that it is truly sustainable.

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