Farmers in Puget Sound recently concluded a multi-year experiment, placing an oyster and mussel farm near an active salmon farm.
The result? Fish poop from the farm helped the oysters nearby grow bigger than shellfish located further away.
Oysters at Cypress Island received significant nutritional and growth benefits from placement near the salmon net pens. Oysters closer to the net pens experienced consistently higher growth and were able to take advantage of fish feces produced by the site.
Integrated Multi-Trophic Aquaculture is not new, but not many people are doing it. We are glad to see some salmon farmers on the Pacific Coast attempting it; we would love to see B.C. salmon farmers attempt something similar.
Farmers on the East Coast of Canada, in the Bay of Fundy, are experimenting with growing shellfish and salmon in close proximity. They have been doing it for more than a decade.
There have been some experiments done in B.C., most notably by Dr. Steve Cross from the University of Victoria. His work shows that Integrated multi-trophic aquaculture is possible in B.C. and could be economically viable.
And there don’t appear to be any major reasons why it couldn’t work on a large scale in B.C.
The biggest concern with integrating shellfish production with a salmon farm is the risk of disease. Salmon farmers are understandably concerned that shellfish could incubate diseases and pass them on to the farmed fish nearby. But in 2008, the International Council for Exploration of the Sea’s Working Group on Environmental Interactions of Mariculture released a report showing that the risk of disease is low.
In fact, the report pointed out, having shellfish nearby could be a benefit. Certain species have been proven to destroy the ISA virus (present on the East Coast of Canada) and also to eat sea lice.
Diseases and parasites are often one of the first concerns that are raised in the implementation of IMTA. It is thought the addition of additional species may help to either harbour or transmit diseases to the primary fed crop (e.g. salmon).
Some of these objections are the result of a monoculture perspective. In actual fact, if the IMTA species used are endemic to the area, then they are usually already present on the site in close proximity to the animals as part of the fouling community. Therefore, it is not a case of presence or absence, but rather one of dose threshold and whether or not the species are capable of retaining or transmitting the disease.
For one disease, Infectious Salmon Anemia (ISA), the blue mussel Mytilus edulis) has been shown to destroy the virus (Skar and Mortensen, 2007). This has been verified in subsequent experiments (S. Robinson et al, in prep.).
There is also potential for positive interactions to occur for parasites. On salmon the sea louse (species?) can cause significant losses for the salmon farming industry. Since mussels have been documented to eat nauplii, it may be possible for mussels to reduce the infection of salmon by sea lice by the incorporation of mussels into the salmon production site.
We would love to see B.C. salmon farmers invest more in exploring and testing this production system. It holds huge potential, and could put B.C. farmers at the head of the pack when it comes to sustainability and farming an environmentally-sustainable product.