September 22, 2011
by Dr. Heather Deese and Catherine Schmitt
Some surprising numbers: of the seafood Americans currently eat, more than 50 percent is farm-raised, and nearly 84 percent is imported. But compared to other nations, we don’t eat that much seafood, and the most recent federal dietary guidelines recommend that Americans more than double their current average seafood consumption because of the health benefits.
If we all decide to start eating twice as much seafood starting tomorrow, where will we find the fish?
The National Aquaculture Act of 1980 and federal aquaculture policy encourage the development of aquaculture in the U.S., based on the assumption that future increases in supply are likely to come either from foreign aquaculture or increased domestic aquaculture production, or some combination of both.
Realizing that increasing demand for seafood can’t be met by projected stocks of wild fish, seafood scientists and business leaders continually look for ways to advance and modernize marine aquaculture. In Maine, through funding by NOAA Sea Grant, scientists from the University of Maine and Cooke Aquaculture deployed a mussel raft, one hundred meters in circumference, at one of the company’s salmon farms off the Washington County coast in late August. This experiment, designed to test how water quality and animal health are affected when both species are raised within the same aquaculture site, is the first in Maine to focus explicitly on whether integrated multitrophic aquaculture (IMTA) can be mutually beneficial to farmed species.
The mussels, an anticipated 60,000 pounds, will be ready to harvest in 12 to 18 months. In the meantime, the young, quarter-inch to half-inch seed mussels are encased in cotton mesh “socks” that hold the animals in place until they begin producing byssus threads that help them adhere to a central rope. The 20,000-pound seed lines hang, like garlands on a Christmas tree, from five concentric floating circles of a specialized raft made from old salmon cages.
Dr. Ian Bricknell, director of the Aquaculture Research Institute at the University of Maine, and his students will be conducting parallel research on disease ecology in the laboratory to look at how the mussels and salmon influence each other’s health.
While people have experimented with raising multiple species, or polyculture, in Maine before, IMTA goes beyond simply producing more than one species to seeking mutually beneficial relationships that result in a more sustainable business and a better end product. The idea mimics what happens in the ocean naturally, where species share habitat and influence each other.
In the UMaine/Cooke experiment, the partners are hoping that the presence of mussels may help to control damage inflicted on the salmon by infectious anemia virus and sea lice, a costly parasite. Mussels are filter-feeders: they screen out food particles from the surrounding water. Bricknell and post-doc Sally Malloy recently found in a laboratory study that as mussels filter seawater, they can consume copepodids, the planktonic and infectious stage of sea lice. If this effect is also seen in the field, then salmon farmers will have a new biological control method for managing sea lice, a tool the industry has been seeking for a long time, according to Sebastian Belle, director of the Maine Aquaculture Association.
Why these two species? Salmon is Maine’s second-most-valuable fishery after lobster, and the local mussel market has room for growth. While Maine’s wild mussel harvest is much larger than production of cultured species, farm-raised mussels fetch a higher price because of their longer shelf life and higher meat yields. Mussels also take up excess fish food and nutrients, a service that maintains water quality while enriching the mussel meat with heart-healthy omega-3s. And mussels grow faster at IMTA sites; yields on New Brunswick salmon farms are 25 percent greater than on a typical single-species mussel farm.
Similar IMTA operations elsewhere in the world incorporate various seaweeds, and Cooke has been raising mussels and kelp side-by-side with salmon for years in New Brunswick. The University of Maine will be expanding research and trials to seaweed and other species in the future.
“IMTA is one of our key research themes,” said Anne Langston, associate director of the Aquaculture Research Institute. In addition to expanding to new species and studying biosecurity and health, future aquaculture research needs include nutrient cycling, harvesting strategies and market development.
In addition to testing whether the species can be grown together in Maine for commercial production, the research funding includes support for related industry training and management considerations to get more salmon farms integrating other species. For example, cross-training might be needed to educate fish farmers about mussels and vice versa. And as a producer of seafood, Cooke is of course interested in succeeding in the billion-dollar global salmon industry.
The hope is that the growing demand for seafood could be partially satisfied by safe, locally-produced fish, sea vegetables and shellfish that sustain an industry and a way of life.