With aquaculture as a rapidly growing source of food across the globe, UNH seeks to explore the cutting edge of aquaculture technology to ensure a responsible and sustainable future for the industry. Much like land-based agriculture, aquaculture can be done in ways that maximize the economic and health benefits to the community, while potentially benefiting the environment. One such technology is Integrated multi-trophic aquaculture, or IMTA. This method addresses concerns about nutrient loading in aquaculture by utilizing additional farmed products to remove excess nutrients, which typically enter the environment in the form of fish waste. In large fish farms, the waste from the fish add nutrients to the water, and in areas without much water flow, or areas that already have a high nutrient load, this could degrade water quality. With IMTA, additional products are grown with the fish, such as algae and shellfish, which will grow by removing and absorbing the excess nutrients. In NH, Dr. Michael Chambers with NH Sea Grant and the UNH School of Marine Science and Ocean Engineering have explored this practice in a model named AquaFort, which raises steelhead trout in net pens with sugar kelp and blue mussels on lines outside of the nets.
The IMTA system is sized so that the extractive species, such as mussels and kelp, absorb an equal amount (or more!) of the solid and dissolved nutrients as produced by the high valued fed species like steelhead trout. This effectively produces a system that could enhance the environment.
Species profiles
Steelhead trout (Oncorhynchus mykiss)
This salmonid species is native to the North American West Coast but has been stocked by state and federal hatcheries in rivers and streams for decades in the East for recreational anglers. Steelhead trout are diadromous fish, meaning they use both freshwater and saltwater habitats to complete their lifecycle. In freshwater, they are referred to as “rainbow” trout. When they get to salt water, they are then referred to as “steelhead”. The steelhead raised in AquaFort are hatched locally at the Sumner Summer Brook Trout Farm in Ossipee, NH, and transferred to a saltwater pen when they are close to 200 g. They can grow from 200 g to 4 kg in less than a year. These fish have a high market value, and show great potential to be an economically important fish in U.S aquaculture. These fish are sold to local seafood markets in Portsmouth such as Seaport Fish, Row 34 in Portsmouth and Sanders Fish Market.
Blue mussels (Mytilus edulis)
Blue mussels are a common bivalve species in North America. These shellfish can be farmed on various submerge or vertical ocean deployed systems. Since mussels are filter feeders, they take water in through their siphon, consume the organic material in the water, and pump out the clean water. This makes them a great co-species to raise with steelhead trout, as the mussels are able to consistently filter water through most conditions. When raising mussels in the North Atlantic, farmers must be aware of shellfish closures and restrictions, and be prepared for predation by birds, especially eider ducks. The mussels raised in AquaFort are wild mussels, meaning they are collected as wild larvae. This is done simply by deploying “fuzzy” rope, which provides extra surface area for larval mussels to easily settle on. After some time they grow on the line and begin filtering nutrients from the water.
Sugar kelp (Saccharina latissima)
Sugar kelp is a macroalgae species that is also common throughout the North Atlantic. This species is ecologically important because it provides habitat and nutrients for countless marine organisms. Farming of kelp has grown tremendously due to its nutritional benefits for people, has potential as feed for livestock and perhaps as a basis for producing biofuel. In AquaFort, this crop absorbs dissolved nutrients from steelhead trout. It also grows best throughout the Winter and Spring and therefore complements many fishing industries. Sugar kelp can come from recently selected strains, or wild strains that are grown on a seed line in a closed system. After it sets on the twine, it can be deployed in the farm. The sugar kelp found on AquaFort comes from Atlantic Sea Farms in Biddeford ME. When it’s ready to harvest, look for it at the Portsmouth Brewery, where it becomes an ingredient in their “Selkie” ale.
The AquaFort Structure
With the UNH AquaFort, all three species are raised on a single platform system. The platform has two separate bays, which each hold a net. The fish school inside the net, and mussel lines and kelp lines hang around the outside, creating a biological “curtain” to ensure they maximize their impact on the fish waste. The platform itself is a floating frame made with HDPE, and it is anchored on two sides to prevent it from moving in the changing tides and current. The fish need to be fed and monitored daily, with their welfare and growth being priorities. The mussels and kelp thrive without much interference, and offer habitat for wild species like lumpfish and gunnel fish.
The AquaFort system concept: One structure for three seafood products.
Overhead view of the IMTA model.
Where IMTA stands now
Trialing multiple seasons of IMTA with steelhead trout, kelp, and mussels has yielded exciting results. Not only does this strategy remove excess nutrients from the fish, but the kelp and mussels have sequestered additional nitrogen from the environment. This indicates that utilizing IMTA in regions that nitrogen and other nutrients are a concern might benefit the quality of the water, and ultimately help the environment.
The research on integrated multi-trophic aquaculture continues. Future aspects will look at land based IMTA, varying the species grown in AquaFort, and looking at expanding the AquaFort model to other parts of the United States, and beyond. Please check back to see additional publications and updates on the future of IMTA.
