UNH-led team designs aquaculture raft to provide four-season source of seafood and sea veggies

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The Piscataqua River is home to a new piece of equipment: an aquaculture raft intended to provide a four-season source of local fish and shellfish, increasing revenue for struggling N.H. fishermen while removing excess nitrogen from the water.

The raft, designed by a University of New Hampshire team including graduate student Corey Sullivan (UNH ’14) and UNH ocean research engineer Matthew Rowell (UNH ’13G), will house steelhead trout, blue mussels and sugar kelp potentially valued at $70,000 annually. This equipment provides a much-needed upgrade to older, smaller aquaculture rafts currently in use on the river and will help ease the permitting process for fishermen who want to get involved in growing these species for sale in local markets.

UNH researchers, N.H. commercial fishermen and an in-state manufacturing facility collaborated for almost a year to design the raft, which was deployed in the river on Aug. 24, 2015. Hanging from a crane — its appearance like a giant plastic UFO in mid-air — the 41’x22’ raft was gently lowered to the river next to the UNH Pier in New Castle, N.H.

Sullivan watched the deployment intently from shore, scanning the water surface for bubbles that would indicate a raft leak somewhere; to his relief, none appeared. “I was definitely holding my breath,” he said with a laugh.

Large aquaculture raft is lowered by crane into the river.

Above: Corey Sullivan (UNH '14) watches intently from shore as the new aquaculture raft he helped to design is lowered by crane into the water by the UNH Pier in New Castle, N.H.

Prior to deployment, the double-bay, 7,500 pound raft was transported in two halves on a flatbed truck from its manufacturing facility, JPS Industries, in Bristol, N.H. When it arrived at the pier, it was lifted off the truck and placed on the pavement, where the two halves were then bolted together. Among the individuals helping out were project leaders Rob Swift and Barbaros Celikkol (UNH professors of mechanical and ocean engineering) and Michael Chambers (NSHG/UNHCE marine aquaculture specialist). Once assembled, the raft was then lifted into the water and moored to the pier where it now awaits additional construction to accommodate a walkway around the edge and a framework to hold the fish pens and mussel lines. 

“It was surreal to see it come together, to see the full scope of it in held up the air by that crane after looking at it for so long on a computer screen,” Sullivan said. “I was really happy when it sat just how I wanted it to sit in the water,” he added.

Half of large aquaculture pen is lowered to ground via a crane.

Above: One side of the new aquaculture raft is lowered to the ground for assembly.

Ten N.H. fishermen have raised steelhead trout in the four old pens at the mouth of the Piscataqua River for the past three years for sale in local markets. The new raft design will allow two 15’x15’ underwater nets to hang from the raft side by side, offering more space to grow the species and improved stability in rough seas during winter months. The raft base is constructed from high-density polyethylene that is relatively flexible; it is critical for the materials to withstand strong currents and wave action during rough winter storms, said Swift.

Sullivan, Chambers, and 2015 Doyle Fellow Megan Peavey (UNH ’16) are currently constructing the wooden-planked walkway on top of the raft and attaching the stanchions to the frame. Construction should be finalized in the coming weeks, and the raft will then be towed out to the UNH aquaculture site in the mouth of the Piscataqua River near Fort Constitution. Chambers hopes to train more fishermen and aquaculture entrepreneurs from N.H. and Maine in the upcoming year. The raft was designed to hold up to two tons of steelhead trout, six tons of blue mussels and one ton of sugar kelp.

Man and woman work on attaching wooden planks to floating raft.

Above: Michael Chambers and Megan Peavey (UNH '16) work on constructing the walkway for the new aquaculture raft at the UNH Pier in New Castle, N.H.

Young man helps construct wooden walkway on floating raft.

Above: Corey Sullivan (UNH '14) helps with the construction of the walkway on top of the raft. Pictured behind Sullivan are two old aquaculture rafts that will be replaced by this larger improved version.

This project is an example of integrated multi-trophic aquaculture (IMTA), whereby two or more species that occupy different parts of the food chain are grown in the same area. The advantage of employing IMTA over traditional aquaculture methods comes by way of waste products; fish excretions can be used as fertilizer or food for the other species growing around the raft.

“We’ll put at least 100 mussel lines in the water hanging from this raft,” said Michael Chambers, NHSG/UNHCE marine aquaculture specialist. “This will allow for the mussels and kelp to extract the nitrogen excreted by the trout into the water column to create a neutral footprint; depending on how many lines we put in, we may be able to remove more nitrogen than the trout excrete,” he added.

This project is a "dream come true" for Chambers and Hunt Howell, UNH professor of biological sciences, who have been exploring IMTA for the past four years with the old cage infrastructure.

Historically, it has been difficult for fishermen to obtain the necessary aquaculture permits due to concern over pen-raised fish waste adding nutrients to waterways that already have too much nitrogen. This has been a major impediment to the growth of the aquaculture industry in New England, Swift said, but IMTA is helping to change that.

“In addition to being environmentally sustainable, the use of IMTA methods will expedite the process for fishermen to obtain permits,” Swift said. “This technology is readily transferable to other New England states in its present form, and the concept is transferable to all U.S. coasts and worldwide,” he added.

Funding for this project was provided by a grant from the NOAA Saltonstall-Kennedy Grant Program and by N.H. Sea Grant. For more information, please contact Michael Chambers at michael.chambers@unh.edu or Rob Swift at mrswift@unh.edu.

N.H. Sea Grant promotes the wise use, conservation and sustainable development of marine and coastal resources in the state, the region and beyond. Located at the University of New Hampshire, NHSG is part of a national network of programs located in our coastal and Great Lakes states as well as in Puerto Rico and Guam.



Rebecca Zeiber, N.H. Sea Grant Science Writer