Blue Mussel Culture
Photo Caption: MV Ocean Reporter on mussel line station off Rockport MA.
Long Line Mussel Culture on Cape Ann, Massachusetts
Shellfish culture along the coast of Massachusetts is centered within the intertidal zone. For decades growers have concentrated on hard-shelled clams and oysters primarily on Cape Cod, as well as scallops around the Islands of Nantucket Sound and recently soft-shelled clams both North and South of Boston. Coastal waters, however, are crowded with numerous user groups making access to acceptable shellfish areas increasingly difficult. In many approved areas space is often the limiting resource for shellfish aquaculture. Thus subtidal culture of shellfish is a potential alternative.
Over the past 2 years, staff at the NEMAC (Northeastern Massachusetts Aquaculture Center) has built upon work done elsewhere and investigated the potential for culturing the blue mussel, Mytilus edulis, sub-tidally.
Experimental long-line set-ups have been deployed off of Cape Ann to evaluate the potential for growing mussels on long-lines.
Methods
Mussel seed (mean size 6.2 mm) was collected and stocked onto six dropper lines. Each line was 2 m long and stocked at a density ~ 1000/m using standard cotton socking and core “fuzzy” rope. In July 2006, these lines were deployed in 10 m (MLW) of water about 90 m off Hodgkin’s Cove in Gloucester, Massachusetts The lines were suspended from floats 6 m below the surface water to avoid fouling with boat traffic (not clear if floats or lines were 6 m below surface). The set-up was designed to keep the mussel lines 5 m off the bottom to limit exposure to potential predators, especially crabs and sea stars. Mussels were monitored monthly for a period of 15 months. Gear inspections were conducted by divers and video recordings were made.
Results
Despite having one anchor rope severed and the subsequent loss of an end float and a mooring block in February 2007. Significant mussel growth and survival were noted during the study period. Mussels grew to a mean size of 61.1 mm regardless of stocking size over the 15- month study.
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"Socked” mussels deployed on long lines |
View of mussel long lines off Rockport, MA |
Discussion
Lines that escaped damage were laden with mussels, weighing as much as 10 kg/2m rope. With the limited success exhibited in rapid growth and most of the mussel loss seemingly attributable to gear trouble, we continue to see growing interest in the local fishing community in slowly expanding our efforts. Plans are currently underway to deploy additional long lines in deeper water to assess further and garner interest in the commercial viability of blue mussel culture in the waters off of Cape Ann.
The potential advantages of long-line shellfish production in offshore waters are many:
- Limited impact on local habitats.
- Complement shore-based shellfish harvest.
- Multiple lines may be deployed in coastal and off-shore sites with minimal impacts to other maritime activities, such as other fisheries and recreation.
- Fishers may supplement traditional fishing activity with open water shellfish harvest, providing a new way to use their boats.
- Lines can be seeded with hatchery-reared and wild caught seed, reducing fishing pressure on natural shellfish populations.
- Filtering activity of mussels can enhance water quality by removing excess organics.