The Blue Mussel In Maine

On the Atlantic coast, blue mussels (Mytilus edulis) are harvested commercially from Maine to Long Island, New York but Maine has historically ranked first in mussel landings. Blue mussels are abundant, bivalve molluscs of the intertidal and shallow, subtidal zone. In Maine they are found in densely populated beds just above and below mean low water (MLW), but are restricted to the intertidal zone in many areas because of subtidal predation. They attach to the bottom substrate with strong string-like appendages called byssal threads, which, in dense beds, can create a thick mat of silt, mud and dead shells held together by the collective byssal attachment of the colony. Within the bed is a rich community of benthic invertebrates including marine worms and crustaceans. These large beds go through natural cycles, increasing in size as silt and shell build up within the bed and then breaking up during major storms.

The commercial quality of mussel beds depends on the stress that the mussels encounter such as lack of food and exposure to air. The weight and flavor of the meats, absence of pearls, and shell appearance are criteria that determine the quality of a bed. Mussels feed by filtering plankton, bacteria, or bits of organic material from the water. The food that they get can depend on the density of the bed, their position within the bed, the strength of the currents just over the bed, or their position above mean low water. Mussels that live under the best combination of these conditions are the most valuable for commercial harvest. Mussel quality also varies seasonally and is a function of the spawning cycle. Just prior to spawning, which occurs during the spring and summer, the meats are best in terms of weight and taste and have the greatest market value.

In Maine, the best commercial mussel beds are found a few feet above and below MLW between Casco Bay and Jonesport. Six of the most productive areas are Casco Bay, Muscongus Bay, Tenants Harbor to Vinalhaven, Stonington to Deer Isle, Sorrento to Mt. Desert Narrows, and the Jonesport area. There is no estimate of the standing crop of mussels in Maine that reflects the condition of the resource at the present time. Earlier surveys estimated the size of the marketable resource at 320,000 bushels (Scattergood and Taylor, 1949) and 544,000 bushels (MARITEC, 1978), but they probably underestimated the resource at the time and the results are now outdated.

The growth rate of Maine mussels varies a great deal depending on circumstances within their immediate habitat. For instance, those in the intertidal zone tend to grow slower than those continually submerged, because food is available only at intervals in the intertidal zone. Under good conditions, mussels can grow about 3/4 to 1-1/2 inches the first year but thereafter the growth rate slows. This is because as a mussel grows it must spend more energy to spawn and sustain itself and therefore there is less available for growth. In general, Maine mussels are relatively slow growing in the wild. It usually takes 7-12 years for them to obtain a length of 2-1/2 inches. Normally, mussels live about 12 years, although individuals have been recorded over 24 years old. Winter mortality above MLW and a host of predators below MLW take a heavy toll on mussel populations.

Wild Harvesting and Processing

Most of the landings in Maine are from wild mussel beds; cultured mussels, at the peak of production during the 1980s, accounted for about 18% of the total landings. Wild mussels can be harvested all year, but most fishing is in the winter when the quality of the meat is best. They are taken by hand with a rake or from a boat with a drag. A license is required from the Department of Marine resources to harvest mussels by either method. A mussel drag is essentially a framed mouth with an attached bag. Across the bottom of the mouth is either a cutting bar or a chain sweep which loosens the mussels as the drag is pulled across the bottom. The mussels are then diverted into the bag. Department of Marine Resources regulations (Chapter 12), restricts the size of mussel drags to an aggregate width of 6 feet 6 inches.

After they are landed, the mussels may be soaked over night to clean the meat and then tumbled to separate them. Tumbling may also be done on board the boat. The mussels are then sorted by size, graded and bagged for shipment to market, or in some cases shucked and the fresh meats sold.

Aquaculture

There are two methods of mussel culture practiced in Maine — suspended culture and bottom culture. With suspended culture, mussel spat is collected on ropes hung in the water at spat collection sites. They are then sorted and transferred to grow-out ropes by wrapping a biodegradable socking material around the mussels and rope. The socking material degrades as the mussels attach themselves to the rope with byssal threads, where they remain attached until harvest. The ropes are suspended from floats, rafts or horizontal longlines, and are usually protected by predator nets or housed within modified fish pens. These mussels grow quickly, but the process is labor intensive, and the mussels are vulnerable to storms and ice damage. With bottom culture, seed mussels are collected from dense, wild beds and spread thinly over the lease site to allow the mussels to increase their growth rate. This process is less labor intensive than suspended culture, but the mussels are more subject to predation.

The exclusive use of public waters for aquaculture must be obtained through a lease. The State of Maine, through the authority granted to the Commissioner of the Department of Marine Resources by the Legislature, may issue aquaculture leases for a period of up to 20 years and a maximum size of 100 acres. Lease proposals are evaluated with respect to their potential impact on navigation, fishing and other waterborne uses, access for riparian owners, other aquaculture uses, the existing ecosystem and habitat, and public facilities. An adjudicatory hearing may also be required.

As of February 2020, there are 4 scientific and 28 commercial leases approved for the culture of blue mussels in Maine, with a total area of 350 acres. Of these, 14 reported a commercial harvest in 2018, totaling 2,126,250 pounds and valued at $3,234,580.

Management

Mussel regulations were implemented in 1988 by the Department of Marine Resources in response to concerns within the industry and legislature that the intensity of the fishery that existed at that time was leading to resource problems and conflicts between users. One of the major problems was the significant demand for seed mussels by the aquaculture industry. There was a fear that recruitment to the prime wild beds might be impaired if the seed was heavily harvested and transferred to lease sites. The solution was to find an alternate source of seed for the aquaculture industry. To this end, the mussel regulation established four "seed mussel conservation areas", from which only seed-size mussels may be removed for growout. A permit issued by the Department of Marine Resources is required to remove any mussels from the conservation areas.

The mussel regulation (see Chapter 12) defines seed mussels and their use, describes the seed mussel conservation areas, establishes size limits of mussel drags, and prohibits nighttime harvesting.

Landings and Value

Visit our Historical Landings Page, for recent and historical annual landings data (pounds and value) for Maine blue mussels (includes both wild-harvested and cultured).