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     DEPARTMENT OF MARINE RESOURCES

 
The Blue Mussel In Maine

THE RESOURCE

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 depend 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 (MLW). 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 eighties, 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 or 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

Mussel aquaculture involves placing small ("seed") mussels (3/4 to 2 inches long) in an area where growing conditions are optimum and where the culturist has exclusive rights to the harvest. Mussels can be grown to marketable size in 12 to 18 months, and the product is usually of high quality.

There are two methods of mussel culture practiced in Maine - suspended culture and bottom culture. With suspended culture, mussel spat is collected on short ropes hung in the water. Later they are transferred to plastic mesh tubing suspended from floats where they grow until reaching marketable size. These mussels grow very fast and are of the highest quality, but the process is labor intensive and the mussels are vulnerable to storms and ice damage. With bottom culture, seed mussels (1 1/4 to 2 inches long) are collected from dense, wild beds and thinly spread over the lease site. This allows the mussels to increase their growth rate and double their size within a year. This process is less labor intensive than suspended culture, but the mussels are more subject to predation and the harvest is less predictable.

Because marine resources are public property, the right to exclusive access to a resource on any site has to be obtained through a lease. The State of Maine, through the authority of the Commissioner of the Department of Marine Resources, grants aquaculture leases for a period up to 10 years and up to 200 acres in area. Lease proposals are subject to an adjudicatory hearing, which considers the impact of an aquaculture operation on navigation, fishing, access for riparian owners and coastal zoning statutes. As of May 1997, there are 6 mussel leases in Maine that farm a total area of 154.5 acres. This is down from 32 leases over 696 acres in 1986.

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 towards 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 defines seed mussels and their use, describes the seed mussel conservation areas, establishes size limits of mussel drags, and prohibits nighttime harvesting.

 
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