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at the time and the results are now outdated.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.
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.
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.
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.
