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SHELLFISH SPECIES
GIANT SCALLOP or Sea scallop
Introduction
The giant or sea scallop, Placopecten magellanicus, is found in the eastern
North Atlantic Ocean ranging from the north Gulf of St. Lawrence and northern Newfoundland
to North Carolina. Giant scallops are a highly valuable shellfish commercially,
for instance, 57,151 tonnes of wild scallops were landed at a value of $82 million
in 2005. Consumer demand for fresh, high quality scallops make scallops an attractive
species for development. New technology, scientific research and development and
innovative culture methods have increased the viability of the scallop industry
in Canada. Sea scallops are predominantly cultured in Nova Scotia and Quebec. In
2005, 11 tonnes of cultured sea scallops were produced in Canada at a value of C$91,000.
Of note, there was some early experimentation with the culture of bay scallops,
Argopecten irradians, an introduced species to Atlantic Canada. However,
interest in culturing this species in this region has declined. The Iceland scallop,
Chlamys islandica, also exists in parts of Atlantic Canada and there has
been minor interest in culturing this species on the lower north shore of Quebec.
In British Columbia, there are successful farming operations for the Japanese scallop,
Patinopecten yessoensis. In 2005, 226 tonnes of cultured Japanese scallops
were produced in Canada at a value of approximately C$1 million.
Basic description
The scallop is possibly best known for its beautiful and distinctive shell. Scallops
are bi-valve molluscs, the type that have a hinged two-part shell. Scallop shells
are fan-shaped and are roughly equal in diameter, the top shell being slightly more
convex than the other. Externally, the shells have radiating ribs or grooves and
concentric growth rings. Near the hinge, where the two valves (shells) meet, the
shell is flared out on each side forming small "ears". The upper shell is reddish-pink
in colour while the lower shell is white or cream in colour. Inside these shells
is the "meat" (the abductor muscle), which is the part of the scallop commonly eaten
in North America. The meat is white, firm in texture and has a mild flavour.
Cultured scallops have a two to three year grow-out cycle. Growth rates vary
with location and are dependent upon temperature and food supply. Cultured scallops
are well adapted to environmental conditions in Atlantic Canada as they are native
to that region. Farmed scallops are typically harvested when their shell is 50 to
90 mm (2-3.5 inches) depending on market demand. Scallops are either sold live in
the shell, like mussels and oysters, or are shucked and the meat is sold fresh or
frozen.
Background
Experimentation with scallop farming began in Canada in 1971 in the community
of Port au Port, Newfoundland and Labrador. The commercial scallop farming industry
developed in earnest in the early 1990s. By 1994, there were sea scallop farming
operations in all five Eastern provinces. Currently there are commercial-scale operations
only in Quebec and Nova Scotia. For a comprehensive description of the history of
sea scallop culture in eastern Canada, consult Couturier et al. (1995) (full
bibliographical reference in the For More Information section below).
Production
Scallop farming is a process that goes through four steps: one, spat or seed
procurement; two, intermediate culture; three, final grow-out; and four, harvesting
and marketing.
Scallop farmers require a reliable source of spat. Spat refers to fertilized
shellfish larvae that has either been cultured from broodstock in hatcheries or
obtained from the wild using artificial collectors, which usually consist of "onion"
bags filled with monofilament gillnetting. Spat collectors are suspended in the
water column in an area that has a local population of sea scallops. The bags are
generally deployed just after the scallops have spawned, which generally occurs
from mid-summer to autumn. Sea scallop larvae float through the water column for
about a month after which they ‘look’ to settle on uneven, rough surfaces such as
the monofilament gillnetting within the spat collectors. The spat collectors are
left in suspension between 9-11 months during which the scallops are large enough
(10 mm) so they will not fall through the mesh bags or pearl nets, and their shells
are hard enough to be handled and sorted.
Intermediate culture, which typically involves the use of pyramidal shaped pearl
nets, trays or small mesh lantern nets, is a necessary step for raising all scallop
species for increasing both survival and initial growth. When scallops are harvested
from spat collectors, they are too small for suspension or bottom culture – both
potentially leading to escapement or predation. Intermediate culture of juvenile
scallops consists of growing scallops in pyramidal or conical shaped "pearl" nets
which are suspended on long lines in the ocean until they are large enough for the
final, grow-out stage. This step takes approximately one year, when their shells
reach 40-60 mm in diameter.
Scallop farmers can use several different types of techniques to grow-out juvenile
scallops to market size including pearl nets, lantern nets (a multi-tiered accordion
style net), trays, large cages, ear hanging (where a hole is drilled in the "ear"
or auricle of the scallop and they are hung on suspended ropes) or bottom culture
(where scallops are seeded directly on the bottom of the ocean). The most predominant
method is the use of Japanese lantern nets or some variant on this design. Scallops
are sorted by size and loaded into the different levels and the nets are suspended
in mid-water. As the scallops grow they are thinned into larger mesh nets. The farmer
must balance two needs: to have a mesh net that is just small enough to prevent
scallops from escaping, and large enough to maximize water exchange. Growth varies
from site to site, however scallops grown in suspension systems take six months
to two years to reach market size, whereas bottom grown scallops require a further
two to three years.
Like all bivalve shellfish species, scallops are filter feeders that consume
nutrients that naturally exist in the water column (microscopic algae and plankton).
Scallops are sensitive to water quality and fluctuations in water temperature and
motion. Scallops prefer to be still, they don’t like to be jiggled, therefore the
longlines are suspended just far enough below the surface to avoid wave action in
the ocean. The optimum culture depth for a particular location will depend on the
distribution of the food in the water column and the depth to which wave action
will impact the suspended culture gear. Scallops grown in suspension systems are
monitored regularly and transferred into larger mesh nets as they grow because scallops
do not like crowded conditions. This monitoring also allows the farmer to regularly
assess the health of the animals, extract mussels (and other fouling organisms)
that may be binding the scallops together from byssus threads, and remove any predators,
like starfish, that manage to get inside the nets.
A diagram illustrating suspended long-line scallop culture using seedbags, lantern nets and pearl nets is available on the Nova Scotia Ministry of Agriculture website in a document entitled, "Unit 3 Aquaculture: A Look at Fish Farming" (page 12, available in English only).
Canadians can enjoy fresh scallops twelve months of the year. Cultured scallops
complement the supply of oysters at your local seafood counter when wild, commercially-harvested
oysters are not available. Harvest times of cultured scallops are contingent on
the type of products to be marketed that require different sized scallops (50-90
mm) to be available throughout the year. Farming methods and practices are adjusted
to ensure a staggered supply to meet retail demand. The main constraint to larger
scale scallop development is that it is a capital and labour intensive venture with
relatively long grow-out period (three years from egg to minimum harvest size).
Several economic analyses have been conducted and culture techniques have improved
over the last decade to identify the best conditions to create an economically viable
industry.
**Many thanks to Jay Parsons and Shawn Robinson for their permission to reproduce
generous portions of their work recently published in Scallops: Biology, Ecology
and , 2nd Edition (2006) for this species profile. For the proper bibliographical
reference of this work, please see the For More Information section below.
DFO Research Activity
Biotechnology to Help Breed Better Scallops
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DFO researchers are working to improve the quality of scallop meat by
developing triploid scallops for aquaculture.
The following studies are funded through DFO’s
Aquaculture Collaborative Research and Development Program:
For more information
Scallop farming in British Columbia (BC)
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Scallop farming has been underway in BC for 10-15 years. Although the potential
for a large viable culture industry is significant, the production of
farmed scallops remains relatively small. Scallop farmers in BC have
achieved success in the development of the Japanese scallop,
Patinopecten yessoensis, which was adopted for culture in BC from
Japan. Recently, a superior hybrid of the Weathervane (native to BC)
and Japanese scallop has been developed for culture in British Columbia
For more information related to scallop farming in BC, please read the
species profile prepared by the BC Shellfish Growers Association
(2005).
Parsons, G.J. and Robinson, S.M.C., 2006. Sea Scallop Aquaculture in the Northwest Atlantic.
In S.E. Shunway and G.J. Parsons (Eds.), Scallops: Biology, Ecology and
Aquaculture, 2nd Edition. Developments in Aquaculture and
Fisheries Science, Vol. 35. Elsevier, The Netherlands. pp. 907-944.
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Comprehensive and current information on the culture of Sea Scallops in
Canada. Excellent references for further study of this topic.
Nova Scotia Ministry of Fisheries and Aquaculture – Species profile
(2006)
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Provides a detailed description of the hatchery and grow-out process for scallop
aquaculture.
Couturier, C., Dabinett, P. and Lanteigne, M., 1995. Scallop culture in Atlantic Canada.
In: A. Boghen (Ed.) Cold-water Aquaculture. The Tribune Press, Sackville, NB. pp.297-340.
Fisheries and Oceans Canada – Species profile (1995)
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Please note that while some of the industry information is a bit dated, this
profile provides an accurate and detailed description of the hatchery
and grow-out process for scallop aquaculture in Atlantic Canada.
Article: Scallop industry gets start with first spat collection in 1971
(produced in mid-late 1990s)
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Provides a historical account of scallop farming in Newfoundland and Labrador.
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