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ysters are among the few ani- Where Found O mals that people of the world still eat American oysters range from the West THE AMERICAN alive and raw. They have a long history of Indies and the Gulf of north to the nourishing the human race. Gulf of St. Lawrence. They are found in OYSTER When the first white settlers arrived on greatest numbers in Chesapeake Bay and the shores of , one of the along the coast of the . Since most impressive indications they had of the Canadian waters are their northern richness of the new land was the abun- outpost, the Canadian percentage of the dance, large size, and excellence of the total North American harvest is very small. oysters. Friendly Indians reportedly In , oyster areas are restricted to brought oysters along with wild turkeys to the warm, shallow bays and estuaries of the the first Thanksgiving. They taught the set- southwestern Gulf of St. Lawrence and the tlers how to tong the bivalves with leather, coves of Cape Breton's Bras d'Or Lakes. and how to dry them for winter food. Water temperatures in other coastal areas On the eastern side of the , are generally too cold for their reproduc- oysters have been a prized food since the tion and suitable growth. They will tolerate pre-Christian era. The ancient Romans a temperature range of -2°C to 32°C (28°F served large quantities at their banquets, to 90°F). learned to cultivate them, and even made a They thrive best in areas where the monetary unit, the denarius, equal in value bottom is firm and non-shifting. Their to one oyster. preferred range of water salinity probably Oysters are animals that lack a lies between 2 and 2.7 per cent. Bays into backbone. They are scientifically classed as which rivers flow, and river estuaries into molluscs, a word from the Latin meaning which salty tides ebb and flow, meet their soft-bodied. Protecting their soft bodies are salinity requirement. However, water of the two hard shells or valves which are joined open sea, containing approximately 3 per by a hinge and held together by a strong cent salt, is too salty. muscle. is the leading Except in the earliest stage of their oyster-producing province followed by New development, oysters lack power of loco- Brunswick. The beds of Prince Edward motion. They are found lying motionless on Island's Malpeque Bay and Summerside the floor of brackish bays, coves and Harbour, combined with those of Caraquet estuaries, usually attached to rocks or other Bay in northern , account hard, submerged objects, sometimes in for about two-thirds of Canada's total east great clusters. coast oyster harvest. Other important Many different species of oysters occur in oyster growing areas include the bays and the inshore waters of the world's temperate inlets of the Bras d'Or Lakes, New and also tropical . The oyster native to Brunswick's Miramichi Bay, and Prince the North American Atlantic coast is Edward Island's Hillsborough and West Crassostrea virginica, commonly known as Rivers. the American oyster, the Atlantic oyster, and the Eastern oyster. It is a hardy species A well formed oyster shell indicates A Closeup able to live in waters with considerable Generally speaking, the shell of the uncrowded growing conditions and high variation in salinity and temperature. grade meat. American oyster is thick and has a rough, sculptured appearance. Its colour varies but is mainly a mixture of brown, gray, green, and white shades. The inside is a dull white and smooth to the touch. The two shells of the oyster differ in shape. The lower is cupped to accommodate the body, while the upper is flat and acts like a lid. Together they make an air and water-tight seal. A large adductor muscle, attached to both shells at a point slightly off centre, controls their opening and closing. While the power of the adductor muscle varies with the size and condition of the oyster, it takes a pull of over 9 kg (20 lb) suddenly applied, to open the shell of a 7.5

to 10 cm (3 to 4- inch) American oyster in good condition. Once opened, the muscle may be severed and the upper shell removed to reveal the soft, headless body of the oyster in the hollow of the lower shell. Underwater World 3

of the three, is muscular and mobile. It controls the flow of water in and out of the oyster. Under normal conditions, the outside of Oyster Populations the mantle adheres slightly to the shell. The • Medium Size parts of it not attached to underlying • Large Size organs enclose a large space known as the mantle cavity, which is normally filled with New Brunswick sea water. As the shell closes, surplus water is ejected and what remains keeps the or- gans constantly bathed. As long as the oys-

S ter keeps its shells closed and retains its shell Prince Edward Island liquor, it is able to stave off predators and also survive long periods of exposure to un- favourable water conditions and to air at 7• low tide. Other organs become visible when the ■ covering half of the mantle is removed. At the hinge end are the labial palps or lips surrounding the mouth; below are four porous, finely ridged, crescent-shaped gills, commonly called the beard. The gills function both as a respiratory and a food- collecting organ. Covering them are tiny, The body is made up of the organs of Principal oyster-producing areas of the lashing hairs which create an incoming Maritime Provinces. digestion, respiration and reproduction. current of water from which food particles Enveloping it is a sheet of tissue called the are filtered and oxygen absorbed. mantle, which is flat and featureless except Oysters breathe much like fish, using for its free borders which are thickened and both gills and mantle. The mantle is lined exhibit three parallel folds or ridges. Each with many small, thin-walled blood vessels ridge has a particular function. which extract oxygen from the water and The ridge nearest the shell margin expel carbon dioxide. A small, three- contains glands which secrete calcareous chambered heart, lying under the adductor material to build and repair the shell. In the muscle, pumps colorless blood, with its centre ridge are two rows of fine, dark supply of oxygen, to all parts of the body. tentacles or feelers which are extremely At the same time a pair of kidneys located sensitive. Any disturbing change in the on the underside of the muscle purify the water — mechanical, chemical, or related blood of any waste products it has Main features of the anatomy of the oyster to the amount of light, such as a passing collected. seen lying in its cupped shell with flat shadow — stimulates the nerves of the Incoming food is sorted by the lips and shell and covering half of the mantle mantle and causes the adductor muscle to accepted morsels pass down a narrow removed. close the shells. The inner ridge, the largest throat into a pouch-shaped stomach surrounded by a digestive gland. Waste passes through a long, coiled intestine to be emptied by the rectum into an exhalant chamber. There is no way of telling male oysters from females by examining their shells. While oysters have separate sexes, they may change sex one or more times during their life span. The gonads — organs responsible for producing both eggs and sperm — sur- round the digestive organs and are made up of sex cells, branching tubules and connective tissue. During the summer spawning period, the tubes are filled with eggs or sperm and at this time, the so-called spawn veins may be seen on the surface of the body. When spawning is completed, an oyster is almost translucent. Gradually the space which was occupied by the eggs or sperm becomes filled with animal starch, giving the body a smooth, creamy-white surface. Recondi- Underwater World 4

tioning or fattening, as this is called, takes When the water chills to around 4°C one-and-a-half to two-and-a-half months, (40°F), feeding ceases. The oysters stop depending on water and food conditions. filtering and seldom open their shells. How- ever, unlike hibernating bears and other Reproduction and Early Development animals which live on stored fat, they show The separate sexes of the American very little weight loss after the winter's oyster ripen in early summer. When the sleep. water warms to a triggering temperature of In the Maritimes, the American oyster's 20°C (68°F), they release eggs and sperm growth period is from May to late Novem- into the water. The spawn is not released all ber with a recess in July for spawning. It at once but at intervals over a period of takes a Gulf of St. Lawrence oyster from four to six weeks. During the spawning four to seven years to reach the legal market season, a single female, by clapping her length of 76 mm (3 inches) while oysters shells gently, will puff out many millions of grown in the warm waters of the Gulf of buoyant eggs and a male will release an even Mexico may take only two years to reach greater number of sperm. the same size. However, it is noteworthy Fertilization takes place in the open water that Canadian, slow-grown oysters tend to and cell division begins. The fertilized egg be of excellent quality. develops into a microscopic larva. Within Oyster growth continues throughout life, 24 hours it forms a shell and develops a but slows with age. Some oysters have swimming organ consisting of a disc attained a length of 38 cm (15 inches) and covered with vibrating hairs which can be have weighed over 1.35 kg (3 lb). Shell thrust out and withdrawn at will, allowing characteristics indicate that some found in free movement. the Bras d'Or lakes have lived for more For about three weeks, the little larva than 100 years. swims and drifts in the tidal currents and The shape and outer appearance of an may travel far from the spawning area. It oyster's shell reflect the conditions under Spat oysters after 5 month's growth on which it was grown. Crowding produces collector. feeds on microscopic plants of the plankton community of which it is a part. The shell distortions. On muddy bottoms and mortality rate is very high and only a small on overcrowded reefs, oysters assume a fraction of 1 percent of the young larvae vertical position and the shells grow long and narrow. On hard, clean bottoms, where reaches the next stage of development. there is no overcrowding, the shells grow When its length reaches about 300 round, strong, and are deeply cupped, pro- microns, or the size of a grain of pepper, ducing oysters of first-rate quality. each larva extends a probing foot and seeks a place of attachment. Once it finds a Enemies and Hazards suitable, clean, hard surface, the foot gland The Maritime oysters — both juvenile ejects a tiny pool of cement-like adhesive. and adult — are preyed upon by rock crabs Scallop shell collector covered with spat The little oyster then turns on its left side, and starfish, and are parasited by boring oysters about 1 week old and measuring cements itself to the object, and remains sponges and blister worms. The eggs and 1-2 mm. immobile for the rest of its life. Henceforth, larvae are also consumed by many of the it can feed only on what nutrients the water larger animals feeding on the plankton brings and is unable to escape overcrowding community. or flee from enemies. Adverse environmental conditions such The solid object of attachment is termed as freshets or sudden overflowings of cultch. The process of becoming cemented streams, prolonged exposure to freezing to the cultch is termed setting or spatting, temperatures at low tide, heavy silt or and the young oyster after setting, seed or marine plant growth (which can smother spat. Oyster larvae will attach themselves to oysters), as well as many types of industrial many types of cultch but seem to prefer and domestic pollution, all result in high mollusc shells and materials which contain oyster mortality. chalky substances. Micro-organisms may also prove to be Growth deadly enemies, such as the one causing Oysters grow by feeding on plankton — Malpeque disease, a serious infection which microscopic plants and animals present in devastated oyster stocks in Prince Edward the water. When water conditions are fa- Island between 1915 and 1940, and in New vorable, oysters feed almost continuously. Brunswick and Nova Scotia The warmer the water, the more active the between 1954 and 1957. Current oyster feeding, up to about 26°C (79°F). A 10-cm populations in the Maritimes, outside Cape

(4-inch) long oyster can filter or pump Breton, were spawned from oysters which water at a rate of about 9 to 13 L (2 to 3 gal) developed resistance to the disease through an hour. natural selection. Underwater World 5

In addition to life forms that prey on Farming oysters, there are those which compete with Oysters were likely the first sea animal to them for available space and food, causing be transported from one area to another a reduction in their numbers and impair- and cultivated as food. The ancient world, ment of their quality. Mussels, for example, while knowing little about the reproduction are their chief competitor in Maritime of oysters, knew much about the conditions waters. necessary for their growth. Pliny the Elder, a noted Roman naturalist of the first cen- The Fishery tury, has left an account of artificial oyster In the Maritimes, American oysters are beds established in Lake Lucrinus near harvested both from natural beds and from Naples by a Sergius Orata about 95 B.C. leased areas. Natural beds, not under lease, Orata's methods consisted of preparing are a common property resource and any- the grounds by removing other forms of one who purchases a licence is allowed to marine life, planting seed oysters, culti- fish them. It has been estimated that there is vating the oysters by keeping them separat- a total of 6 200 hectares (15 500 acres) of ed in order to grow to a well-formed, good oyster bottom in the Maritimes, of mature size, and finally harvesting them which 624 hectares (1 560 acres) are natural when they were ready for market. beds open for public fishing, 3 700 hectares Modern oyster farming, based on the (9 250 acres) are privately leased areas, and knowledge of oyster biology, basically 1 876 hectares (4 690 acres) are unused. follows the Roman procedure. It began in in the 1930s and has since In Canada, the Department of Fisheries been encouraged by the federal Department and manages and regulates Ameri- of Fisheries and Oceans which leases can oyster harvesting. A rather complicated growing areas. set of regulations governs oyster fishing Leased areas consist of subtidal land, seasons. Seasons differ for public and devoid of natural beds, yet considered suit- leased ground but, in effect, oysters are able for oyster culture. They vary in size fished from August 15 to May 1, the from 0.4 hectares to 40 hectares (1 to 100 principal harvest being taken in autumn. acres). The lessee has property rights over Harvesting methods include the use of the oysters on his lease and is required to rakes, tongs and dredges. Handpicking is cultivate the lease as a commercial venture Tonging oysters. also practised at low tide in shallow waters. under penalty of forfeiture if planting and Raking is done by hand on sloping bot- production requirements are not met. toms reaching depths up to 7.6 m (25 ft). The rakes have long handles and long, Up to one-half of the Canadian Atlantic slightly curved teeth. Sometimes a shallow oyster crop currently marketed is raised for bag of wire netting is attached to the back some period of time on the leases and this of the head. percentage is expected to increase. Tongs are also hand operated. They To start a farm, the lessee may catch seed consist of two long-handled rakes hinged oysters on cultch placed in certain reserve about one-third of the distance up from the areas of the public grounds. He may pur- Oyster drag or dredge. heads and may have a basket of wire netting chase seed oysters from a supplier, if one on the back of one or both heads. They are can be found. Or, he may obtain a permit used on level bottoms in depths up to 5.4 m from the federal government entitling him to gather wild oysters from the public (18 ft). The dredge, also called the drag, can be grounds and contaminated areas for relay used to fish for oysters at greater depths. It to his lease. Oysters from contaminated was developed to reduce costs in large-scale areas, relayed to clean water, cleanse harvesting operations and might be likened themselves in a few months and are then to a large rake-head backed with a bag and safe for human consumption. attached to a strong rope in place of a Up to now, most of the lessees have handle. It is towed over the bottom by a chosen the third alternative. However, powered boat and hoisted either by hand or increasing numbers are electing to collect by a mechanical or motor-driven device. their own seed oysters and rear them to For conservation reasons, rakes and tongs market size. are the only gear permitted on public A major problem in the Maritimes is a grounds. shortage of natural seed stock.Regrettably, After harvesting, oysters are culled. due to the low water temperatures in some Undersized oysters and old shells are areas, setting of oyster larvae in commer- returned to the beds. Predators such as cially significant quantities does not occur starfish and rock crabs, taken incidentally, every year. are destroyed. Cleaning, grading, packing To help solve the problem, the federal and shipping complete the operation. fisheries department set up an experimental Underwater World 6

oyster hatchery at Ellerslie, Prince Edward Further Reading: Island, in 1965. It was charged with devel- Galtsoff, P.S. oping reliable techniques for seed oyster 1965. The American Oyster Crassos- production, assessing their commercial trea virginica Gmelin. U.S. Fish and aygial Zft Allatitior value, and encouraging development of Wildlife Service, Fish. Bull. vol. 64: private commercial hatcheries in the Mari- 480 p. times. Although this hatchery demon- Medcof, J. C . strated that oysters can be artificially 1961. Oyster Farming in the Mari- spawned and reared successfully, the pro- times. Fish Res. Board Can. Bull. 131: cess proved too costly to be commercially 158 p. viable. Morse, N.H. Off-bottom culture of oysters making use 1971. An Economic Study of the of rafts, floating longlines, and fences, has Oyster Fishery of the Maritime Pro- become popular in certain areas of the vinces. Fish. Res. Board Can. Bull. Maritimes, especially the Bras d'Or Lakes 175: 81 p. area. Instead of spreading the cultch over a Various authors. bottom area, growers string it like beads on 1979. Oyster Leasing Policy in the wire or nylon rope, then suspend it above Maritime , Resource Branch of the bottom at the appropriate time to col- Dept. Fisheries and Oceans, Halifax, lect the setting larvae. The collected spat are N.S. 13 p. grown in suspension until they attain the Various authors. desired length, after which they are separat- 1975. The Proceedings of the Bras ed from the cultch and either planted on the d'Or Lakes Aquaculture Conference, bottom or placed on trays suspended in the College of Cape Breton Press p. water to strengthen and repair their shells. 119-150 incl. Held in suspension, oysters grow more Oyster rafts moored in series. rapidly than on the bottom because better Text: K.D. Stewart water circulation increases the availability Communications Branch of food. However, as a result of rapid Fisheries and Oceans growth, their shells tend to be thin. In order Ottawa, to produce shell qualities of the shape and K1A 0E6 thickness desired by Canadian consumers, Underwater World factsheets are brief the oysters need to be held for an additional illustrated accounts of fisheries resources year or two on the bottom or on suspended and marine phenomena prepared for public trays. information and education. They describe the life history, geographic distribution, utilization and population status of fish, Off to Market Canada's somewhat low production of shellfish and other living marine resources, American oysters — a little over 1 361 t and /or the nature, origin and impact of Loading oyster rafts with T-bars threaded marine processes and phenomena. (3 million lbs) a year, in-shell weight — has with strings of scallop shell spat Others in this series: collectors. resulted in the entire catch being marketed in the shell. As the demand for them Atlantic Shellfish exceeds the supply, their price is relatively Atlantic "Pelagic" Fish high, although it differs with the grade. The Atlantic Groundfish grade system classifies these oysters as Capelin Irish Moss Fancy, Choice, Standard, and Commercial, Red Hake depending on shape standards which are Red Tides based on the relationship between their Roundnose Grenadier length and width. For the most part, Canadian Atlantic The Atlantic Snow Crab oysters are harvested in the fall. They are The Sea Scallop capable of living out of water for about Published by: four months, providing the temperature is Communications Branch maintained just above freezing and the Department of Fisheries and Oceans atmosphere is damp. Packed in large Ottawa, Ontario wooden or cardboard boxes, they are K1A 0E6 shipped primarily to cold storage facilities in and City from where UW 82/014E they are sold to retail stores, hotels, © Minister of Supply and Services Canada 1982 and large, organization-sponsored "oyster Cat. No. Fs 41-33/14-1982E parties," Few, if any, are shipped west of ISBN 0-662-12132-5 and only an insignificant quantity is exported. Disponible en francais