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The Atlantic cod (Gadus morhua) is one of 59 species of the family Gadidae. A marine fish which occurs mainly in cool waters in northern seas, the cod is soft-rayed, has three dorsal fins on its back and two anal fins behind its whitish-coloured belly, and generally has elongated hair-like projection called a barbel on its chin. It is generally grey or green but may be brown or reddish, depending upon the habitat into which its colour will generally blend. The scales are small and smooth. The mouth is large with a projecting upper jaw and the gill openings are wide. The lateral line of the cod is pale, and the tail is slightly concave, almost square. Generally cod average 2 to 3 kg in weight and about 60 to 70 cm in length. They usually do not exceed 30 kg, but there is one record of a cod that weighed about 96 kg and was more than 180 cm long.
In the Northwest Atlantic, Atlantic cod occur from inshore shallow water (about 5 m) to the edge of continental shelf, in water as deep as 600 m. They are distributed along the coast of east and west Greenland. The northern limit is off Frobisher Bay and extends into Ungava Bay. They become more abundant along the Labrador coast and off Newfoundland. They are distributed on the Flemish Cap, Grand Banks, Gulf of St. Lawrence, Nova Scotian Shelf, Gulf of Maine, and far south as Cap Hatteras. Cod in Canadian area are divided into stocks which are defined as recognizable units displaying characteristics unique to each stock with very little intermingling between adjacent stocks.
The cod in some of these stocks undergo extensive migrations. These migrations have been determined from the marking of cod with tags, which are later captured and tags returned by fishermen. Those cod which overwinter along the coast of southwest Newfoundland (4R + 4S + 3Pn) migrate and disperse into the northern Gulf of St. Lawrence, the Quebec North Shore and the Strait of Belle Isle during summer. In the Strait of Belle Isle north of Point riche in Newfoundland and Blanc Sablon in Quebec, the Gulf cod intermingle with schools of Labrador-east Newfoundland cod. Cod of the southern gulf of St. Lawrence (4t + 4Vn) overwinter off eastern Cape Breton and the continental shelf south of the Laurentian Channel and in summer return to the southern Gulf around Magdalen shallows, Chaleur Bay and Gaspé. There are local inshore populations of cod along the Nova Scotian coast which migrate only short distances. They remain mainly in the inshore area but move a short distance offshore to deeper water during winter and return inshore during summer.
Recaptures of cod tagged at inshore localities during the summer feeding migration suggest a strong degree of homing in subsequent years to the tagging area or areas immediately adjacent. Similar evidence for cod homing to their winter spawning ground also has been demonstrated. This homing tendency in cod is by no means as high as for Atlantic salmon, but is nevertheless significant in maintaining uniqueness to the characteristics of stock components.
The female Atlantic cod matures sexually at about six years of age, although the age at first maturity may vary from five to eight, depending on the spawning stock. The size at first maturity generally ranges from about 45 to 60 cm in length. The males generally mature at a slightly younger age and smaller size than the females. Cod spawning occurs over a wide area of the continental shelf and over a wide range of depth zones. Cod off Labrador and northern Newfoundland spawn from March to May along the outer slopes of continental shelf in depths from 200 to 600 m and bottom temperature of about 2.5° to 4°C. On the Grand Banks, spawning begins in April and continues to June. On the south coast of Newfoundland spawning begins in May. On the Nova Scotia banks, cod spawn in March and April. Occasionally in localized areas cod spawn during autumn.
Cod are very prolific. Female cod about 80 cm long produce about two million eggs, while a cod about 130 cm produced over 11 million eggs. The eggs are buoyant, round and about 1 to 2 mm in diameter. They float in water of about 30‰ salinity (coastal surface water). Thus they rise and remain at or near the surface while they hatching.
The fertilized eggs that rise to the surface and the resulting larvae are at the mercy of the currents and face immense hazards from larger predatory fish. The mortality rate is tremendous. Of the several million eggs each female spawns, only about one egg of each million succeeds in completing the cycle to become a mature cod. The newly-hatched larvae (about 5 mm long) depend for food on the yolk sac attached to the abdomen for about one to two weeks, after which the yolk is absorbed and the larvae must begin to forage for living food. At about a length of 4 cm, the young cod settle to the bottom and feed there or near the bottom.
Young cod fry feed mainly on copepods, amphipods and other small crustaceans in plankton. Juveniles feed mainly on shrimp, amphipods, euphausiids, and fush and shellfish larvae. Adult cod feed mainly on capelin, herring sand lance, flounders, young Greenland turbot, crabs, shrimp, brittle stars, comb jellies, and a host of other species of fish and shellfish.
Cod's age may be determined by counting the annual rings on the otoliths, two pearly-white earstones that form the balance mechanism in the cod's skull. Atlantic cod grow at different rates in different areas. There annual differences in growth rate in the same area depending upon population sizes, temperature, and food. Generally, growth is slower off Labrador and eastern Newfoundland then on the southern Grand Banks and is slower in the Gulf of St. Lawrence than on the Scotian Banks and Goerge Bank.
The inshore fishery traditionally has used a variety of gears such as cod traps, line trawl, longline, gillnet, handline, jigger, and in previous years, the cod seine. The offshore banks fishery by schooners traditionally used line trawls set out and hauled by men in dories on the coastal and offshore banks. Prior to 1900 the entire catch of cod was preserved by salting. In the twentieth century technological change heralded a new era into the fisheries for cod and other species. This was the introduction of the steam trawler and the otter trawl which had been developed in 1905 and which was itself based on the 1894 version of the beam trawl. This new fishing gear increased the catching efficiency of the fishing fleet.
In time, other new developments such as the stern trawler, more powerful winches, echosounders for fish detection, and automated floating fish factories to process and freeze the catches at the sea resulted in ever-increasing catches of cod and other species.
Catches of cod from the Northwest Atlantic were stable during the 1950s at about 900,000 t, but increased sharply during the 1960s to peak of almost 2,000,000 t, and declined dramatically during the 1970s to below 500,000 t in 1977. The European trawlers during the 1960s carried out a great winter and spring fishery on the prespawning, spawning and post-spawning concentrations of cod on the Southern Labrador and northern Newfoundland by reducing both quantities and sizes of cod. Eventually the stocks became overfished and there was a collapse of both inshore and offshore fisheries from their previous levels.
In 1973 the major cod stocks, and in 1974 all of the cod stocks in the Northwest Atlantic and in particular those of the Canadian area, were placed under a quota regulation. The Total Allowed Catch (TAC) for each stock was based upon scientific advice presented to the International Commission for the Northwest Atlantic Fisheries (ICNAF) which later became the Northwest Atlantic Fisheries Organization (NAFO). The stock division serves as a very useful management unit for management of the cod resources. There is 12 cod stocks in the in the Northwest Atlantic and two of those are in the Gulf of St. Lawrence :
1. Northern Gulf of St. Lawrence (NAFO divisions 4R+4S+3Pn)
2. Southern Gulf of St. Lawrence (NAFO divisions 4T+4Vn)
The TACs at first were not effective in curbing the overexploitation, mainly because enforcement was not effective and catches exceeded them in many cases. With the introduction of the 200-mile limit in 1977, the setting and enforcement of TACs in Canadian waters became a Canadian responsibility.
Adaptation of document: Atlantic Cod, by H. W. Lear, Coll. Underwater World, published by Communications Directorate, Department of Fisheries and Oceans, Ottawa, Ont. 8 p. 1984.