Gadus morhua
FAMILY
Gadidae
TAXONOMY
Gadus morhua Linnaeus, 1758, Atlantic Ocean and the coasts of Europe.
OTHER COMMON NAMES
None known.
PHYSICAL CHARACTERISTICS
Three separate dorsal fins, two separate anal fins. Dorsal and anal fins touching at their bases or separated by very narrow gaps. Chin barbel present. Pelvic fins sometimes with one elongate ray. Head relatively narrow and long. Snout to base of first dorsal fin length <33% of total length. Overall brownish to greenish gray on upper sides, paler ventrally. Body covered with spots, sometimes vague.
DISTRIBUTION
East coast of North America, north of Cape Hatteras, North Carolina, Hudson Bay, both coasts of southern Greenland, Iceland, coast of Europe from Bay of Biscay to Barents Sea.
HABITAT
Widely distributed in a variety of habitats from close to shore to depths >1,968 ft (600 m), but most common over continental shelf between 492 and 656 ft (150 and 200 m). Mostly demersal, although incursions into water column may coincide with feeding or reproduction. Also found in river mouths from late fall to early winter. Tolerates a wide range of temperatures and salinities, but larger fish generally occur in colder water 32–41°F (0–5°C).
BEHAVIOR
The Atlantic cod is a highly migratory fish. Patterns of migrations differ somewhat between regions. This pattern is associated with reproduction and seasonal temperature change in the Newfoundland stock (Rose 1993). Here, huge schools of cod leave their wintering areas in deep, oceanic waters, and follow tongues of deep, relatively warm, oceanic waters (or highways) across the continental shelf to summer feeding areas nearer to the coast. Spawning occurs in dense concentrations (>1 fish/m3) as they begin this mass movement, with multiple pairs of spawning fish observed in columns above the mass. As this huge mass migrates inshore, it periodically encounters important prey aggregations (such as capelin or shrimp) and disperses in order to feed. The mass is led by the largest fish (or scouts), and the smallest bring up the rear. After reaching nearshore waters, they turn and move northward along the Newfoundland coast in late summer, then eventually return to their deep-water wintering areas.
Off New England, Atlantic cod typically move into coastal waters during the fall, and then retreat into deeper waters during spring. A slightly different pattern occurs in the Great
South Channel area where they move southwesterly during the fall, spend the winter off southern New England and the Middle Atlantic coast, and then reverse this movement during the spring.
FEEDING ECOLOGY AND DIET
Diet changes with life history stage. The cod is generally omnivorous and voracious. For most ages, feeding occurs in twilight (dawn and dusk), but young fish feed almost continuously. Larvae feed on plankton; juveniles feed on invertebrates, especially small crustaceans; older fish feed on invertebrates and fishes, including young cod. Important diet items are likely to vary between study areas. Herring and capelin are important items in some areas.
REPRODUCTIVE BIOLOGY
Size and age at maturity have declined in recent years, most likely as a response to the fishery harvesting older and larger fish, or to a general decline in the stock biomass due to intense exploitation. A Scotian Shelf study (Beacham 1983) found that median age at maturity declined about 50% from 1959 (when age at 50% maturity was 5.4 years in males; 6.3 years in females) to 1979 (when age at 50% maturity was 2.8 years in both sexes). Median lengths at maturity declined from 20.1 to 15.4 in (51 to 39 cm) in males; 21.3 to 16.5 in (54 to 42 cm) in females. This smaller-and-younger-at-maturity trend continued between 1972 and 1995 in all zones between Georges Bank and Labrador, until presently in United States waters, maturity is reached between 1.7 and 2.3 years (median age) and 12.6 and 16.1 in (32 and 41 cm) (average length). Off the northeastern United States, the distribution of eggs indicates that important spawning occurs over the northeast peak of Georges Bank and around the perimeter of the Gulf of Maine. Reproduction peaks in winter and spring, but continues weakly throughout the year. The North Sea is a major center for reproduction in the eastern Atlantic, where spawning peaks between December and May. Eggs and larvae are pelagic, and juveniles begin descending to the bottom at sizes between 1.0 and 2.4 in (2.5 and 6.0 cm).
CONSERVATION STATUS
The Atlantic cod is listed as Vulnerable by the IUCN. Populations are heavily overexploited by fisheries and are at reduced levels of abundance. Both commercial landings and estimates of spawning stock size are at their lowest levels since 1960. Catch limits are strictly managed, and several important fishing grounds, e.g. portions of Georges Bank, have been closed to all fishing, largely in response to these low levels.
SIGNIFICANCE TO HUMANS
The importance of the Atlantic cod through history can hardly be overemphasized. For the past 1,000 years, the capture, preparation, and distribution of the cod has influenced the development of Western Civilization, especially around the perimeter of the North Atlantic Ocean. The Vikings crossed the Atlantic in pursuit of the cod. The Basques turned the cod into a commercial product in medieval times. Cape Cod was named in honor of the cod in 1602. The cod has actually been the cause of wars between countries, from American colonial times to recent conflicts between Iceland and Great Britain in the twentieth century. Newfoundland was settled by Irish and English natives in the early eighteenth century, largely because of opportunities in the cod fishery. Throughout most of the nineteenth century, this fishery was the most important source of employment and income for people in Newfoundland and much of Eastern Canada. In 1992, the cod population nearly reached a point of commercial extinction in waters off eastern Canada and Newfoundland, and a fishing moratorium was imposed. This moratorium has removed the main source of employment and income for thousands of fishermen from hundreds of small fishing communities and has truly devastated the Canadian economy.
