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.
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