Geoscience Reference
In-Depth Information
The inshore cod fishery sustained coastal outports for half a millennium in Newfoundland.
Recent research has shown that cod courtship is a ritualized affair, not the random process it was once
thought to be. Male cod stake out the spawning grounds first and await arrival of the females to form spawning
columns, in which males and females ascend and descend together as if performing a courtship dance. Sound
may also play an important role in the spawning ritual. Male cod depress their pectoral fins, creating a sound
from their swim bladder: the bigger the fish and louder the sound, it appears, the more successful the male
suitor is. For whatever battery of reasons, larger females seem to prefer larger males and may even require
them for optimum breeding.
An average-sized female (80 centimeters, or 30 inches) will produce 2 million eggs (a large cod of about
130 centimeters, or 50 inches, could produce as many as 20 million). The round, buoyant eggs rise to the sur-
face, where they float until the little cod hatches after a period of days or weeks. The larva survives the first
week of life on its attached sac of yolk. Once the yolk sac is absorbed, the larval cod must also fend for itself
by finding small zooplankton or other fish larvae (icthyoplankton) while it is still at the mercy of the currents.
Not surprisingly, many perish at this vulnerable transition phase. By fall, the survivors, which may now have
drifted far from the spawning grounds, abandon the pelagic world and seek shelter on the seafloor, often in
coastal areas.
Rocky substrate or eelgrass beds provide cover from potential predators. In their second year, juveniles ven-
ture out to feed, becoming more vulnerable to predation from seabirds and from other fishes, including larger
cod. By the end of their second year, they leave their nursery areas and begin to form even-aged aggregations
known as shoals, which will be their habit throughout their lifetimes. By the third year they begin to follow the
great spawning and feeding migrations of their tribe and by six years old they enter the spawning population.
Although only one cod hatched from the million eggs spawned reaches reproductive age itself, it is enough to
sustain the population.
Opportunists that they are, cod have adapted to all available spawning habitats, offshore on the continental
shelf and in the bays of coastal waters. They have occupied all of the offshore banks, from northern Labrador
to the Grand Banks, to the banks of the Scotian Shelf and Georges Bank. Each stock shows a gradual adapta-
