Biology of Cod

The Atlantic Cod, Gadus morhua, is an omnivorous demersal fish species that inhabits both sides of the North Atlantic and can be found along the eastern coast of North America from Greenland to North Carolina. Cod may reach a weight of in excess of one hundred pounds, a length of over fifty inches and may live over twenty years; however an average fish caught today in the Gulf of Maine is three or four years old and will weigh five to ten pounds. The largest Atlantic Cod recorded from the Gulf of Maine was caught in 1969 and weighed 98 lbs 12 oz.[1] However, this cod is dwarfed compared to the 180-pound cod caught on Georges Bank in 1838 and the 211-pound cod caught off the coast of Massachusetts in May 1895.[2]

Adapting to the most readily available food source, cod consume practically everything in their path. Squid, herring and small crabs and lobsters are the staples of the cod diet, though they have been known to consume juveniles of their own species. A unique and defining characteristic of the cod is a long, slender organ protruding from its lower jaw known as a "barbell." This organ is thought to be used to detect prey that may be buried in the sand.[3]

Cod inhabit relatively shallow waters (100 feet or less) but migrate towards warmer, shallower waters to spawn during the winter and early spring.[4] Sexual maturity is attained between the ages of two and four, and at that age the female cod can produce a very large amount of eggs. Such a large number of eggs are released during spawning because only relatively few eggs will survive and develop into adults. As fish grow larger their ability to produce eggs grows exponentially.[5] A 40-inch female may lay about 3 million eggs and a 50-inch female up to 9 million eggs in one spawning season.[6]
It has been said that if each female cod in a lifetime of producing millions of eggs produces two juveniles that live to be sexually mature adults then the population would be stable.[7]
When the eggs are released they float to the surface. After a couple of weeks they hatch and the juveniles live out the next three weeks in the upper ocean avoiding herring and other small pelagics which feed vigorously on these fry. At this point they descend to the bottom and start their lives as demersals. If they are lucky and can avoid predators including adult cod, haddock, hake, flounder, other fish species and even green crabs[8], and reach a significant size, then they will have few enemies other than humans.

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