Atlantic cod are marine benthopelagic fish, living near the bottom and in the open ocean (Riede 2004). Cod also inhabit brackish waters. Cod can be found in a wide range of habitats within the ocean, from the shoreline down to the continental shelf. They can be found at depths of 500 to 600 meters in coastal waters and are also numerous in open ocean waters. These fish are located in a temperate climate with a range in temperature from 0 to 20 degrees Celsius. Geographically the majority of the population lies within a latitude of 80 to 35 degrees north (Frimodt 1995). (Riede, 2004; Wildscreen, U.K. Charity, 2004)
Atlantic cod reach a maximum length of 150 to 200 cm. On average, cod weigh 40 kg and the greatest recorded weight is 96 kg. The color of Atlantic cod varies with respect to the enviroment in which the fish lives. Water with large volumes of algae will yield a red to greenish skin color. A pale grey color is more prevalent for fish found on the ocean floor or on sandy bottoms. The Atlantic cod has 1 chin barbel, 3 dorsal fins, and 2 anal fins. It also has a pronounced lateral line from the gills to the tail (Wildscreen and U.K. Charity 2004). The coloring of cod is often shaded from top to bottom. The dorsal area of the fish may be a rich brown to green and fade to silver towards the ventral side. Some cod may have brown/red spots on the sides and back. ("Wikipedia: Encyclopedia", 2005; Wildscreen, U.K. Charity, 2004)
Atlantic cod pass through a series of four life history stages as they develop. Initially they begin as pelagic eggs which are located in harbors, bays, and offshore banks. The eggs are associated with an incubation temperature around 2 to 8.5 degrees Celsius. The eggs are buoyant and remain close to the surface waters. Studies have shown that egg mortality is independent of temperature but increases at lower salinities. Next, the larval stage takes place. Larvae are located in pelagic waters and their growth is correlated with the volume of zooplankton which can feed upon the sac larvae at this stage. During the third stage, juveniles occur in coastal and offshore waters in the summer and deeper waters in the winter. They are tolerant of temperature changes from 6 to 20 degrees Celsius and they often use vegetation as a predator avoidance strategy. The final stage is adulthood. They live at temperatures less than 10 degrees Celsius and primarily inhabit the ocean floor. (Fahay, et al., 1999)
There is a limited amount of information on Atlantic cod spawning behavior which may suggest complex mating systems. Researchers are aware that mating behavior in Atlantic cod can include reproductive strategies such as sound production by males and mate selection by females. Although these behaviors have been observed, the causes and consequences of such behavior, and their specific interplay within the mating systems continue to be studied. Atlantic cod are considered "batch-spawners", as females only release 5 to 25% of their total egg complement at any time. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; Rowe and Hutchings, 2004)
One study on the acoustic sound production of Atlantic cod provides some insight into possible mating behaviors. Drumming muscles are present in both males and females, yet males tend to have more pronounced muscles. The mass of the drumming muscles increases in males prior to spawning and larger males have larger muscles. This suggests that the amplitude of sound production might be a determinant in the success of spawning and selection by females. Observations of Atlantic cod behavior support the hypothesis that females are responsible for mate selection. The biology of the drumming muscles in males, as well as the circling behavior of numerous males around prospective females supports the female selection hypothesis. It is worth noting that dominance hierarchies can also be established. Males with greater body sizes and those who were successful in spawning sometimes appear to dominate the population and act aggressively towards “lesser” males. (Rowe and Hutchings, 2004)
Recent research suggests that anthropogenic noise pollution in the water (via oil/gas exploration and drilling) could pose a threat to the success of sound production and the role it plays in the reproduction process. (Rowe and Hutchings, 2004)
Many stocks of cod exhibit migratory behavior during their reproduction season due to seasonal variations in water temperature. Typically, a cod population moves into warmer waters during winter and early spring to begin spawning. Although spawning can occur year round, peak spawning levels occur in the winter and spring. As the population moves inshore it may disperse temporarily to feed if large amounts of prey are present. Cod spawn annually, and spawning takes place within a three month period. Cod employ a ventral mount position in which a male uses his pelvic fins to clasp onto a female and then position himself properly beneath her. Cod spawn in dense concentrations of more than 1 fish per cubic meter and multiple pairs of fish can be observed spawning in the same water column. Spawning occurs near the ocean bottom in temperatures between 5 to 7 degrees Celsius. The eggs that are produced are pelagic, and drift (often towards the surface) for approximately 2 to 3 weeks before hatching and reaching the larval stage. There is some debate as to the age of sexual maturity for cod. Age and size at maturity often vary amongst different populations with northeastern populations maturing around 5 to 7 years and southern populations maturing between 2 to 3 years. A recent finding suggests that cod are moving towards a reduction in age and size for sexually mature fish. In 1959 the median age of maturity was 6.3 years for females and 5.4 years for males. In 1979 the age of maturity was listed as 2.8 years for both sexes. Now, the median age of sexual maturity is between 1.7 to 2.3 years and corresponds to a length of 32 to 41 cm. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; Fahay, et al., 1999; Rowe and Hutchings, 2004)
There is no indication that any parental involvement exists on the behalf of either females or males after the eggs are released. The high mortality rate of the offspring (eggs) is attributed, in part, to the lack of parental care. The reproductive strategy of high fecundity levels may be a response to the absence of protection the eggs receive once released into the water. Although the survival rate is low, the sheer number of eggs produced is huge. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003)
Atlantic cod can reach a maximum lifespan in excess of 20 years, with a minimum lifespan of a few hours/days (shortly after the eggs are released). Within the last 100 years typical lifespans have changed drastically as a result of commercial cod fisheries. Most recently, fisheries have begun harvesting younger fish. (Wildscreen, U.K. Charity, 2004)
Seasonal migrations of Atlantic cod are attributed to water temperature, food supply, and spawning grounds. Atlantic cod move as a group and tend to follow warmer water currents during these times. Although they prefer a habitat in which water temperature ranges from 2 to 11 degrees Celsius, some populations have been found as low as -1.5 degrees Celsius. Cod are able to withstand such cold temperatures by producing plasma antifreeze proteins which prevents their blood from forming ice crystals. Certain populations seem to have leaders (the largest size class) which guide the mass of fish through the migration route. It is also speculated that the youngest fish actually learn the migration path from the older fish. Changes in fish stocks (e.g. reduction of older fish) might result in different migration paths being created.
Dominance hierarchies created by spawning males may result from differences in body size and aggressive interactions. Larger fish are often observed playing a dominate role over smaller fish. Those with a higher rank in the hierarchy are more likely to defend their territory. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; Fahay, et al., 1999)
No information clearly defining the home range of Atlantic cod could be found.
There is limited information available on the communication among cod. Atlantic cod are hypothesized to communicate through the production of sound via drumming muscles. Sound production is correlated with mate selection during spawning season. It is hypothesized that the degree to which males are able to produce acoustic sound is positively associated with the overall fitness of the males, with those having larger drumming muscles producing greater sound waves and out-competing others. (Rowe and Hutchings, 2004)
The diet of Atlantic cod is best described as opportunistic because they feed on anything they are capable of capturing. At all life stages, however, they eat primarily other animals. During the larval stage they feed on smaller organisms such as zooplankton. Juveniles feed on shrimp and other small crustaceans. Adult Atlantic cod consume squid, mussels, clams, tunicates, comb jellies, brittle stars, sand dollars, sea cucumbers, and polychaetes, and are also cannibalistic. The choice of prey included in the diet seems to play a role in determining the skin color of cod. Those that feed on crustaceans tend to appear more brownish in color whereas a blue-green pigment may be the result of a diet consisting primarily of fish. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; Riede, 2004)
Atlantic cod populations respond differently to predators depending on what region of the Atlantic Ocean they occupy. Atlantic cod are susceptible to being consumed by large marine mammals (harp and harbor seals) and sharks. In the northwest Atlantic Ocean most of the large predatory fish have been removed and cod (and similar species) act as dominant predators in this region. In other parts of the Atlantic Ocean with large harp seal populations the number of Atlantic cod has been greatly reduced due to consumption by seals. Cod larvae are vulnerable to smaller predators such as zooplankton. Juveniles are preyed on by species such as dogfish, squid, and halibut. Cannibalistic behavior becomes apparent as adult Atlantic cod readily consume juveniles. Although adult Atlantic cod have relatively few predators compared to their young, they still must be on the lookout for large marine animals. The greatest predatory threats to cod are those that lurk above the surface. Humans are responsible for drastically lowering Atlantic cod populations through well-developed fisheries. The economy of several regions is dependent upon these fisheries and the great demand for large numbers of Atlantic cod has resulted in overfishing and reduced cod stocks. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; "Wikipedia: Encyclopedia", 2005; Riede, 2004)
The main role that Atlantic cod have in the ecosystem is their involvement in the food chain. Atlantic cod feed upon a variety of organisms such as invertebrates, crustaceans, and zooplankton. Larger marine organisms (i.e. sharks, seals) prey upon and consume Atlantic cod. The interplay between predators and prey is the key way in which cod influence their ecosystem. No information concerning specific relationships (mutualism, parasitism, etc.) was available. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; Campbell, 2005)
Atlantic cod provide an extremely important fishery in many regions especially in the northwest Atlantic. The success of this commercial fishery has been the main source of economic wealth for areas such as New England and Canada, with Atlantic cod even being labeled “Newfoundland currency”. Up until the 1990’s, Atlantic cod was not only an economic mainstay for many people but also a dominant member of the food chain within the waters of the Atlantic. Atlantic cod is marketed widely, primarily for human consumption. The flesh is mild and Atlantic cod are a popular table fish. The liver of Atlantic cod is also processed to produce cod liver oil which is used as a vitamin supplement. ("Assessment and Update Report on Gadus Morhua (Atlantic Cod)", 2003; Campbell, 2005; Riede, 2004)
Although Atlantic cod have been an economic asset to humans, they can also create problems for economies based solely on cod fisheries. Those who depend upon the success of cod fisheries as a source of income can be hurt financially if fisheries fail. The collapse of the cod fisheries in the 1990’s took a toll on the economies of New England and Canada. In this case, the stocks were not managed properly and resulted in a 96% decrease in population size since 1850. Fishermen who rely on the cod population to make a living are left with financial burdens when the stock collapses. (Campbell, 2005)
Atlantic cod was listed as a vulnerable species in 1996. In the early 1990’s many cod populations collapsed in areas where commercial fishing was intense. The collapse is attributed to overfishing, and specifically to the commercial fishing of older/larger cod which resulted in a smaller population of fertile females and the harvesting of young fish before they have had a chance to mature and reproduce. The prosperity that fishermen enjoyed prior to the collapse lured many into the commercial fisheries and as a result the cod population was negatively affected.
Some efforts have been made to help certain cod populations rebound. Moratoriums and fishing regulations were placed in regions of Canada but were unsuccessful in maintaining or increasing population size. The main deterrent in properly managing cod stocks relates to the geographic range which the cod occupy. Cod are found throughout the waters of the Atlantic, and since these are international waters it makes it difficult for any one region to impose certain regulations. Research shows that populations can easily fall below the “Safe Biological Limits,” which represent the number of fish needed to maintain a proper population. Biologists argue that regulation alone will not be enough to keep the cod population at a sustainable level, but it is a start. Suggestions such as no-catch zones in areas of spawning and along migration routes may be helpful if enacted. As cod stocks move towards critically low levels, it is apparent that serious conservation efforts must be put into place to prevent the devastation of this important fish species. (Campbell, 2005; Wildscreen, U.K. Charity, 2004)
Tanya Dewey (editor), Animal Diversity Web.
Courtney Wilmot (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
uses sound to communicate
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
an animal that mainly eats fish
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
mainly lives in oceans, seas, or other bodies of salt water.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
breeding takes place throughout the year
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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Fahay, M., P. Berrien, D. Johnson, W. Morse. 1999. Atlantic Cod (Gadus Morhua) Life History and Habitat Characteristics. National Ocean and Atomospheric Administration Technical Memorandum, 122-152: 1-35. Accessed October 13, 2005 at http://www.nefsc.noaa.gov/nefsc/publications/tm/tm124/tm124.pdf.
Frimodt, C. 1995. Fishing News Books: Multilingual illustrated guide to the world's commercial coldwater fish. Oxford, England: Osney Mead. Accessed October 13, 2005 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=69.
Luna, S., E. Agbayani. 2005. "Species Summary" (On-line). Accessed October 11, 2005 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=69.
Riede, K. 2004. Global register of migratory species - from global to regional scales. Final Report of the R&D-Projekt:Federal Agency for Nature Conservation, 808 05 081: 329. Accessed October 13, 2005 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=69.
Rowe, S., J. Hutchings. 2004. The function of sound production by Atlantic Cod as inferred from patterns in variation of drumming muscle mass. Canadian Journal of Zoology, 82: 1391-1398. Accessed October 17, 2005 at http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?_handler_=HandleInitialGet&journal=cjz&volume=82&calyLang=eng&articleFile=z04-119.pdf.
Wildscreen, U.K. Charity, 2004. "ArKive: Gadus Morhua" (On-line). Accessed October 11, 2005 at http://www.arkive.org/species/ARK/fish/Gadus_morhua/more_info.html.