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The Cod, scientifically known as Gadus morhua, is groundfish that stays and obtains its food near the seafloor. It occurs in the northern hemisphere in large schools in moderate waters. The Atlantic Cod occurs throughout the colder and the deeper regions of the Northern Atlantic, starting from Greenland to North Carolina and Scandinavia. The larval Cod lives between the bottom and the substrate and can reach up to two meters in length.
The northwestern Atlantic Cod takes two years to mature, which is faster than its northeastern counterpart, which takes up to eight years to get reproductively ready. The Cod lives for about thirteen years, although some individuals have existed for two decades. Fishers catch the Cod using various methods, most predominantly gillnets, long lines, rods, and reels.
Although the adult Cod dwells in diverse habitats, it prefers rocky regions with unevenly distributed substrate. Adult Atlantic Cod feeds primarily on shellfish, young Haddock, mackerel, and capelin, while the small ones feed on shrimp, lobsters, euphausiids, spider crabs, and hermit crabs, among other crustaceans (Oceana, n.d.). The young Cod are eaten by the larger Cod and Pollock, while marine mammals and dogfish consume the adult Cod. Cod is edible; its translucent-while-raw meat has a mild flavor and turns white when cooked. For this reason, the species has a long, tumultuous aqua-culturing history.
Marine scientists and oceanographers always make observations and measurements on the oceans to know the behavior of organisms living there. If one adds warmth to water, it makes it lighter, and when adding salt, it will become denser. The seawater can be compressed slightly in large depths of oceans. The somewhat compressed seawater takes place in higher densities, and this brings the difference whereby the denser water is at the bottom while the lightest one is on the sea surface.
The water temperature is significant to the growth of the cod because it impacts the germination of some bacteria and phytoplankton that fishes eat. In the summer, the water surface becomes warm and colder during winter. Temperature change in seawater is caused by the mixture of water volumes with very different temperatures. The Canadian ocean’s water temperature ranges from 6 ºC to 20 ºC (Fisheries and Oceans Canada, 2019). For the Norwegian Atlantic, the water temperature during winter is below freezing point and has a habit of declining the weather as one approaches the east. In January and February, the temperature ranges from -6 ºC to -2 ºC from the east to the west (Aksnes et al., 2019). Ocean warming through increased stratification may result in decreased interior ocean ventilation.
Although the cod’s higher growth rates happen at higher water temperatures, slower paces of germination may not necessarily suggest reduced water temperatures (Wilson, 2016). Where temperatures are optimum, stock density may determine how fast and big the cod grows (Puvanendran et al., 2019).
If the density is low, the cod grows faster than if the density is high. Part of the reason is that excessive concentration of the fish in one area leads to competition for food, leading to stunted growth (Puvanendran et al., 2019). Yet, surprisingly, fish population build-up is initially due to the presence of adequate food. When a region has enough planktons, fish will have sufficient food and the right conditions for reproduction. Over time, their population will grow, and the food becomes scarce, which will push the fish population down again (Puvanendran et al., 2019). The repetitive cycle represents a self-regulating mechanism of sorts that helps maintain balance in the delicate aquatic ecosystem.
Variability in the cod’s growth rate may also be due to changes in the fish’s growth genes. For example, changes in these genes’ frequencies may inhibit or enhance the fish’s growth (Puvanendran et al., 2019). When trawlers remove big cod and leave small ones behind, they may inadvertently prevent the propagation of good growth genes (Renner-Martin et al., 2018). Subsequently, future fish generations may be smaller. Environmental conditions, including food availability and pollution, may also affect the fish’s genes and overall ability to grow fast and big (Renner-Martin et al., 2018). Thus, numerous factors influence fish growth, some of which may be difficult to identify.
Salinity is another factor impacting the growth and age of the cod. It refers to the amount of salt dissolved per a given volume of water. Almost all the elements in the periodic table are dissolved in the sea water, making them the saltiest (Hall, 2020). The cod is a salt water fish found only in the seas where the salinity is above one percent (Fisheries and Oceans Canada, 2019). The cod cannot survive or grow in fresh water where salinity is less than one percent (Fisheries and Oceans Canada, 2019).
In the Canadian Atlantic, salts serve as nutrients for phytoplankton, which later becomes fish food. The main ones include nitrites, nitrates, ammonium, phosphate, and silicate, representing 93% of dissolved compounds with a salinity rate of 35 parts per 1000 (Fisheries and Oceans Canada, 2019). In the Norwegian Atlantic, the main salt is Sodium chloride, and the salinity ranges from 30 to 40 parts per 1000 (Encyclopedia Britannica, n.d.). In both the Canadian Atlantic and the Norwegian Sea, saltiness increases with depth, which may explain why bigger cods are in the substrate.
In the Von Bertalanffy growth curve, male cods reach maturity slightly faster than females, and the longer the fish lives, the larger it is expected to grow (Aksnes et al., 2019). The phenomenon is caused by increasing growth and division of cells with time (Aksnes et al., 2019). When fish live longer, they may increase in mass significantly because of the increase in length over time (Aksnes et al., 2019). Therefore, male cods will be slightly heavier than females because they reach their maturity earlier and die younger (Aksnes et al., 2019). In some instances, there might be sex changes, for example, from male to female (Aksnes et al., 2019).
The Canadian and Norwegian larval Cod are reared on living zooplankton to examine size and temperature. Often, an increase in weight and length of larval and juvenile cods corresponds to increases in temperature from 4 ºC to 14 ºC, which also reduces the duration of the larval stage (Oomen et al., 2021). The larval size where the maximum growth occurs is between 0.1-1.0mg of dry weight, followed by a juvenile stage, both of which feed maximally at temperatures between 14 ºC to 16 ºC (Oomen et al., 2021). Favorable temperatures flourish phytoplankton, which serves as the Cod’s food (Oomen et al., 2021).
The growth rate of larval and juvenile Atlantic Cod is better in Norway as compared to Canada (Oomen et al., 2021). In the early juvenile stages, Norwegian variants of the cod tend to be heavier than the Canadian species (Renner-Martin et al., 2018). Norwegian Cod in larval and juvenile stages mature faster (takes two years) than the Canadian one (which can take up to eight years to grow) (Renner-Martin et al., 2018). These variations are due to differences in food availability in the two regions.
In the Norwegian Atlantic, fish mature faster because they have access to enough food. The warmer temperatures there promote plankton abundance leading to faster Cod maturation. Expectedly, the Norwegian Cod also dies earlier than the Canadian Cod. As shown in Figure 1, fish experiences rapid growth in the initial phase, followed by stagnant development in the final stage. Once the Cod reaches maturity size in terms of length and weight, it sizes to grow.
The growth rate of Cod in the Norwegian Atlantic is different from that of the Canadian Atlantic because the two regions experience different climates. The Norwegian Atlantic has high temperatures and warmer waters than the Canadian one. The Norwegian Atlantic phytoplankton receives more sunlight, thrives better, and gives the Cod more food. Not surprisingly, the Cod in the Norwegian Atlantic will grow faster than those of Canada. Norwegian’s Cod die earlier than Canadian because they grow and mature more quickly than those of Canada. The Canadian Cod are lighter than those of Norway, meaning they are exposed to displacement by sea waves and currents, meaning they are exposed to the dangers of predation. In return, this reduces their chances of growing to maturity.
Haddock and Pollock belong to the same family as the Cod and have many similarities. For instance, they are found at the seafloors and are popular food fish (Cod, Pollock, Haddock, Hake & Whiting, n.d.). However, there are some noticeable differences among them that help people tell them apart. The lateral line is light on cod and dark on Haddock (Albert, 2019). They also have different body colors, dorsal fin shapes, and body sizes and shapes. For example, while the Cod is green-brown with bigger and rounder bodies, Haddocks are dark-grey, smaller, slimmer, and pointier (Albert, 2019). All cod-like fishes continue to be important throughout the Atlantic for their economic contributions.
As per the von Bertalanffy growth curve, the growth rate of Pollock reduces with an increase in age. For instance, the length of Pollock decreases as it matures. The northwestern Atlantic Pollock reduces as ages go by almost the same but slightly higher than that of the northeast Atlantic Pollock (Cod, Pollock, Haddock, Hake & Whiting, n.d.). The northwest Atlantic seawater has a higher temperature than that of the northeastern. In return, this makes the phytoplankton grow higher on the Northwestern Atlantic compared to that of Northeastern Atlantic sea waters. It means that the Northwestern Atlantic Pollock will die faster or at an earlier age than the northeastern Atlantic Pollock. The Pollock’s initial growth is fast due to active cell division, and this curve flattens as the fish reaches maturity.
As per the von Bertalanffy growth curve, the growth rate of Haddock increases for some time before it declines significantly with the increase in age. It is an example of where the Haddock matures and grows older, and increases in length before it reduces in size. The Northwestern Atlantic grows almost at the same rate as that of the northeastern Atlantic before it decreases in length (Cod, Pollock, Haddock, Hake & Whiting, n.d.).
The only difference with the northeastern Atlantic is that the growth rate for Haddock is much higher than that of the northeastern Atlantic. In return, this means that the northwestern Atlantic Haddock tends to mature and grow older faster than that in the northeast Atlantic; hence they will die faster because the northwestern waters receive more sunlight, increasing the seawater’s temperature, which favors the phytoplankton’s growth rate. Moreover, at the beginning of the curve, the growth rate tends to rise for some period before it decreases. The reason is that when the Haddock are young, the body cells tend to be actively dividing for some time before they reach maturity, where they start reducing their body size.
Cod, Pollock, and Haddock’s growth curves per the von Bertalanffy growth curve differ in different regions. We will discuss the growth rates of Cod, Pollock, and Haddock as per the northwestern Atlantic. Here, all these species grow and mature faster than in the northeastern Atlantic. For Cod, the growth rate is much higher than those of Pollock and Haddock; it tends to maintain its length throughout its lifetime, i.e., at the age of six, it retains its length of 70cm (Cod, Pollock, Haddock, Hake & Whiting, n.d.).
Although there is overfishing, Cod still tends to be more abundant than the Pollock and haddock fish. One of the reasons is that the juvenile prefers eelgrass meadows as a beneficial habitat. It becomes advantageous since it increases their chances of survival due to their property of high density. Also, the availability of sunlight that increases the water temperature gives the Cod a better chance to produce many eggs. It is an advantage because there is less chance of Cod being exposed to extinction.
For the Pollock, the northwestern Atlantic subspecies growth curve, as per the von Bertalanffy growth curve, tends to decrease drastically with an increase in age. The size of Pollock reduces from 75cm to around 58cm in length (Cod, Pollock, Haddock, Hake & Whiting, n.d.).
Their chances of survival are not stable, and for that reason, they have large variations in their abundance concerning the few years they have to survive, i.e., twelve years. Another reason for such decline is that there are many other species; for instance, some marine mammals, seabirds, Steller sea lions, and fish eat Pollock, and their survival highly depends on the Pollock. For instance, during their spring migration, they move to the water surface to acquire food and breed. During winter, they move back to the deeper and warmer waters. All this exposes them to high chances of predation.
Regarding the von Bertalanffy growth curve, the growth rate for Haddock increases in the first years, i.e., 1970-1980, to reach the height of above 55cm and then drops slowly until 1990 where it maintains until 1995 where it keeps the length of 50cm after which drops until it reaches the size of 45cm (Cod, Pollock, Haddock, Hake & Whiting, n.d.). At first, the increase in length is due to the body cells of Haddock that are actively dividing. Also, at the beginning of the exploitation, the Haddock fish lays many eggs. In return, it gives them chances of survival at the beginning. The reduction in length over time is due to overfishing that leads to depletion of the Haddock. Their movement at different periods of the year places them at risk of being eaten by bigger fish and other aquatic animals.
When comparing the Canadian Cod and Norwegian Cod using the von Bertalanffy growth curve, the possible result is that the Norwegian Cod will grow and mature faster than the Canadian Cod. It means that the Norwegian Cod will increase in length with an increase in years faster than that of Canadian Cod. The growth will continue until it reaches its optimum size, where the body cells of these Cod will stop multiplying and maintain that length (Cod, Pollock, Haddock, Hake & Whiting, n.d.).
It implies that the Norwegian Cod will die faster than those of Canadians. This kind of growth is that in the Norwegian Atlantic, the sea waters receive more rays of sunlight, increasing the water temperature, i.e., the water temperature reduces as one approaches the east. In return, this will favor the growth of zooplankton on which the larval Cod will feed on and the growth of phytoplankton on which the juvenile Cod will live. In return, this will favor the Norwegian Cod’s growth compared to those of Canadians that receive less sunlight, hence low water temperature.
Therefore, the Norwegian Cod tend to reach maturity faster than those of the Canadian because they are heavier, probably because of the advantage of readily available food, for instance, the zooplankton and phytoplankton. During high tides and currents, they cannot be displaced. It is vital because they have fewer chances of being exposed to predation, and hence they can reach maturity faster without being disturbed. A bottom-dwelling fish, Haddock inhabit cool temperate waters ranging from the inshore areas to the continental shelf’s edge (Haddock, n.d.). Similarly, the Canadian Cod is lighter because of genetic variation (Albert, 2019).
Surprisingly, the Atlantic Cod, in general, has a broad diet; its juveniles feed on mysids and other crustaceans while adults predate on smaller fishes (Atlantic Cod, n.d.). During the high tide seasons, the eggs and the adult can be displaced, exposing them to predation. In most circumstances, there is higher fishing of Cod on the Canadian Atlantic than the Norwegian Atlantic. It disturbs their life cycle, whereby some fewer individuals reach maturity as compared to the Norwegian Cod.
Compared to the general growth rate of Cod to those of other species, for instance, the Pollock and Haddock using von Bertalanffy growth curve are always higher than the other species. One reason why the growth rate for Cod is higher than that of Haddock and Pollock is that it chooses the eelgrass habitat. This habitat is beneficial to the Cod because of the higher density, which increases their chances of survival.
Also, when there is sunlight, that increases the water temperature, which will accelerate the production of eggs by the Cod (Manabe et al., 2018). It is of significant value because there are many chances of survival, and the species cannot become extinct. For instance, other species, for instance, the Pollock, can be in search of food, mate, and search for a favorable temperature; they encounter many predators. The codfish is a bit heavier than that of other species, which helps them endure the water currents or high tidal levels on both sides of the North Atlantic Ocean (Atlantic Cod, n.d.). The filets of Cod are heavier and firmer than those of other species, like Haddock and Pollock.
Active fish protection is needed in the greater Atlantic region to preserve the fish diversity. Eradicating overfishing through protection will reduce the chances of extinction by protecting the larval Cod (Atlantic Cod, n.d.). The larger larval females should be protected in the refuge. Limits of catching fish should exist to discourage overfishing and Cod habitat destruction. One way to implement this is to enforce the minimum fishable cod size, which is currently 34 centimeters (Wilson, 2016). Restricting fishers to catching grown Cod only will allow juvenile and larval Cod to mature and reproduce. Another possibly effective cod protection initiative is helping cooperative anglers plan their fishing expeditions during the high season. Cooperative managers will ensure that members have appropriate fishing gear at all times.
The conservation statue of Cod helps to know whether the codfish is in existence and the future possibility of them becoming nonexistent. The females can produce approximately 2.5 million and 9 million eggs in one spawning based on the size (Oceana, n.d.). Atlantic cod reproduce in the winter and at early periods of spring by use of external fertilization. Spawning takes place at the seafloor, where the temperature ranges from 0 ºC to 12 ºC. Cod matures sexually at the age of 2 -4 years, although some may extend and spawn when seven years old (Puvanendran et al., 2019). Indeed, for years, one of the biological bottlenecks of the Atlantic cod culture’s commercialization has been early maturation.
Cod species are essential to Canada and Norway’s economies because the two countries export them to earn foreign income. Due to overfishing, predation, poor fishing methods, and global warming, the cod species are becoming very vulnerable. Other concerns include early maturation at 1-2 years before developing larger livers and reaching the preferred harvest weight of three kilograms (Puvanendran et al., 2019).
If governments do not allow fishers to catch cod indiscriminately, the species could become rare or go extinct. Other than overfishing, water pollution is also a risk factor in the cod’s extinction as polluted waters may directly kill the fish or poison their food (Puvanendran et al., 2019). The conservation of the cod requires concerted effort and more research to unveil what local communities need to do to protect these vital components of the global ecosystem.
The Canadian and Norwegian Cod belong to the same species and have a lot of similarities. The possible result of comparing them with a VB curve is that not much difference will show. However, males and females for the two subspecies will have different VB curves, with females being bigger. The curve will prove that the growth rate for both subspecies depends on species, size (age), sex (male or female), temperature, food, and genetic.
Since the Norwegian Atlantic has warmer temperatures, more plankton grows there, producing enough food for various fish species. As such, the VB curve will show that the Norwegian Cod is bigger than the Canadian one. Differences also exist between Cod and other species depending on their habitat. In this regard, northeast fisheries management needs to introduce regulations that help maintain warm temperatures for fish food to thrive, leading to a more significant fish population. Governments should base the Cod conservation effort on habitat protection. Access methods must not pollute the oceans or create microsystems that promote colder temperatures that affect fish food growth negatively.
References
Albert, N. (2019). Cod vs. Haddock: All You Need to Know. Fishing Booker. Web.
Aksnes, D. L., Aure, J., Johansen, P. O., Johnsen, G. H., & Salvanes, A. G. V. (2019). Multi-decadal warming of Atlantic water and associated decline of dissolved oxygen in a deep fjord. Estuarine, Coastal and Shelf Science, 228(2019), pp. 1-8. Web.
Atlantic Cod. (n.d.). Food from the Sea. Web.
Cod, Pollock, Haddock, Hake & Whiting. (n.d.). Clovegarden. Web.
Encyclopedia Britannica (n.d.). Norwegian Sea, North Atlantic Ocean. Web.
Fisheries and Oceans Canada (2019). Canada’s oceans now: Atlantic ecosystems, 2018. Web.
Haddock. (n.d.). Food from the Sea. Web.
Hall, D. (2020). Currents, waves, and tides. Web.
Manabe, A., Yamakawa, T., Ohnishi, S., Akamine, T., Narimatsu, Y., Tanaka, H., Funamoto, T., Ueda, Y., & Yamamoto, T. (2018). A novel growth function incorporating the effects of reproductive energy allocation. Plos One, 13(6), e0199346. Web.
Oceana. (n.d.). Ocean fishes: Atlantic cod. Web.
Oomen, R. A., Juliussen, E., Olsen, E. M., Knutsen, H., Jentoft, S., & Hutchings, J. A. (2021). Cryptic microgeographic variation in responses of larval Atlantic cod to warmer temperatures. Web.
Puvanendran, V., Lein, I., Bangera, R., Mortensen, A., & Thorsen, A. (2019). Family differences on triploid induction, sexual maturation and its contribution to sea cage performance of Atlantic cod, Gadus morhua. Aquaculture, 506, pp. 14-22. Web.
Renner-Martin, K., Brunner, N., Kühleitner, M., Nowak, W. G., & Scheicher, K. (2018). On the exponent in the Von Bertalanffy growth model. PeerJ, 6, pp. 1-25. Web.
Wilson, E. (2016). 10 ways world leaders can improve fishery management. Pew. Web.
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