Alaska pollack
| Alaska pollock | |
|---|---|
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Gadiformes |
| Family: | Gadidae |
| Genus: | Gadus |
| Species: | G. chalcogrammus |
| Binomial name | |
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Gadus chalcogrammus Pallas, 1814 |
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| Synonyms | |
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Theragra chalcogramma (Pallas, 1814) |
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Theragra chalcogramma (Pallas, 1814)
The Alaska pollock or walleye pollock (Gadus chalcogrammus) is a marine fish species of the cod family Gadidae. It is a semipelagic schooling fish widely distributed in the North Pacific with largest concentrations found in the eastern Bering Sea.
While belonging to the same family as the Atlantic pollock, the Alaska pollock is not a member of the same Pollachius genus. Alaska pollock was long put in its own genus Theragra and classified Theragra chalcogramma, but more recent research has shown it is rather closely related to the Atlantic cod and should be moved back to genus Gadus in which it was originally described. Furthermore, Norwegian pollock (Theragra finnmarchica), a rare fish of Norwegian waters, is likely the same species as the Alaska pollock.
The speckled colouring of Alaska pollock makes it more difficult for predators to see them when they are near sandy ocean floors. They are a relatively fast-growing and short-lived species, currently representing a major biological component of the Bering Sea ecosystem. It has been found that catches of Alaska pollock go up three years after stormy summers. The storms stir up nutrients, and this results in phytoplankton being plentiful for longer, which in turn allows more pollock hatchlings to survive. The Alaska pollock has well-developed drumming muscles that the fish use to produce sounds during courtship, like many other gadids.
The primary factor in determining the foraging behavior of the Alaskan pollock is age. Young pollocks can be divided into two sub-groups, with lengths below or above 60 mm. Both groups mainly feed on copepods. A limited supply of copepods may lead to food depletion. However, the larger group is also capable of foraging for euphausiids and is able to diversify its food sources. Therefore, food depletion has a larger effect on smaller pollocks.
The variation in size of each subgroup also affects seasonal foraging behavior. During the winter, when food is scarce, foraging can be costly due to the fact that longer hunting time increases the risk of meeting a predator. The larger young pollocks have no need to hunt during the wintertime because they have a higher capacity for energy storage while smaller individuals do not and, therefore, have to continue foraging thereby putting themselves at greater risk. To maximize their chances of survival, the larger group increases their calorie intake to gain weight in autumn, while the smaller group focuses solely on growing in size.
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Wikipedia