Walleye pollock
The Alaska pollock or walleye pollock (Gadus chalcogrammus) is a marine fish species of the cod genus Gadus and family Gadidae.
It is a semi-pelagic schooling fish widely distributed in the North Pacific, with largest concentrations found in the eastern Bering Sea.
Alaska pollock was long put in its own genus, Theragra, and classified as Theragra chalcogramma, but research in 2008 has shown it is rather closely related to the Atlantic cod and should therefore be moved back to Gadus, where it was originally placed. In 2014, the U.S. Food and Drug Administration announced that the official scientific name for the fish was changed from Theragra chalcogramma back to its original taxon Gadus chalcogrammus, highlighting its close genetic relationship to the other species of the cod genus Gadus. Since 2014, registries of scientific names for fish species (e.g. the United Nations’ ASFIS list and the World Registry of Marine Species (WoRMS) have largely adopted the Gadus chalcogrammus name.
The change of the official scientific name was followed by a discussion to change the common name as well, to highlight the fish as a member of the cod genus. The common names "Alaska pollock" and "walleye pollock", both used as trade names internationally, are considered misleading by scientific and trade experts, as the names do not reflect the scientific classification. While belonging to the same family as the Atlantic pollock, the Alaska pollock is not a member of the genus Pollachius, but of the cod genus Gadus. Nevertheless, alternative trade names highlighting its placement in the cod genus, such as "snow cod", "bigeye cod", or direct deductions from the scientific names such as "copperline cod" (gadus meaning 'cod', Latin: chalco- from Greek: khalkós meaning 'copper', and Greek: grammí meaning 'line') or "lesser cod" (from the synonymous taxon Gadus minor) have yet to find widespread acceptance. The National Oceanic and Atmospheric Administration even states that " might never change, as common names are separate from scientific names".
In addition, Norwegian pollock (Theragra finnmarchica), a rare fish of Norwegian waters, is likely the same species as the Alaska pollock.
The speckled coloring 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, fish with lengths below.mw-parser-output.frac{white-space:nowrap}.mw-parser-output.frac.num,.mw-parser-output.frac.den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output.frac.den{vertical-align:sub}.mw-parser-output.sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}60 mm (2+1⁄2 in) and fish greater than 60 mm. Both groups mainly feed on copepods. However, the latter group will also forage for krill. Therefore, food depletion has a larger effect on smaller pollock.
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 winter because they have a higher capacity for energy storage, while smaller fish do not, and have to continue foraging, putting them at greater risk. To maximize their chances of survival, large pollock increase their calorie intake in autumn to gain weight, while smaller ones focus solely on growing in size.
Alaskan pollock exhibit diel vertical migration, following the seasonal movement of their food. Although pollocks exhibit vertical movement during the day, their average depth changes with the seasons. Originally, the change in depth was attributed to the amount of light or water temperature, but in fact, it follows the movement of food species. In August, when food is abundantly available near the surface, pollocks will be found at shallower depths. In November, they are found deeper along with their planktonic food source.
