This species is not threatened and is not listed on the 2004 IUCN Red List of Threatened Species nor is it listed as endangered by the U.S. Fish and Wildlife Service. The most important site of reproduction for this species, the Shelikof Strait in the Gulf of Alaska, has an annual period of time in which fishing is prohibited. This enforced fishing restriction was put in place to prevent potential decreases in this species due to this region having such a large T. chalcogramma density during spawning season (Bailey 1999).
US Federal List: no special status
CITES: no special status
Limited information pertaining to the communication and perception of Theragra chalcogramma exists. Most schooling fish, however, use visual cues for schooling and feeding (Bailey 1999).
Communication Channels: visual
Perception Channels: visual ; tactile ; chemical
Theragra chalcogramma larvae are preyed on by northern rockfish, polka-dot snailfish, and atka mackeral. One-year-olds are preyed on by greenland turbot, plain sculpin, and arrowtooth flounder. Those that are two years old are hunted by greenland turbot, bigmouth sculpin, sablefish, pacific cod, plain sculpin, pacific halibut, and great sculpin. Adult T. chalcogramma fall prey to yellow irish lords and plain sculpin (Cohen 1990; Kooka 1998). In the Gulf of Alaska, T. chalcogramma is the primary prey of stellar sea lions (Cohen 1999).
Known Predators:
Theragra chalcogramma has an olive-green belly. Its dorsal side displays a gradually darkening color scheme from the bottom to the top, eventually fading to a dark brown. This fish exhibits characteristic blotches all over its entire body, which is slender with a large head. The head consists of various lateral pores, large eyes, and a protruding lower jaw which lacks a barbel (Bailey 1999). Theragra chalcogramma can be recognized by its two anal fins, three widely dispersed fins on its back, and outstretched pelvic fins. The fins are all a dark grey to black color. A lateral line runs across the fish to its caudal fin. At three to five years old, the average length of this fish is 30.5 centimeters (Harmann 2005). By the time it reaches ages of eight to twelve years, the average length is about 61 centimeters. The maximum length of T. chalcogramma is 91 centimeters. Weights of this fish range from 600 grams to 800. The maximum weight was recorded at 1400 grams (Cohen 1990).
Range mass: 600 to 800 g.
Range length: 30.5 to 91 cm.
Average length: 61 cm.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
The mortality coefficient for Theragra chalcogramma is 0.3 on the eastern Bering Sea shelf (0.3 implying that that the annual natural morality rate is 30%) and 0.2 on the Aleutian Basin. Theragra chalcogramma usually lives from 12 to 16 years. The oldest T. chalcogramma ever reported was 31 years old (Bailey 1999).
Range lifespan
Status: wild: 31 (high) years.
Typical lifespan
Status: wild: 12 to 16 years.
Average lifespan
Status: captivity: 17 years.
Theragra chalcogramma is a saltwater fish that thrives in seas, oceans, and gulfs. It is broadly distributed with greater populations existing in the outer shelf and slope regions of oceanic waters. These fish, semi-demersal in some regions and pelagic in others (due to feeding on a variety of pelagic and demersal prey), are able to survive in large estuaries, coastal areas, and open basins. Alaska pollock are limited to northern regions reflecting this species' limited temperature tolerance. They can only withstand a range of ten to twelve degrees Celsius (Bailey 1999). Common trends exhibit an age-dependent depth distribution. Fish less than one year old live throughout the water column, one-year-olds live at bottom trawls, two- to three-year-olds live higher in the column, and fish at least four years old display demersal behavior. The thermal range of these fish decreases with age. Younger fish have a greater range of temperature tolerance than older fish, which remain at lower depths where the temperature is a constant one to six degrees Celsius (Avdeev 2001).
Range depth: 1280 (high) m.
Average depth: 366 m.
Habitat Regions: polar ; saltwater or marine
Aquatic Biomes: pelagic ; benthic ; coastal
Other Habitat Features: estuarine
Theragra chalcogramma (Alaska pollock) occupies a wide geographic range and is found in a polar climate across the northern Pacific Ocean, from 68° north to 34° north, and from 129° east to 120° west (Kooka 1998). Alaska pollock inhabit a broad niche spanning the North Pacific, from the eastern Paleartic region to the western Neartic. North American populations lie along the west coast from northern California to northwest Alaska with major populations located southeast of Alaska and Canada and in the western-central Gulf of Alaska. Alaska pollock populations span the coastline of West Asia to South-West Asia and South Asia with the largest populations concentrated in the northwestern Bering Sea, the western Bering Sea, eastern Kamchatka, and the northern Sea of Okhotsk.
Biogeographic Regions: nearctic ; palearctic ; pacific ocean (Native )
Theragra chalcogramma feeds on both fish and invertebrates (Bailey 1999). The diet of this fish varies by developmental stage, season, and body size. Larvae tend to consume zooplankton such as larval copepods, while older T. chalcogramma tend to eat larger food items such as adult Acartia and Pseudocalanus. In winter, adult pollock feed mostly on fishes and euphausiid krill. In spring, T. chalcogramma feed on Appendicularia. In summer, the diet consists of euphausiids and copepods and in autumn, they feed on mainly euphausiids (Kooka 1998). Large T. chalcogramma have a diet rich in small pollock (specifically in the eastern Bering Sea) and shrimp. In areas where the juvenile population is extremely large, such as in the eastern Bering Sea, cannabalistic adults prey on the juveniles. Smaller-sized individuals are more likely to consume copepods and euphausiids (Avdeev 2001).
Animal Foods: fish; aquatic crustaceans; other marine invertebrates; zooplankton
Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)
In the Bering Sea, Theragra chalcogramma plays a key role as both predator and prey. The reproductive success of stellar sea lions is dependent on T. chalcogramma (Avdeev 2001).
Predator-prey interactions for T. chalcogramma fluctuate with seasonal conditions. One-year-old pollock occupy different areas depending on temperature. This change in local abundance affects the annual populations of other species in the region.
When infected with the parasitic copepod Haemobaphes diceraus, there is a decrease in the body weight of T. chalcogramma as well as an increase in the weight of its spleen. If T. chalcogramma is infected during the juvenile stage of development, it suffers from delayed maturity, and if it is infected as an adult, it experiences a decrease in reproductive success (Bailey 1999).
Ecosystem Impact: keystone species
Commensal/Parasitic Species:
This species is a valuable fish for fisheries on the Russian, Japanese, and Korean coasts. The fish is sold frozen, as fillets, fish sticks, surimi, and roe in Japan (Love 1996). The desire for this fish has gone up in recent years; however, it still lacks appreciation on the North Californian coast where its abundance is high. In addition to being used for food, it is also utilized for fish meal and industrial products.
Positive Impacts: food
There are no adverse effects of Theragra chalcogramma on humans (Kooka 1998).
Newly fertilized pelagic eggs of Theragra chalcogramma are approximately 3.4 mm in diameter. The eggs hatch in approximately 28 days at a temperature of three degrees Celcius. The length of each larva when it settles out is 3.8 to 5.1 centimeters (Love 1996). The larval developmental stage is considered complete within approximately 50 days. Females grow at the same rate as, or slightly faster than, males. Immature fish swim towards the surface at night to capture prey. The pre-spawning stage begins at age 2 years. Female T. chalcogramma reach maturity at three to four years at an average length of 36 centimeters, while males mature at ages four to five years (Bailey 1999).
These fish spawn in large groups. The mating system of Theragra chalcogramma consists of females releasing their eggs and then males randomly fertilizing them (Love 1996). Females are referred to as batch spawners that release eggs every few days for one month per year.
Mating System: polygynandrous (promiscuous)
Spawning of Theragra chalcogramma occurs in water depths of 90 to 200 meters. Spawning, which occurs for an entire month, is annual and the peak spawning season fluctuates from region to region. Early spawning, in the months of February, March and April, occurs in the Bering Sea. Later spawning, in the months of April, May, and June, occurs further inward over the continental slope and shelf. Spawning fish (three- to four-year-old females and four- to five-year-old males) and pre-spawning fish (two-year-old females) swim high to mid-water in dense schools. The amount of eggs that each female holds is proportional to her body size. Females of approximately 60 centimeters produce 500,000 to 600,000 eggs while females with lengths of 40 to 45 centimeters produce about one third of that. The largest of females have been known to produce up to one million eggs (Harmann 2005). Theragra chalcogramma eggs, which are transported by currents, are planktonic (Love 1996). The eggs take anywhere from 9 to 28 days to hatch.
Breeding interval: Theragra chalcogramma spawn once yearly
Breeding season: March to August in eastern Bering Sea and January to March in Aleutian Basin
Range number of offspring: 100,000 to 1,000,000.
Range gestation period: 9 to 28 days.
Range age at sexual or reproductive maturity (female): 3 to 4 years.
Range age at sexual or reproductive maturity (male): 4 to 5 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); broadcast (group) spawning; oviparous
Besides the energy put into gamete production and spawning, Theragra chalcogramma makes no investment in its offspring.
Parental Investment: no parental involvement
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.[3]
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.[4][5] 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.[6] 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.[7][8]
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.[6][9] 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.[10][11][12] 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",[13][14][15] "bigeye cod",[14] 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'[16]) or "lesser cod" (from the synonymous taxon Gadus minor) have yet to find widespread acceptance.[9] The National Oceanic and Atmospheric Administration even states that "[the common name] might never change, as common names are separate from scientific names".[9]
In addition, Norwegian pollock (Theragra finnmarchica), a rare fish of Norwegian waters, is likely the same species as the Alaska pollock.[4]
The speckled coloring of Alaska pollock makes it more difficult for predators to see them when they are near sandy ocean floors.[17] They are a relatively fast-growing and short-lived species, currently representing a major biological component of the Bering Sea ecosystem.[3] 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.[18] The Alaska pollock has well-developed drumming muscles[19] that the fish use to produce sounds during courtship, like many other gadids.[20][21]
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 60 mm (2+1⁄2 in) and fish greater than 60 mm. Both groups mainly feed on copepods.[22] However, the latter group will also forage for krill.[22] Therefore, food depletion has a larger effect on smaller pollock.[22]
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.[23]
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.[24] 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.[24]
The Alaska pollock's main habitats are the coastal areas of the Northern Pacific, especially the waters off Alaska (Eastern Bering Sea, Gulf of Alaska, Aleutian Islands) as well as off Russia, Japan and Korea (Western Bering Sea and Sea of Okhotsk). The largest concentrations of Alaska pollock are found in the eastern Bering Sea.[3]
Very small populations of fish genetically identical to Gadus chalcogrammus are found in the Barents Sea waters of northern Norway and Russia.[25] This fish was initially described as its own species under the taxon Theragra finnmarchica by Norwegian zoologist Einar Koefoed in 1956.[26] The common name used for the fish was "Norway pollock". Genetic analyses have shown that the fish is genetically identical to the Alaska pollock. It is therefore considered to be conspecific with the Pacific species and is attributed to Gadus chalcogrammus. The history of the species in the Barents Sea is unknown.[27]
The initial specification as an own species by Koefoed was based on two specimens landed in Berlevåg, northern Norway, in 1932 (hence the Norwegian name, Berlevågfisk). Based on morphological differences, Koefoed considered Theragra finnmarchica a new species, related to but separate from the Alaska pollock.[26] Just seven specimens of the fish are known to have been caught between 1957 and early 2002 in the Arctic Ocean.[28] In 2003 and 2004, 31 new specimens were caught. All specimens were large (465–687 mm (18+1⁄4–27 in) in total length) and caught in the coastal waters between Vesterålen in the west and Varangerfjord in the east. By 2006, 54 individuals had been recorded.[4] Sequencing of mitochondrial DNA of two specimens of Theragra finnmarchica and 10 Theragra chalcogramma (today: Gadus chalcogrammus) revealed no significant genetic differences, leading Ursvik et al.[29] to suggest that T. finnmarchica and T. chalcogramma are the same species. An analysis of a much larger sample size (44 T. finnmarchica and 20 T. chalcogramma) using both genetic and morphological methods led to similar conclusions.[4] While the putative species could not be separated genetically, they showed some consistent differences in morphology. Only one characteristic showed no overlap. Byrkjedal et al.[4] conclude that T. finnmarchica should be considered a junior synonym of T. chalcogramma. These analyses also suggest that T. finnmarchica is a near relative of the Atlantic cod, and that both Alaska and Norway pollock should be moved to genus Gadus.[4]
Norway pollock (Theragra finnmarchica) was listed as Near Threatened in the 2010 Norwegian Red List for Species[30] based on criteria D1: "Very small or geographically very restricted population: Number of mature individuals". The IUCN Red List currently lists Alaskan pollock as Near Threatened in Europe.[1]
The Alaska pollock has been said to be "the largest remaining source of palatable fish in the world".[32] Around 3 million metric tons (3,000,000 long tons; 3,300,000 short tons) of Alaska pollock are caught each year in the North Pacific, from Alaska to northern Japan. Alaska pollock is the world's second most important fish species, after the Peruvian anchoveta, in terms of total catch.[33]
Alaska pollock landings are the largest of any single fish species in the U.S, with the average annual Eastern Bering Sea catch between 1979 and 2022 being 1.26 million metric tons.[34] Alaska pollock catches from U.S. fisheries have been relatively consistent at approximately 1.3 million tons a year, on average 92 percent from the Bering Sea and 8 percent from the Gulf of Alaska[35].[36] Each year's quota is adjusted based on stock assessments conducted by the Alaska Fisheries Science Center to prevent overfishing.[37] For example quotas were reduced from 2008-2010 in the Bering Sea due to stock declines.[33][38]
Independent certification groups have hailed the fishery as an example of good management. For example, the Gulf of Alaska and Bering Sea/Aleutian Islands fisheries were separately certified as "sustainable" by the Marine Stewardship Council (MSC) in 2005, and were certified in 2010 and 2016.[39] The fisheries received a combined re-certification in 2020.[40] The Marine Conservation Society rates Alaska pollock harvested from the Gulf of Alaska, Bering Sea, and Aleutian Islands as sustainable, but not those from the Western Bering Sea in Russian waters.[41]
In 2021, the MSC awarded the U.S. trade associations Association of Genuine Alaska Pollock Producers (GAPP) and At-Sea Processors Association with its Ocean Champion Award that recognizes organizations for meeting MSC's commitment to a healthier ocean and a more transparent supply chain. The MSC recognized Alaska pollock from U.S. fisheries as one of the "healthiest" and "most sustainable sources" of protein.[42][43]
Compared to other cod species and pollock, Alaska pollock has a milder taste, whiter color and lower oil content.
High-quality, single-frozen whole Alaska pollock fillets may be layered into a block mold and deep-frozen to produce fish blocks that are used throughout Europe and North America as the raw material for high-quality breaded and battered fish products. Lower-quality, double-frozen fillets or minced trim pieces may also be frozen in block forms and used as raw material for lower-quality, low-cost breaded and battered fish sticks and portions.
A life-cycle assessment on the carbon footprint of Alaska pollock, performed by a sustainability consulting firm, showed that Alaska pollock fillet has a lower carbon footprint and delivers more protein per kilogram of greenhouse gas emissions than many other animal proteins, including beef, chicken, cod, and even plant-based options.[44][45]
Alaska pollock is commonly used in the fast food industry in products such as McDonald's Filet-O-Fish sandwich,[46][47] Burger King Big Fish Sandwich, Wendy's Crispy Panko Fish Sandwich,[48] Arby's King's Hawaiian Fish Deluxe,[49] Arby's Crispy Fish Sandwich,[50] Arby's Spicy Fish Sandwich,[51] Long John Silver's Baja Fish Taco,[52] Bojangles Bojangular,[53] Birds Eye's Fish Fingers in Crispy Batter,[54] 7-Eleven's Fish Bites,[55] White Castle's Panko Breaded Fish Sliders,[56] and Captain D's Seafood Kitchen.[57] Some of these items are seasonal offerings to coincide with the Lent calendar where seafood demand is higher.
Single-frozen Alaska pollock is considered to be the premier raw material for surimi. The most common use of surimi in the United States is "imitation crabmeat", though it is often seen labeled in retailers and grocers as "surimi seafood" sticks, flakes, or chunks.[58][59] There are five main forms of surimi seafood: chunk, leg, flake, salad, and shred.[60] Surimi made from minced Alaska Pollock retains the aforementioned carbon footprint advantage.[44][61]
Pollock roe is a popular culinary ingredient in Korea, Japan, and Russia. In Korea, the roe is called myeongnan (명란, literally 'Alaska pollock's roe'), and the salted roe is called myeongnan-jeot (명란젓, literally 'pollock roe jeotgal'). The food was introduced to Japan after World War II, and since has been called mentai-ko (明太子) in Japanese. A milder, less spicy version is usually called tarako (鱈子, literally 'cod's roe'), which is also the Japanese name for pollock roe itself. In Russia, pollock roe is consumed as a sandwich spread. The product, resembling liquid paste due to the small size of eggs and oil added, is sold canned.
Alaska pollock is considered the "national fish" of Korea.[62][63] The Korean name of the fish, myeongtae (명태,明太), has also spread to some neighbouring countries: it is called mintay (минтай) in Russia and its roe is called mentaiko (明太子) in Japan, although the Japanese name for the fish itself is suketōdara (介党鱈). In Korea, myeongtae is called thirty-odd additional names, including saengtae (생태, fresh), dongtae (동태, frozen), bugeo (북어, dried), hwangtae (황태, dried in winter with repeated freezing and thawing), nogari (노가리, dried young), and kodari (코다리, half-dried young).[63]
Koreans have been eating Alaska pollock since the Joseon era. One of the earliest mentions is from Seungjeongwon ilgi (Journal of the Royal Secretariat), where a 1652 entry stated: "The management administration should be strictly interrogated for bringing in pollock roe instead of cod roe."[64] Alaska pollocks were the most commonly caught fish in Korea in 1940, when more than 270,000 tonnes were caught from the Sea of Japan (East Sea).[65] It outnumbers the current annual consumption of Alaska pollock in South Korea, estimated at about 260,000 tonnes in 2016.[66] Nowadays, however, Alaska pollock consumption in South Korea rely heavily on import from Russia, due to rises in sea water temperatures.[67] In 2019, South Korea imposed a total ban on pollock fishing "to help replenish depleted stocks" of the fish.[68]
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.
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