Alaska Pollock (Gadus chalcogrammus)

Physical Characteristics

The Alaska pollock is a schooling, semi-pelagic fish species belonging to the Gadidae family, distributed in the North Pacific Ocean, with particularly dense populations in the East Bering Sea, where it spends most of its life swimming in the water column, descending to the seafloor to spawn or feed.

This species can reach a length of 90 cm and a weight of 4 kg. When resting on sandy ocean bottoms, its mottled pattern resembling a near design makes it harder for predators to spot. The Alaska pollock possesses well-developed specialized muscles, like some other cod species like, which it uses to produce sounds during weave. Its dorsal fins are widely spaced. The ventral fins have a slightly elongated filament. The head contains side line pores. The back is colored in shades of greenish-brown, the sides are silvery, and the belly is typically lightened by mottled patterns or spots color.

Habitats, Reproduction, and Feeding

The distribution range of the Alaska pollock includes coastal areas of the North Pacific, particularly the eastern Bering Sea off Alaska, the Gulf of Alaska, and the Aleutian Islands, as well as the Bering and Okhotsk Sea waters off Russia, Japan, and Korea.

The Alaska pollock is a keystone species in North Pacific ecosystems due to its influence on both upper and lower trophic levels. For example, some science researchers have linked the decline of this species to population crashes of Steller sea lions in the Gulf of Alaska, seabird mortality events, and broader, more complex changes in ecosystem structure. It is also a major predator and competes with humans for valuable prey such as shrimp and juvenile salmon. From this perspective, the population dynamics of the Alaska pollock are considered to regulate its ecosystems both top-down and bottom-up.

Individuals reach maturity at 3 to 4 years of age, and each female produces millions of eggs per spawning season. Approximately fixed eggs are spawned per spawning event annually. A single female can complete the release of all her eggs over about 14 separate occasions within a one-month period. The eggs are spherical, approximately 1 mm in diameter. Larvae hatching from these eggs can survive for about one week by relying on their yolk sacs. Another key step in the reproductive process is the selection of spawning grounds. Alaska pollock larvae are very weak swimmers during their first few weeks of life and cannot effectively swim against strong Alaska currents. Consequently, adults tend to spawn on the continental shelf, in areas with favorable oceanographic conditions that minimize larval dispersal by strong currents. As a result, Alaska pollock migrate toward shallow waters on the continental shelf in spring to spawn and feed, and return to warmer, deeper waters during winter months. Sexual maturity is reached at a size of 30 to 35 cm. This fish, which grows slowly and is short lived, has an estimated lifespan of about 12 years.

The primary factor influencing the nutrition behavior of the Alaska pollock is size. In this regard, individuals smaller than 6 cm can be distinguished from larger ones as two subgroups. Both groups primarily feed on copepods, but the larger subgroup also feeds on krill. Therefore, declines in the abundance of these prey species represent a significant factor affecting the survival rates of smaller individuals.

Fishing and Culinary Uses

The Alaska pollock is often described as “the world’s last great source of flavorful fish.” Approximately 3 million tons of Alaska pollock are caught annually in the North Pacific, from Alaska to northern Japan. It is the second most important fish species in global fisheries after the Peruvian anchoveta. USA, Japan, and Russia are the main countries harvesting this species. In the United States, approximately 1.5 million tons are caught annually, mostly from the Bering Sea. According to stock assessment studies conducted by the Alaska Fisheries Science Center, annual catch quotas are set. For example, following a sudden stock decline in 2008, quotas were reduced for the 2009 and 2010 fishing seasons, and as a result of these adjustments, fishing levels returned to average by 2011.

The filleted and frozen form of this species, as well as its processed form known as surimi (a type of dough made from fish or other seafood meats), and its roe, are widely consumed in Korean, Japanese, and Russian cuisines. The Alaska pollock is considered a traditional Korean national fish and has been consumed for centuries, dating back to at least 1400–1900.