Pollock is the most abundant and widely distributed representative of cod fish in the Pacific Ocean. It inhabits the North Pacific costal waters. The northern border of its distribution runs in the Chukchi Sea to the north, it penetrates along North America to the Monterey Gulf, and along the Asian coast to the northern part of the Korea Strait. Here large and abundant North Okhotsk and East Bering super populations have their habitation.
The nucleus of the North Okhotsk super population is situated in the North-Eastern Sea of Okhotsk, which is the main area of Pollock reproduction, where in certain years 80% of the season’s spawned roe and breeders are concentrated, as well as 90% of fry fish. The western Sea of Okhotsk is inhabited by peripheral groups. Due to the differentiation of the super-population areal into the reproduction and feeding part including practically the entire sea water area, Pollock uses feeding resources of sea areas less favorable for reproduction.
Rather large are West Alaska, Olyutorsky-Karaginsky, and East Kamchatka and East Korea populations. There are also many small populations, which include Pollock of the Peter the Great Bay, four groups around Hokkaido Island, Tatar Strait, Commander Islands, East Alaska and Vancouver populations. Isolation of other population groups can only be discussed presumably.
Fig. General diagram of Pollock population structure (Shuntov et al, 1993).
The summary biomass of populations: а– up to 10 million tons and more, b – from several hundred thousand to several million tons, c - from several ten thousand to several hundred thousand tons. The arrows show the Pollock travel paths. The light circles are autumn or winter spawning and dark ones are the spring spawning. Populations: East Korean (1), Peter the Great Bay (2), Shimana (3), Toyama (4), West Hоккаido (5), Tatar Strait (6), South Hоккаido (7), East Hоккаido (8), South Kuril (9), North Hоккаido or Raus (10), North Okhotsk Sea super population (11), East Kamchatka (12), Commander (13), Olyutorsky-Karaginsky (14), Koryak (15), East Bering Sea super population (16), East Aleutian (17), West Alaska (18), East Alaska (19), Vancouver (20)
Pollack of Northern groups is characterized by the high migration activity, while migration paths of southern groups are relatively shorter. Pollock of northern populations propagates mainly in spring, while southern populations do the same in the autumn (Korean waters), but more often in winter. The southern, especially the south-western part of the areal, is inhabited by many population groups, which is related with adaptations to the complex structure of waters and streams in this area that is located at the junction of moderate and subtropical zones.