Pacific cod – Gadus macrocephalus                 

Diagnostic features
Head relatively broad; interorbital space 18 to 25% of head length. Predorsal distance more than about 33% of length; anterior part of swimbladder with 2 relatively short, horn-like extension.  Colour: dorsally brown to grey with spots or vermiculations, ventrally paler.  

Geographical Distribution 
Found around the rim of the North Pacific, from the Yellow Sea to the Bering Strait, along the Aleutians, and south to about Los Angeles. Rather rare in the southern part of its range.

Pacific cod - Geographical distribution

Habitat and Biology 
Lives mainly along the continental shelf and upper slope of the North Pacific in the areas bordered by Korea and the western Chukchi Peninsula in the west, and Norton Sound and Oregon in the east. Its bathymetric range extends from shallow water (10 m) to about 550 m, but it is mostly between 100 and 400 m in the Gulf of Alaska and the Bering Sea.  Some cod are assumed to be pelagic over deep water.

Spawning migrations have been definitely linked to annual changes in temperature of the ocean in various parts of the geographical range. Pacific cod does not undertake migrations as extensive as the Atlantic species but moves only for short distances, such as to and from the shore, or from one bank to the other within a limited region.

Fecundity ranges from 860,000-6,400,000 eggs per individual, depending also on environmental conditions: in the far eastern areas, the range is 1,400,000-6,400,000 eggs; in Hokkaido waters, 3,000,000-4,000,000 eggs; in Mutsu Bay (northernmost Honshu), 1,500,000-2,000,000 eggs. In the Straits of Georgia (southern British Columbia), females of 60-78 cm produce 1,200,000 to 3,300,000 eggs; in the Gulf of Alaska the fecundity ranges from 860,000-3,000,000 eggs, and in the Bering Sea, from 1,000,000-2,000,000 eggs. Females spawn only once each season. The eggs are demersal and slightly adhesive. The spawning season extends from winter to early spring.

In the western Pacific, around the Commander Islands and along the coast of Siberia, spawning occurs from January to May. Spawning time differs between Japan and the Sea of Okhotsk because of differences in the cycles of the oceanographic climate: in the warmer regions such as Japan and Korea, the fish remain at greater depths during summer (up to 200 m), and when temperatures drop during autumn, they move into shallow water, and spawn during winter; in more northern regions, such as the Sea of Okhotsk, where the temperatures of littoral waters are very low during winter, cod move to considerable depths for over-wintering and spawn in March-April.

Spawning in the eastern Bering Sea is expected to take place within the period of January to April, when water temperature is higher than 0°C; the optimum temperature for hatching and survival is considered to be 5°C.

Growth of Pacific cod is rapid during early stages. In the eastern Bering Sea, it has not been well identified because of problems in ageing the fish in the region. The southern Pacific stocks grow substantially faster than stocks of the colder regions of the North Pacific (such as the Bering and Okhotsk Seas), and growth is continuous throughout the year. Southern Pacific cod also mature at an earlier age and have a shorter life span (6-7 years).

Size 
Reaches 1 m total length.

Fisheries 
The Japanese catch in Northeast Pacific (area 61), which had traditionally accounted for the largest component of the total landings of this species, has decreased substantially (because of intense exploitation) since the mid seventies, while the Russian Federation (formerly USSR) catch has shown a rapid increase in recent years. It should be noted that the abundance of Pacific cod has increased substantially since 1977 as a result of the recruitment of the exceptionally strong year classes for 1977-1978 and the good year classes of 1982 to 1985.

Pacific cod is often taken incidentally by pollock and flatfish fisheries, and in Korea it is exclusively a by-catch of other commercial fisheries. In northeastern Pacific, the major types of gear used are trawls, but also longlines, troll and handlines. In Japan and Bering Sea, also Danish seines, and pair trawl and stern trawl are used. In all areas, the importance of cod in the catches declines with depth. Depths of greatest cod occurrence were generally between 91 and 273 m. There are higher proportions of large fish in the British Columbia and southeastern Alaska regions than in the Gulf of Alaska and the Bering Sea. In the eastern Bering Sea, cod are taken primarily on the outer continental shelf (about equally divided between the areas southeast and northwest of the Pribilof Islands), with highest catches occurring near the shelf edge. Pacific cod has a high growth rate and high natural mortality and can support heavy exploitation. The catch is used mostly for filleting for subsequent production of fish sticks and fillet blocks.

Source: FAO