Norwegian Coastal Cod Research Articles

Differences in growth performance between Arcto-Norwegian and Norwegian coastal cod reared under identical conditions

Offspring from seven family groups of Arcto-Norwegian cod (AN) and a genetically marked Norwegian coastal cod (NC) broodstock, were mixed at metamorphosis and raised in the same rearing unit. The fish were transferred subsequently to a net-pen and held under standard farming conditions. In December 1992, 466 cod juveniles were measured, weighed, and tagged individually. Length and weight changes were monitored until the fish matured (January 1994). Genotyping of each individual was performed using enzyme electrophoresis to identify the fish to strain. Prespawning females were examined for organ weights and stage of maturity. There were population specific Differences in growth performance. NC displayed significantly higher specific growth rate (SGR) and daily length increment (DLI) during spring/summer season. The AN had significantly lower hepatosomatic and gonadosomatic indices, and were thinner than the NC, indicating Differences in body form and energy allocation pattern between the two strains. All NC (both sexes) became sexually mature at the age of 2 years while 2% of fish in the AN group were still immature at the end of the experiment.

Differences in growth performance between Arcto‐Norwegian and Norwegian coastal cod reared under identical conditions

Offspring from seven family groups of Arcto‐Norwegian cod (AN) and a genetically marked Norwegian coastal cod (NC) broodstock, were mixed at metamorphosis and raised in the same rearing unit. The fish were transferred subsequently to a net‐pen and held under standard farming conditions. In December 1992, 466 cod juveniles were measured, weighed, and tagged individually. Length and weight changes were monitored until the fish matured (January 1994). Genotyping of each individual was performed using enzyme electrophoresis to identify the fish to strain. Prespawning females were examined for organ weights and stage of maturity. There were population specific Differences in growth performance. NC displayed significantly higher specific growth rate (SGR) and daily length increment (DLI) during spring/summer season. The AN had significantly lower hepatosomatic and gonadosomatic indices, and were thinner than the NC, indicating Differences in body form and energy allocation pattern between the two strains. All NC (both sexes) became sexually mature at the age of 2 years while 2% of fish in the AN group were still immature at the end of the experiment.

Coastal cod in Northern Norway

Northeast Arctic cod dominates the Norwegian cod fisheries, but a significant part of the landings are Norwegian coastal cod. In the past, landings of coastal cod by Norway have been estimated to be ∼5% of the total international cod landings north of 62°N. In contrast to Northeast Arctic cod, the coastal cod is restricted mainly to fjords and coastal areas. The coastal cod is distinguished from Northeast Arctic cod by the growth zones of the otoliths, but there is often doubt about the classification. In 1980–1983, a research program on coastal cod in northern Norway was carried out. The program was concentrated on five major fjord systems. Sampling and tagging of cod was carried out on the spawning grounds during the spawning seasons. In addition, some tagging of immature fish was carried out on the coast in autumn. Northeast Arctic cod occurred only in low numbers on the fjord spawning grounds, usually <5% of the total. Samples of cod, mostly immature, from the coast generally contained a higher proportion of Northeast Arctic cod, between 5 and 25%. The coastal cod tend to return to the same spawning grounds year after year, but some leave the fjords during the feeding season. Problems of defining a stock are discussed. Although the relationship between Northeast Arctic cod and coastal cod is unclear, the regularity in the spawning in at least some of the fjords indicates that they contain populations which are, to a large extent, self sustained.

Growth and Maturation of Norwegian coastal cod and Northeast Arctic cod under different conditions

The Norwegian coastal cod and the Northeast Arctic cod have been considered as two populations which can be separated by otolith studies. They are, in addition, characterized by differences in growth, age at first spawning and migration pattern. The environmental conditions under which the two groups live before maturation differ considerably. In this paper, growth and age at first spawning of cod from both groups, as well as of progeny from crossings between them, were studied under controlled laboratory conditions. The results show that growth increased and age at first spawning decreased considerably under favourable laboratory conditions compared to observations in the field. It is further indicated that the differences in growth and age at first spawning for coastal and Northeast Arctic cod reflect differences in the environment rather than genetic variations.