Cod-capelin-polar cod interaction

Cod, polar cod and capelin. Photo: Geir Wing Gabrielsen, Norwegian Polar Institute

Interactions, drivers and pressures 2018
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The interaction cod-capelin-polar cod is one of the key factors regulating the state of these stocks. Cod prey on capelin and polar cod, and the availability of these species for cod varies. Сod can strongly influence on numbers of these species. In the years when the temperature was close to the long-term mean, the cod overlap with capelin and polar cod was lower than in the recent warm years. Cod typically consume most capelin during the capelin spawning migration in spring (quarters 1+2), but especially in recent years the consumption has been high also in autumn (quarters 3+4) in the northern areas (Figure 4.2.3). In 2017-2018 capelin consumption by cod was stable.

With the recent warming of the Barents Sea, the cod stock increased and became distributed over larger area, overlapping with capelin and especially polar cod to a higher degree than before. Cod can prey intensely on polar cod. The polar cod are most likely more available for cod than the capelin in mix concentration, because they possibly have a lower swimming speed (confirmed by trawl catch analyses) and are distributed closer to the bottom. However, capelin is a fatter and energetically more valuable prey item. It should be noted, that the polar cod biomass in the Barents Sea is substantially less than the capelin bimass, thus, the effect of cod consumption on the stocks of these fish is different. Besides, that the length of the period with cod and polar cod overlap is much shorter (September-December) compared to the overlapping time of cod and capelin. Thus, interspecific interactions in this trophic system are very complex and require more detailed study.