Cod-capelin-polar cod interaction

Interactions, drivers and pressures 2016
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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. 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).

A decline in the consumption of capelin by cod was observed in the second half of 2015 and in 2016, but the decline is less strong than indicated by the decline in the stock estimates.

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, especially in mixed (polar cod and capelin) concentrations. The polar cod are most likely more available for cod than the capelin, because they possibly have a lower swimming speed (confirmed by trawl catch analyses) and are distributed closer to the bottom. However, capelin is fatter and energetically more valuable prey item. It should be noted, however, 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.