| Summary: | In several sub-arctic marine ecosystems of the North Atlantic capelin are the primary prey item for cod, and the trophic interaction between capelin and cod is a central energetic pathway. However, in the North Pacific capelin are, in spite of their high abundance, barely represented in the diet of cod. In the Bering Sea this uniquely weak trophic link is the consequence of oceanic landscape features (e.g., bathymetry, hydrography, currents, and presence of suitable spawning areas) that generate a barrier between the centers of distribution of cod and capelin. Climate forcing influences labile features of this distributional barrier (i.e., hydrography) and may result in greater/lower predator-prey overlap through the opening of thermal gateways and corridors. In the current study we compare the results from the Bering Sea with those from the Barents Sea, where cod are strongly dependent on capelin as prey. Through this comparative analysis we wish to illustrate the importance that oceanic landscape and climate forcing have on the spatial overlap and trophic interactions between predator and prey. Spatial considerations are seldom accounted for in population dynamics models, even though the mechanisms that promote overlap variability can indirectly have profound effects on population demographic rates. In that regard we believe that our analysis is relevant to better comprehend the mechanisms leading to regime shift of marine forage population dynamics in the presence of climate forcing.
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