Resource-driven colonization by cod in a high Arctic food web

Climate change is commonly associated with many species redistributions
and the influence of other factors may be marginalized, especially in the
rapidly warming Arctic. The Barents Sea, a high latitude large marine
ecosystem in the Northeast Atlantic has experienced above average
temperatures since the mid 2000’s with divergent bottom temperature trends
at sub-regional scales. Concurrently, the Barents Sea stock of Atlantic
cod Gadus morhua, one of the most important commercial fish stocks in the
world, increased following a large reduction in fishing pressure and
expanded north of 80°N. We examined the influence of food availability and
temperature on cod expansion using a comprehensive data set on cod stomach
fullness stratified by sub-regions characterized by divergent temperature
trends. We then tested whether food availability, as indexed by cod
stomach fullness, played a role in cod expansion in sub-regions that were
warming, cooling or showed no trend. The greatest increase in cod
occupancy occurred in three northern sub-regions with contrasting
temperature trends. Cod apparently benefited from initial high food
availability in these regions that previously had few large-bodied fish
predators. The stomach fullness in the northern sub-regions declined
rapidly after a few years of high cod abundance, suggesting that the
arrival of cod caused a top down effect on the prey base. Prolonged cod
residency in the northern Barents Sea is, therefore, not a certainty.