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.

Data from the Joint Russian Norwegian Ecosystem survey in the Barents Sea. The data are aggregated by sub-regions, see file data_script.txt and main paper for explanation. The raw data at the station level sampled by Norwegian boats at the surveys can be obtained from the Institute of Marine Research, Norway upon reasonable request. Special legal restrictions apply to Russian raw data. These can only be shared under contracted agreements.