Is the poleward expansion by Atlantic cod and haddock threatening native polar cod, Boreogadus saida?

• DOI: 10.1007/s00300-011-1085-z
• Publication Date: 2011-09-14T03:00:45Z
• Authors: Paul E. Renaud; Jørgen Berge; Øystein Varpe; Ole Jørgen Lønne; Jasmine Nahrgang; Camilla Ottesen; Ingeborg Hallanger
• Keywords: 0106 biological sciences; 14. Life underwater; 01 natural sciences

During a recent period of increased influx of warm Atlantic water to the western coast of Svalbard, we have observed a northward expansion of boreal Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) into areas dominated by the native polar cod (Boreogadus saida). To determine the potential impact of new ecological interactions, we studied the diet of co-occurring juvenile gadoids in fjords, open water, and sea ice around Svalbard. We also reviewed the available literature on polar cod feeding in different habitats across the Arctic to determine whether region, habitat, or fish size may influence diet. Feeding by polar cod in the pelagic zone was size dependent, with small fish primarily consuming Calanus spp. and smaller copepods, with an increasing ration of Themisto spp. at larger sizes. In benthic habitats, diets were more varied and included considerably more unidentified material and sediment. Less than 40% dietary overlap was detected among the three species when they were found together. Stable isotope analyses indicated these patterns were representative of longer-term assimilation. The low interspecific dietary overlap suggests little direct competition. Future increases in abundance and the high predation potential of the boreal taxa, however, may impact the persistence of polar cod on some Arctic shelves.