Trophic ecology of sympatric Arctic gadoids, Arctogadus glacialis (Peters, 1872) and Boreogadus saida (Lepechin, 1774), in NE Greenland

Two gadoid fishes, Arctogadus glacialis and Boreogadus saida, often coexist (i.e. sympatric) in the fjords and shelf areas of the Arctic seas, where they likely share the same food resources. Diet composition from stomach contents, i.e. frequency of occurrence (FO) and Schoener's index (SI), and stable isotope signatures (delta C-13 and delta N-15) in muscle of these sympatric gadoids were examined from two fjords in NE Greenland-Tyrolerfjord (TF, similar to 74A(0)N, sill present) and Dove Bugt (DB,similar to 76A(0)N, open). Twenty-three prey taxa and categories were identified and both gadoids ate mostly crustaceans. The SI values of 0.64-0.70 indicated possible resource competition, whereas FO differed significantly. A. glacialis fed mainly on the mysid Mysis oculata and other benthic-associated prey, whereas B. saida ate the copepod Metridia longa and other pelagic prey. Both diet and stable isotopes strongly suggest a spatial segregation in feeding habitat, with A. glacialis being associated with the benthic food web (mean delta C-13 = -20.81aEuro degrees, delta N-15 = 14.92aEuro degrees) and B. saida with the pelagic food web (mean delta C-13 = -21.25aEuro degrees, delta N-15 = 13.64aEuro degrees). The dietary differences and isotopic signals were highly significant in the secluded TF and less clear in the open DB, where prey and predators may be readily advected from adjacent areas with other trophic conditions. This is the first study on the trophic position of A. glacialis inferred from analyses of stable isotopes. The subtle interaction between the Arctic gadoids should be carefully monitored in the light of ocean warming and on-going invasions of boreal fishes into the Arctic seas.