Foraging ecology of ringed seals (Pusa hispida), beluga whales (Delphinapterus leucas) and narwhals (Monodon monoceros) in the Canadian High Arctic determined by stomach content and stable isotope analysis

Stomach content and stable isotope analysis (δ¹³C and δ¹⁵N from liver and muscle) were used to identify habitat and seasonal prey selection by ringed seals (Pusa hispida; n=21), beluga whales (Delphinapterus leucas; n=13) and narwhals (Monodon monoceros; n=3) in the eastern Canadian Arctic. Arctic cod (Boreogadus saida) was the main prey item of all three species. Diet reconstruction from otoliths and stable isotope analysis revealed that while ringed seal size influenced prey selection patterns, it was variable. Prey-size selection and on-site observations found that ringed seals foraged on smaller, non-schooling cod whereas belugas and narwhals consumed larger individuals in schools. Further interspecific differences were demonstrated by δ¹³C and δ¹⁵N values and indicated that ringed seals consumed inshore Arctic cod compared to belugas and narwhals, which foraged to a greater extent offshore. This study investigated habitat variability and interseasonal variation in the diet of Arctic marine mammals at a local scale and adds to the sparse data sets available in the Arctic. Overall, these findings further demonstrate the critical importance of Arctic cod to Arctic food webs.