Interspecific interactions may be altered as a result of poleward species range shifts caused by climate change. In recent decades, Cumberland Sound, Nunavut, in the Canadian Arctic, has undergone concurrent increases in the availability of the forage fish capelin (Mallotus villosus) and the number of migratory harp seals (Pagophilus groenlandicus) during the open-water period; however, the impacts of these changes on endemic Arctic species, such as ringed seals (Pusa hispida), have received little attention. We coupled stomach contents with stable isotope analysis (delta C-13 and delta N-15) of muscle and liver to determine the extent of potential competition between ringed seals (n=91) and harp seals (n=39) in Cumberland Sound. Isotopic niche breadth was greater for ringed seals (95% ellipse: 10.08 parts per thousand(2)) than for harp seals (95% ellipse: 8.00 parts per thousand(2)), and harp seal isotopic niche overlapped more with ringed seal isotopic niche than vice versa, suggesting asymmetrical competition potential. Although there was high overlap in isotopic niche breadth (range 50.3-91.0%) and prey species consumed (Schoener's Index 0.60), stomach content analysis revealed differences in prey species proportions and size composition, thereby reducing the degree of realized niche overlap. Harp seals consumed a higher biomass of fish (66.7%) than did ringed seals (31.9%), and harp seals also consumed larger capelin (64-200mm), polar cod (Boreogadus saida; 28-194mm), and Liparidae (55-115mm) than ringed seals (63-154mm, 20-189mm, and 16-128mm, respectively). With climate change and range shifts predicted to continue into the future, our results provide an important baseline for future studies examining interspecific interactions.
Ogloff, Wesley R.,Yurkowski, David J.,Davoren, Gail K.,et al. Diet and isotopic niche overlap elucidate competition potential between seasonally sympatric phocids in the Canadian Arctic[J]. MARINE BIOLOGY,2019-01-01,166(8)