Insight into the diet history of ice seals using isotopic signatures of muscle tissue and claws

Abstract

Climate change and sea ice reduction in the Arctic may impact foraging of ice-associated predators. The goal of my thesis work was to examine interannual differences in the diet of ringed, bearded, spotted, and ribbon seals as described by stable nitrogen and carbon isotope ratios of muscle tissue and claws to assess foraging plasticity. Isotopic mixing models from muscle data were used to describe the proportional contribution of prey groups during 2003, 2008-2010. Results showed a higher proportional contribution of smelt (Osmeridae) and benthic prey to ringed and bearded seal diets in 2003 compared to 2008-2010. Seasonal keratin layers deposited in claws can document trophic history up to about 10 years. During 2007 (record ice minimum), proportionally more ringed seals fed at a lower trophic level, while spotted seal adults and young-of-the-year fed at a lower trophic level during 2006. Bearded seals may have been foraging more pelagically from 2008 to 2010. Ice seals may be taking advantage of more abundant pelagic crustaceans as the Arctic ecosystem changes to a pelagic-dominated food web. Interannual variations and high variability among species and individual diets illustrate the opportunistic nature and flexibility of ice seals to changes in prey composition.