Spatial, temporal and within-species variation in the foraging ecology among consumers add to the complexities of trophic structure and its processes across all biomes on Earth. In this dissertation, I investigated the foraging ecology and plasticity of an ice-adapted marine predator, the ringed seal (Pusa hispida), inhabiting the Arctic marine environment – a dynamic seascape undergoing rapid climatic changes – across age, space and time using stable isotope analysis and animal satellite telemetry. I used a long-term dataset (1990 – 2013) of ringed seal muscle (n = 630) and liver (n = 558) samples, as well as satellite telemetry data (1999-2013; n= 132) collected from seven locations across the Arctic of varying latitude (56ºN – 76ºN) and longitude (-117ºW – -61ºW). I first quantified the general increase in δ13C and δ15N values of three tissues from eight arctic marine mammal species after chemical lipid extraction with results varying across species, developed species- and tissue-specific lipid normalization models, and a species-tissue-specific decision framework for the best lipid correction approach. I then quantified spatial and temporal variation of ringed seal dietary prey contributions, isotopic niche size and trophic position during ontogeny across the Arctic. I found a general latitudinal trend where the level of fish consumption and trophic position of ringed seals decreased due to increased prevalence of sub-arctic fish species and less trophic complexity in the zooplankton community at lower latitudes. As well, isotopic niche size for ringed seals and beluga whales (Delphinapterus leucas) increased at lower latitudes and level of individual specialization in ringed seals increased at lower latitudes as a response to large-scale spatial variation in ecological opportunity (i.e. prey species richness) which is higher at lower latitudes. Using satellite telemetry, I found that individuals from higher latitudes, which undergo shorter ice-free seasons, spend more time traveling and less time foraging than individuals from lower latitudes where the ice-free season is longer. Also, smaller individuals spent more time transiting between habitat patches than their larger conspecifics due to competitive exclusion. Overall, these findings highlight the foraging plasticity of ringed seals to changing environmental conditions and resource availability
