Arctic seals as tracers of environmental and ecological change

Abstract

Knowledge of species trophic position (TP) is an essential component of ecosystem management. Determining TP from stable nitrogen isotopes (δ¹⁵N) in predators requires understanding how these tracers vary across environments and how they relate to predator isotope composition. We used two seal species as a model for determining TP across large spatial scales in the Arctic. δ¹⁵N in seawater nitrate (δ¹⁵N_NO3) and seal muscle amino acids (δ¹⁵N_AA) were determined to independently characterize the base of the food web and the TP of harp and ringed seals, demonstrating a direct link between δ¹⁵N_NO3 and δ¹⁵N_AA. Our results show that the spatial variation in δ¹⁵N_AA in seals reflects the δ¹⁵N_NO3 end members in Pacific vs. Atlantic waters. This study provides a reference for best practice on accurate comparison of TP in predators and as such, provides a framework to assess the impact of environmental and human‐induced changes on ecosystems at pan‐Arctic scales.