Claws, climate change, and the Canadian Arctic: Spatiotemporal variation in ringed seal and bearded seal diet and mercury exposure

Abstract

Climate change is disproportionately affecting the Arctic, causing a decrease in sea ice extent and thickness, which in turn impacts interspecific interactions and food availability for marine organisms. This thesis focused on two higher trophic level predators: ringed seals (Pusa hispida, Natsiq) and bearded seals (Erignathus barbatus, Ujjuk), both of which rely on sea ice and are vulnerable to environmental changes that influence the base of the food web and to bioaccumulative toxicants like mercury. Using stable isotopes (δ13C, δ15N, δ34S) and total mercury (THg) in seal claws, this study investigated spatiotemporal variability in foraging ecology and mercury concentrations of ringed seals and bearded seals in relation to latitudinal differences and decadal changes in sea ice cover, environmental conditions, and biological factors. Samples were collected between 1990 and 2020 during Inuit subsistence harvests in Kugaaruk, Sanikiluaq, and Pangnirtung, Nunavut. Seals at lower latitudes had lower THg levels, fed more pelagically and at a lower trophic level, and showed greater individual specialization than seals at higher latitudes. Seals consumed relatively more pelagic prey in years with longer open water periods, adding to a growing body of evidence of climate-induced shifts in the foraging strategies of Arctic marine mammals towards pelagic prey. The analysis of ringed seal diets and mercury exposure from 1982 to 2018 in Cumberland Sound showed increased consumption of higher trophic level prey during years with less sea ice and longer open water periods, while δ34S and THg decreased over time, suggesting increased consumption of lower trophic level fish. The isotopic niche of ringed seals expanded from 1982 to 2018, indicating a broader resource use that may include more benthic-associated species. This study provided valuable insight into spatial and temporal variation in foraging strategies and contaminant exposure of two Arctic marine predators; information which contributes to understanding marine ecosystem health and resilience in the face of climate change.