Stable isotopes (15N and 13C) in dentine growth layer groups (GLGs) of narwhal embedded teeth

Monitoring Arctic marine mammals in response to rapid climate change requires reliable longitudinal data. To obtain such data is challenging, but sequential measurements of stable isotopes (SI) from metabolically inert tissues like dentine allow for chronological reconstruction of SI data that can provide insights into whale life history, behaviour, and physiology. This study examined dentine samples from narwhal embedded canines to reconstruct individual SI profiles and assess intra-annual variation in 15N and 13C. The individual 15N and 13C profiles of all 31 narwhals exhibited cyclical oscillations. The majority of 15N and 13C oscillations (>50%) occurred within the annual growth layer groups (GLGs), suggesting seasonal variation. The mean magnitude of SI oscillations per individual ranged from 0.4 to 2.5 for 15N and 0.2 to 1.1 for 13C. Such intra-annual SI oscillations may reflect variability in narwhal ecology related to environmental variation (e.g., seasonal changes in baseline SI and diet associated with narwhal migration) and/or changes in narwhal physiology (e.g., seasonal energetics), highlighting the utility of SI profiles for long-term monitoring of narwhals ecological and physiological responses to a changing Arctic.Narwhal embedded canines were collected by Inuit during subsistence hunts near Pond Inlet and provided to Fisheries and Oceans Canada through a voluntary collaborative sampling program with the Pond Inlet Hunters and Trappers Association. These harvested narwhals belonged to the Baffin Bay narwhal population, which is monitored by DFO for stock assessment. This research adds to our understanding of this population in terms of their vulnerability and variability to the changing Arctic conditions.