| Summary: | Arctic ecosystems are changing at an alarming rate, with the Arctic Ocean predicted to be summer sea ice free within the next few decades. Beluga whales (Delphinapterus leucas) are the most abundant Arctic odontocete, exhibiting a circumpolar distribution and a strong association to sea ice, and are thus a sentinel species for the effects of climate change. The vulnerability of belugas to changing environmental conditions will depend on their adaptive capacity and resilience to changes in the prey base. The overall objective of my thesis was to examine the potential effects of prey shifts due to changing environmental conditions on Beaufort Sea beluga whales by examining relationships among body condition, dietary tracers, and physiology. Differences in lipid content and carbonates in the tissues of beluga and their potential prey affected both carbon (δ13C) and nitrogen (δ15N) stable isotope ratios, which could lead to incorrect ecological interpretations. Inter-annual variation in blubber fatty acid signatures and liver δ13C and δ15N values in beluga whales may be related to annual differences in environmental conditions and abundances of Arctic cod (Boreogadus saida). To establish an effective approach for identifying prey, I used Bayesian mixing model Fatty Acid Source Tracking Algorithm in R (FASTAR) to reconstruct the known diets of two captive beluga whales using fatty acid signatures. FASTAR was then used to reconstruct the offshore diets of Beaufort Sea belugas. Although diets varied annually, Arctic cod and capelin (Mallotus villosus) were identified as the main prey of belugas. Finally, I examined physiological limits and the relationships between body condition and physiological parameters pertaining to oxygen storage capacity in belugas. Males had higher oxygen stores than females due to larger body size and higher hemoglobin concentrations. Body condition indices positively correlated with myoglobin and hemoglobin concentrations, and hematocrit, resulting in lower calculated aerobic dive limits in ...
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