Assessing the Relationship Between Blubber Thickness and Adipocyte Size in Beluga Whales

Body condition, the relative amount of energy reserves in an individual, reflects nutritional status and overall health in marine mammals and can indicate the influence of stressors on individuals. Energy in marine mammals is primarily stored as lipids within adipocytes in blubber tissue, making blubber thickness a common proxy for body condition. However, blubber also serves structural roles, complicating its use as a body condition indicator. Our objective was to assess the relationship between adipocyte size, a common measure of cetacean adiposity, and blubber thickness in beluga whales (Delphinapterus leucas). We used mixed-effect generalized linear models to test how sex and blubber layer influenced this relationship. We found a significant positive relationship between adipocyte size and blubber thickness in male but not female beluga whales, suggesting sex-specific differences in fat storage or mobilization. Blubber thickness may be maintained in female beluga whales during periods with low energy reserves, for example during gestation and lactation, to preserve buoyancy, insulation, and hydrodynamism, which may be especially important when supporting swimming calves. Continuing to develop methods to assess beluga whale health will further our understanding of the impact of current and future stressors on beluga whale populations.