Body condition impacts blood and muscle oxygen storage capacity of free-living beluga whales (Delphinapterus leucas)

Abstract

Arctic marine ecosystems are currently undergoing rapid environmental changes. Over the past 20 years, individual growth rates of beluga whales (Delphinapterus leucas) have declined, which may be a response to climate change; however, scarcity of physiological data makes it difficult to gauge the adaptive capacity and resilience of the species. We explored relationships between body condition and physiological parameters pertaining to oxygen (O2) storage capacity in 77 beluga whales in the eastern Beaufort Sea. Muscle myoglobin concentrations averaged 77.9 mg g−1, one of the highest values reported among mammals. Importantly, blood hematocrit, hemoglobin, and muscle myoglobin concentrations correlated positively to indices of body condition, including maximum half-girth to length ratios. Thus, a whale with the lowest body condition index would have ∼27% lower blood (26.0 vs. 35.7 mL kg−1) and 12% lower muscle (15.6 vs. 17.7 mL kg−1) O2 stores than a whale of equivalent mass with the highest body condition index; with the conservative assumption that underwater O2 consumption rates are unaffected by body condition, this equates to a >3 minute difference in maximal aerobic dive time between the two extremes (14.3 vs. 17.4 minutes). Consequently, environmental changes that negatively impact body condition may hinder the ability of whales to reach preferred prey sources, evade predators, and escape ice entrapments. The relationship between body condition and O2 storage capacity may represent a vicious cycle, in which environmental changes resulting in decreased body condition impair foraging, leading to further reductions in condition through diminished prey acquisition and/or increased foraging efforts.