Validating Potential Dilution Markers to Standardize Cortisol in Beluga Whale ( <scp> <i>Delphinapterus leucas</i> </scp> ) Blow

ABSTRACT There has been increasing interest in blow sampling for monitoring multiple aspects of cetacean biology and physiology. Yet some limitations remain, including the lack of a fully validated dilution marker for the standardization of hormone concentrations to account for variation in water vapor and environmental water content of breaths. This study investigated both urea and total protein as potential dilution markers in beluga whale blow utilizing trained aquarium belugas. Samples were obtained in conjunction with paired blood samples during monthly clinical draws, in the morning and afternoon, and during opportunistic biological challenge events for physiological validation. Despite previous studies' success with urea in large whales, neither urea nor total protein demonstrated consistent results, nor a clear advantage over the other. In addition, some evidence that a dilution marker may not be necessary within aquaria was noted, and conditions of blow collection within aquaria vs. the field are important considerations for study design and data interpretation.