Increased blubber cortisol in ice-entrapped beluga whales (Delphinapterus leucas)

Entrapments of whales in sea ice occur occasionally in the Arctic and often last several weeks or months, resulting in emaciation or death of whales. These events provide a unique opportunity for investigating the physiological response to a prolonged or chronic stress in an otherwise healthy population of marine mammals. By measuring cortisol in blubber, a peripheral tissue, we expect to see a reflection of long-term or chronic stress rather than short-term or acute stress. Adipose tissue should be less subject to rapid changes compared to blood cortisol, reflecting stressors experienced over a longer period of time, and should not be affected by potential stress associated with sampling. We measured blubber cortisol of 29 beluga whales (Delphinapterus leucas) entrapped in November 2006 in Husky Lakes basin and 26 whales from the same population (Eastern Beaufort Sea) during regular seasonal harvests in July of 2006 and 2007. Mean cortisol concentrations (+/- SEM) were seven times higher in blubber from entrapped whales (1.76 +/- 0.32 ng/g wet weight) compared to whales from regular seasonal harvests (0.26 +/- 0.042 ng/g wet weight) and appeared to increase with whale age. Our results provide a measure of blubber cortisol from a prolonged stress and demonstrate blubber cortisol as a useful indicator of longer-term exposure to stress in beluga whales.