Blubber cortisol levels in humpback whales (Megaptera novaeangliae): a measure of physiological stress without effects from sampling

• Published in: General and Comparative Endocrinology
• Main Authors: Mingramm, Fletcher M. J., Keeley, Tamara, Whitworth, Deanne J., Dunlop, Rebecca A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Academic Press 2020
• Subjects: Humpback whale; blubber; cortisol; stress; validation; 1103 Animal Science and Zoology; 1310 Endocrinology; baleen whales; Humpback Whale; Megaptera novaeangliae
• Online Access: https://espace.library.uq.edu.au/view/UQ:8bba468

Baleen whales are vulnerable to environmental impacts due to low fecundity, capital breeding strategies, and their reliance on a large amount of prey resources over large spatial scales. There has been growing interest in monitoring health and physiological stress in these species but, to date, few measures have been validated. The purpose of this study was to examine whether blubber cortisol could be used as a measure of physiological stress in humpback whales. Cortisol concentrations were initially compared between live, presumably 'healthy' whales (n = 187) and deceased whales (n = 35), which had died after stranding or entanglement, or washed ashore as a carcass. Deceased whales were found to have significantly higher cortisol levels (mean ± SD; 5.47 ± 4.52 ng/g) than live whales (0.51 ± 0.14 ng/g; p < 0.001), particularly for those animals that had experienced prolonged trauma (e.g. stranding) prior to death. Blubber cortisol levels in live whales were then examined for evidence of life history-related, seasonal, or sampling-related effects. Life history group and sampling-related factors, such as encounter time and the number of biopsy sampling attempts per animal, were found to be poor predictors of blubber cortisol levels in live whales. In contrast, blubber cortisol levels varied seasonally, with whales migrating north towards the breeding grounds in winter having significantly higher levels (0.54 ± 0.21 ng/g, p = 0.016) than those migrating south towards the feeding grounds in spring (0.48 ± 1.23 ng/g). These differences could be due to additional socio-physiological stress experienced by whales during peaks in breeding activity. Overall, blubber cortisol appears to be a suitable measure of chronic physiological stress in humpback whales.