Baleen whales are distributed throughout the world’s oceans and are therefore subject to myriad anthropogenic stressors, but understanding how these stressors effect physiology is difficult. One insight into the stress response is measurement of glucocorticoids; glucocorticoids are steroid hormones involved in many metabolic and inflammatory responses to changes in both external and internal environments. Here, we investigate how fatal entanglement, ship strike, and natural illness affected production of two glucocorticoid steroid hormones—cortisol and corticosterone—over multiple years by extracting hormones from baleen plates of four humpback whales (Megaptera novaeangliae). We hypothesized that cortisol and corticosterone would vary according to the stressor involved, with an entangled whale showing greater spikes in glucocorticoids than whales that died immediately from ship strike. Whales that died of natural illness should have increasing glucocorticoids as the illness progresses. To test glucocorticoid secretion patterns, we used baleen from a total of four whales, two males and two females, and assayed for cortisol and corticosterone using enzyme immunoassay.
Results/Conclusions
The entangled whale had average cortisol levels up to thirty times higher than the other whales (14.24 vs 0.46-1.62 pg g-1 baleen); corticosterone levels were up to 1.8 times higher than the other whales that did not experience entanglement (4.96 vs 2.77-4.47 pg g-1). A 66-year-old male who died from a natural illness showed a slow increase in both cortisol and corticosterone followed by a sharp decline in both glucocorticoids before death. The correlation between cortisol and corticosterone varied considerably between the four whales; r-squared values were 0.007 and 0.380 for the ship struck whales, -0.583 for the entangled whale, and 0.900 for the chronically ill whale. All but one whale, the 45-year-old ship strike female, had significant correlations. This study shows cortisol and corticosterone vary with cause of death and can be a useful tool in determining physiological changes in humpback whales from different stressor types.