Assessing longitudinal profiles of glucocorticoid concentrations in the baleen of male and female southern right whales ( Eubalaena australis)

Abstract

Marine mammals are subject to a variety of anthropogenic and natural stressors. However, it is still poorly understood how these stressors may affect physiological adaptations including affecting reproductive biology. Due to the association between glucocorticoids and the general health and wellbeing of animals, the monitoring of stress responses in mammals which trigger the production of glucocorticoids has grown in popularity in conservation studies. In the 1950s, the southern right whale (Eubalaena australis, hereafter SRWs) was given legal protection against whaling after which populations gradually increased again. Long-term annual arial surveys along the South African calving ground have, however, uncovered some drastic changes in the demographics of the South African population of SRWs, including a reduced reproductive rate and overall reduced body condition. In this regard, it would be important to gain a better understanding on the physiological responses of these whales to stressors as to gain an insight in the biological consequences of increased pressures on their environment. Therefore, this study aimed to look at longitudinal glucocorticoid (bGC) profiles in baleen plates of male and female SRWs and assess the relationship with reproductive hormones (androgens (bA) and progestogens (bP) respectively). A biological validation established a corticosterone assay's appropriateness for quantifying bGC metabolites in SRW baleen. Further results indicated a strong correlation between bGC and bP concentrations in females. Males ii with low levels of bA and bGC, and only a few brief moments of heightened bGC raised the questions of male sexual maturity and how they may respond to mating behaviours. The results of this study contribute to the understanding of SRW physiological responses to stressors and will aid in further research on the effects of anthropogenic pressures on their environment.