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.
