Male baleen whales have long been suspected to have annual cycles in testosterone, but due to diﬃculty in collecting endocrine samples, little direct evidence exists to conﬁrm this hypothesis. Potential inﬂuences of stress or adrenal stress hormones (cortisol, corticosterone) on male reproduction have also been diﬃcult to study. Baleen has recently been shown to accumulate steroid hormones during growth, such that a single baleen plate contains a continuous, multi-year retrospective record of the whale's endocrine history. As a preliminary investigation into potential testosterone cyclicity in male whales and inﬂuences of stress, we determined patterns in immunoreactive testosterone, two glucocorticoids (cortisol and corticosterone), and stable-isotope (SI) ratios, across the full length of baleen plates from a bowhead whale (Balaena mysticetus), a North Atlantic right whale (Eubalaena glacialis) and a blue whale (Balaenoptera musculus), all adult males. Baleen was subsampled at 2 cm (bowhead, right) or 1 cm (blue) intervals and hormones were extracted from baleen powder with methanol, followed by quantiﬁcation of all three hormones using enzyme immunoassays validated for baleen extract of these species. Baleen of all three males contained regularly spaced peaks in testosterone content, with number and spacing of testosterone peaks corresponding well to SI data and to species-speciﬁc estimates of annual baleen growth rate. Cortisol and corticosterone exhibited some peaks that co-occurred with testosterone peaks, while other glucocorticoid peaks occurred independent of testosterone peaks. The right whale had unusually high glucocorticoids during a period with a known entanglement in ﬁshing gear and a possible disease episode; in the subsequent year, testosterone was unusually low. Further study of baleen testosterone patterns in male whales could help clarify conservation- and management-related questions such as age of sexual maturity, location and season of breeding, and the potential eﬀect of anthropogenic and natural stressors on male testosterone cycles.
- Marine mammals
ASJC Scopus subject areas
- Ecological Modeling
- Nature and Landscape Conservation
- Management, Monitoring, Policy and Law