Assessing longitudinal patterns of reproduction and stress of humpback whales (Megaptera novaeangliae) via a novel analytical technique using baleen

Understanding the physiology of baleen whales is critical for their effective management and conservation but sampling free-living whales is exceedingly difficult. To overcome this issue, baleen was used to analyze hormone and mercury patterns, allowing for multi-year retrospective investigation into stress and reproductive physiology in humpback whales. Progesterone, an important reproductive hormone, showed an increase during periods of known pregnancy as confirmed by sighting data and strengthens the hypothesis that baleen can be used to determine pregnancy rates in humpback whales. Two glucocorticoids involved in metabolism and stress, cortisol and corticosterone, did not increase during pregnancy as seen in other mysticete species and highlights the need for additional studies into pregnancy physiology in baleen whales. Estradiol and testosterone, hormones involved in reproduction, did not show patterns of increase or decrease in females during period of known gestation or parturition. Analysis of cortisol and corticosterone patterns between whales with different fatality causes (ship strike, illness, or entanglement) showed discrepancies in glucocorticoid patterns depending on how the whale died. The whales that were fatally struck by ships had relatively low and stable glucocorticoid concentrations while a frequently entangled whale had exceptionally high corticosterone concentrations throughout the baleen. A chronically ill whale had concurrent increases in both hormones over the baleen plate until approximately six months before death when both hormones fell to very low levels. These results show that baleen analysis can be a useful tool to determine causes of death in both historical and present-day baleen plates. Mercury concentrations along the baleen plates revealed that individual prey preferences might influence baleen mercury levels more than sex or pregnancy. The female had 2-3 times higher mercury concentrations than the two males and levels peaked during the first half of lactation. The two males had similar values even though they were 31 years apart in age. Analysis of baleen allowed for a multi-year retrospective approach to determine glucocorticoid, progesterone, and mercury patterns during pregnancy and with varying causes of death in a hard to sample species. Further use of this method could result in increased understanding of baleen whale physiology during various life history events