Reproductive Ability of Elderly Male Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in Captivity

The present study, the first to examine breeding ability in elderly cetaceans, addressed the reproductive capacity of four captive male Indo-Pacific bottlenose dolphins that are among the oldest in the world (47-50 years in 2017). The dolphins' reproductive ability was assessed by monthly monitoring of serum testosterone (T) levels over nine years (2009-2017), and examination of semen characteristics. Serum T concentrations from blood samples were measured by fluorescence immunoassay. The dolphins showed regular peaks in their serum T levels every year or once every few years. The mean monthly T level showed a significant seasonal change, beginning to elevate in January, peaking from March to May, and then declining until September. Semen production was confirmed in three of the four individuals, and semen quality was confirmed for those dolphins through collections one or two times a month for a year. The sperm concentration in samples from those individuals was comparatively high. These data indicated that the dolphins had the capacity to breed every year. Indo-Pacific bottlenose dolphins are capable of surviving to older ages in captivity than they typically reach in the wild, and it is likely that even elderly individuals retain their breeding ability.