Seasonal reproductive endocrinology and anatomy of Steller sea lions (Eumetopia jubatus)

Abstract

The decline of western Alaskan Steller sea lions (SSLs) may be related to changes in reproductive rates. However, our understanding of SSL reproductive biology is poor. My objectives were to determine if saliva samples are a valid alternative to plasma samples for measurements of peripheral progesterone and testosterone, to describe annual cycles of steroid concentrations, and to provide anatomical verification of reproductive endocrinology. Samples were collected from adult, captive and wild SSLs. Progesterone and testosterone concentrations in paired plasma and saliva samples were highly correlated (96% and 84%, respectively). Captive SSLs had seasonal variations in these steroids that did not follow typical pinniped patterns, suggesting that reproductive activity may be sensitive to social cues. The wwild SSLs exhibited steroid patterns similar to other seasonal breeders. Vaginal cytology could not be evaluated for detecting estrus because no samples were obtained during estrus. Testes volume was correlated to plasma testosterone concentrations (71%).