Abstract

Sea otters (Enhydra lutris) once ranged throughout the coastal regions of the north Pacific. They were extirpated over much of their range due to extensive hunting associated with the fur trade of the 18th and 19th centuries resulting in widespread population reduction and fragmentation until eventual protection in 1911 by international treaty. All extant sea otter populations are thought to have relatively low genetic variation as a result of fur trade exploitation. Populations that experience severe population reduction and associated inbreeding may also suffer from a general reduction in fitness termed inbreeding depression. This includes a decrease in the male reproductive hormone, testosterone, and an increase in the stress related hormones, cortisol and corticosterone. Here we investigate whether testosterone and cortisol or corticosterone are correlated with genetic diversity as an index of inbreeding depression in sea otter populations. Corticosterone, but not cortisol and testosterone, was significantly negatively correlated with genetic diversity in both males (r=0.90) and females (r=0.94). A significant correlation between these variables does not prove sea otter populations are experiencing inbreeding depression. However, the strength of these correlations suggests that inbreeding depression may be a concern within sea otter populations with the lowest genetic variability. Future monitoring of inbreeding indices may be needed to determine long-term sea otter population viability.