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Causes and Extent of Natural Mortality Among Steller Sea Lion (Eumetopias jubatus) Pups
Abstract: The authors studied the causes and extent of mortality in endangered Steller sea lion (Eumetopias jubatus) pups at a small rookery in the northern Gulf of Alaska over seven consecutive summers (2001 to 2007). Mortality among pups up to 2.5 mo post-partum (n = 69) averaged 15.4% (range = 3.8 to 27.8%) and was not dependent on number of pups born. The causes of mortalities varied greatly from year to year, although high surf conditions and killer whale predation accounted for more than half of all deaths. Stillbirths, traumatic injury, and maternal abandonment were individually relatively minor sources of mortality. Causes of mortality were age-dependent. Pups greater than 2 wks old were not washed away by high surf conditions or killed by traumatic injury; whereas pups less than 1 mo old were not subject to predation. The authors also summarize historical observations of pup mortality in this species to compare similarities over time and differences between regions. Current and historic evidence suggests that rates of pup mortality have been higher in the eastern/increasing population of Steller sea lions compared to the western/decreasing population. Therefore, an increase in pup mortality was probably not a major cause of the overall population decline or current lack of recovery.
Key Words: Steller sea lion, Eumetopias jubatus, abandonment, pup mortality, high surf, predation, stillbirths, traumatic injury
Document Type: Research article
Page Numbers: 277-287