Recent increases in survival of western Steller sea lions in Alaska and implications for recovery

[摘要] ABSTRACT: Survival rates of endangered western stock Steller sea lions Eumetopias jubatus east of Samalga Pass (~170°W) have rebounded to nearly the same levels estimated for the 1970s prior to their decline in abundance. We estimated survival of sea lions hot-branded as pups (N = 1449) in 2000-2005 using Cormack-Jolly-Seber mark-recapture models and sighting data collected through 2011. Survivorship to Age 7 yr was greater for females (range: 0.352-0.386) than males (0.228-0.275), but was similar for each sex across the study area. Survival was lowest in the first year and increased through Age 4+ yr for both sexes in the eastern Gulf of Alaska (144-150°W). However, to the west, first-year survivorship was greater or equal to that of Year 2, and the difference was generally greater for males than females. Regional differences in the pattern of early survival could reflect spatial variability in early life history (e.g. duration of maternal care, growth rate) or habitat characteristics (e.g. prey availability, rates of predation). Population models indicate that natality of the increasing population east of Samalga Pass in 2000-2012 may not be significantly different from rates estimated for the 1970s prior to the decline in overall western abundance. Given current information, western Steller sea lions may satisfy the stock-wide demographic down-listing (to threatened status) criterion by 2015. However, due to continued abundance declines west of Samalga Pass, where no survival data are currently available, it is less certain that the western stock’s regional down-listing criteria will be achieved.

[学科分类] 动物科学

[关键词] Steller sea lion;Alaska;Branding;Survival