Data from: Natal and breeding philopatry of female Steller sea lions in southeastern Alaska

Information on drivers of dispersal is critical for wildlife conservation but is rare for long-lived marine mammal species with large geographic ranges. We fit multi-state mark-recapture models to resighting data of 369 known-aged Steller sea lion (Eumetopias jubatus) females marked as pups on their natal rookeries in southeastern Alaska from 1994-2005 and monitored from 2001-15. We estimated probabilities of females being first observed parous at their natal site (natal philopatry), and of not moving breeding sites among years (breeding philopatry) at large (> 400 km, all five rookeries in southeastern Alaska) and small (< 4 km, all islands within the largest rookery, Forrester Island Complex, F) spatial scales. At the rookery scale, natal philopatry was moderately high (0.776-0.859) for most rookeries and breeding philopatry was nearly 1, with < 3% of females switching breeding rookeries between years. At more populous islands at F, natal philopatry was 0.500-0.684 versus 0.295-0.437 at less populous islands, and breeding philopatry was 0.919-0.926 versus 0.604-0.858. At both spatial scales, the probability of pupping at a non-natal site increased with population size of, and declined with distance from, the destination site. Natal philopatry of < 1 would increase gene flow, improve population resilience, and promote population recovery after decline in a heterogeneous environment. Very high breeding philopatry suggests that familiarity with neighboring females and knowledge of the breeding site (the topography of pupping sites and nearby foraging locations) may be a critical component to reproductive strategies of sea lions.

明确扩散驱动因素的相关信息对于野生动物保护至关重要，但对于地理分布范围广阔的长寿海洋哺乳动物类群而言，此类数据却极为匮乏。本研究针对1994-2005年间在阿拉斯加东南部出生繁殖地标记为幼崽的369头已知年龄的雌性北海狮（Steller sea lion, Eumetopias jubatus）的重目击数据，构建了多状态标记重捕模型（multi-state mark-recapture models），并于2001-2015年对其开展监测。我们分别在大空间尺度（>400km，涵盖阿拉斯加东南部全部5个繁殖群）与小空间尺度（<4km，涵盖最大繁殖群福里斯特岛群（Forrester Island Complex, F）内的所有岛屿）下，估算了雌性个体首次在出生地繁殖地产仔的概率（出生地繁殖保真度，natal philopatry），以及年度间不更换繁殖地的概率（繁殖地保真度，breeding philopatry）。在繁殖群尺度下，多数繁殖群的出生地繁殖保真度处于中等偏高水平（0.776~0.859）；繁殖地保真度近乎为1，年度间更换繁殖群的雌性个体占比不足3%。在福里斯特岛群内，种群规模更大的岛屿上，出生地繁殖保真度为0.500~0.684，而种群规模更小的岛屿上该值为0.295~0.437；对应的繁殖地保真度则分别为0.919~0.926与0.604~0.858。在两种空间尺度下，雌性个体在非出生地繁殖地产仔的概率均随目标繁殖地的种群规模增大而升高，随与该目标地的距离增加而降低。当出生地繁殖保真度小于1时，可提升基因交流水平、增强种群恢复力，并在异质环境中助力衰退种群实现复育。极高的繁殖地保真度表明，对邻近雌性的熟悉程度以及对繁殖地（产仔位点地形与周边觅食区域的认知）或许是海狮繁殖策略的关键组成部分。