Data from: Alaskan brown bears (Ursus arctos) aggregate and display fidelity to foraging neighborhoods while preying on Pacific salmon along small streams

The interaction between brown bears (Ursus arctos) and Pacific salmon (Oncorhynchus spp.) is important to the population dynamics of both species and a celebrated example of consumer-mediated nutrient transport. Yet, much of the site-specific information we have about the bears in this relationship comes from observations at a few highly visible but unrepresentative locations and a small number of radio-telemetry studies. Consequently, our understanding of brown bear abundance and behavior at more cryptic locations where they commonly feed on salmon, including small spawning streams, remains limited. We employed a non-invasive genetic approach (barbed wire hair snares) over four summers (2012-2015) to document patterns of brown bear abundance and movement among six spawning streams for sockeye salmon, O. nerka, in southwestern Alaska. The streams were grouped into two trios on opposite sides of Lake Aleknagik. Thus, we predicted that most bears would forage within only one trio during the spawning season because of the energetic costs associated with swimming between them or traveling around the lake, and show fidelity to particular trios across years because of the benefits of familiarity with local salmon dynamics and stream characteristics. Huggins closed-capture models based on encounter histories from genotyped hair samples revealed that as many as 41 individuals visited single streams during the annual six-week sampling season. Bears also moved freely among trios of streams but rarely moved between these putative foraging neighborhoods, either during or between years. By implication, even small salmon spawning streams can serve as important resources for brown bears, and consistent use of stream neighborhoods by certain bears may play an important role in spatially structuring coastal bear populations. Our findings also underscore the efficacy of non-invasive hair snagging and genetic analysis for examining bear abundance and movements at relatively fine spatial and temporal scales.

棕熊（Ursus arctos）与太平洋鲑属（Oncorhynchus spp.）的种间互动，对二者的种群动态均具有关键意义，同时也是消费者介导养分运输的经典研究范例。然而，目前学界对该共生关系中棕熊的相关认知，大多仅来自少数高可见性但缺乏代表性的观测点位，以及少量无线电遥测研究。因此，对于棕熊在更多隐匿生境——包括小型产卵溪流——中以鲑鱼为食的种群丰度与行为模式，我们的了解仍十分有限。本研究于2012至2015年的四个夏季，采用非侵入性遗传采样方法（带刺铁丝毛发诱捕器），在阿拉斯加西南部的6条红大麻哈鱼（O. nerka）产卵溪流中，记录棕熊的种群丰度与溪流间移动模式。这些溪流被划分为两组，每组各3条，分别坐落于阿莱纳吉克湖（Lake Aleknagik）的两岸。据此我们提出研究假设：由于在两组溪流间游动或绕行湖泊会产生高昂的能量成本，多数棕熊会在鲑鱼产卵季仅在其中一组溪流觅食；且由于熟悉当地鲑鱼种群动态与溪流特征可带来生存优势，棕熊会在不同年份间忠实使用同一组溪流。基于基因分型毛发样本的捕获历史数据构建的Huggins闭群捕获模型结果显示：在每年为期6周的采样季内，单条溪流最多可吸引41头棕熊到访。同时，棕熊可在同一组的多条溪流间自由移动，但极少在两组推定的觅食片区之间穿梭，无论在同一年度还是不同年份间均是如此。这一研究结果表明，即便小型鲑鱼产卵溪流也可成为棕熊的重要觅食资源；而部分棕熊持续使用特定溪流组的行为，可能在空间结构上塑造了沿海棕熊种群。此外，本研究也凸显了非侵入性毛发采样与遗传分析方法，在相对精细的时空尺度下研究棕熊种群丰度与移动模式的有效性。