Identifying factors that influence animal population density can provide insight into why it varies spatially and temporally and when a recovering population has reached an equilibrium density because of food resources (i.e., carrying capacity K). Although food availability is widely recognized as an important extrinsic factor limiting sea otter (Enhydra lutris) population density, can we determine when a population has reached K based on population size and prey availability? The goal of this study was to estimate K for Simpson Bay, Alaska by measuring the abundance of edible bivalves, the primary prey for sea otters for over 40 years. We then compared prey abundance and estimated replacement rate (i.e., the mean age of bivalves predated by sea otters) to estimated annual prey consumption based on the mean population density for the past 18 years. On average, 110 adult sea otters (5.2 km⁻²) have occupied Simpson Bay annually since 2001 consuming an estimated 176,660 kg of bivalves. The total biomass (standing stock) of the major bivalves (predominately butter clams and stained macomas) was 785,730 kg, so adult sea otters consumed about 22% annually. Given the stable abundance of sea otters over the past 18 years and evidence of sustainable prey replacement, sea otters in Simpson Bay appear to be at K. Understanding which factors regulate population density may be one of the most challenging ecological questions and require long-term monitoring for complete resolution. We suggest that studies such as this, when applied to a variety of littoral habitats occupied by sea otters, complement approaches that use proxies for prey availability to assess K. Future research should focus on a few sites, which are representative of the variety of littoral habitats occupied by sea otters around the North Pacific Rim. From those sites, we may learn how the balance among intrinsic and extrinsic factors affects regional sea otter population density. In addition, this approach provides a mechanistic assessment of K, which will better inform probabilistic inferences for sea otter population trends and help resource managers anticipate potential conflicts and tailor management strategies to benefit a wide range of recovering predators, such as the sea otter.

确定影响动物种群密度的因素可以深入了解为什么它会在空间和时间上发生变化，以及恢复种群何时因食物资源（即承载能力K）而达到平衡密度。尽管食物供应被广泛认为是限制海獭 ( Enhydra lutris ) 种群密度的重要外在因素，但我们能否根据种群规模和猎物供应情况确定种群何时达到K ？本研究的目的是估计K通过测量可食用双壳类动物（40 多年来一直是海獭的主要猎物）的丰度，为阿拉斯加州的辛普森湾（Simpson Bay）进行了调查。然后，我们根据过去 18 年的平均种群密度，将猎物丰度和估计的替代率（即海獭早于双壳类动物的平均年龄）与估计的年度猎物消耗量进行了比较。平均而言，自 2001 年以来，每年有110 只成年海獭（5.2 公里^-2）占据辛普森湾，估计消耗了 176,660 公斤双壳类动物。主要双壳类动物（主要是奶油蛤和染色巨蛤）的总生物量（常备库存）为 785,730 公斤，因此成年海獭每年消耗约 22%。鉴于过去 18 年海獭数量稳定，并且有可持续的猎物替代证据，辛普森湾的海獭似乎处于K. 了解哪些因素调节人口密度可能是最具挑战性的生态问题之一，需要长期监测才能完全解决。我们建议像这样的研究，当应用于海獭占据的各种沿海栖息地时，可以补充使用替代猎物可用性来评估K 的方法。未来的研究应集中在几个地点，这些地点代表了北太平洋沿岸海獭所占据的各种沿海栖息地。从这些地点，我们可以了解内在和外在因素之间的平衡如何影响区域海獭种群密度。此外，这种方法提供了K的机械评估，这将更好地为海獭种群趋势的概率推断提供信息，并帮助资源管理人员预测潜在的冲突并制定管理策略，使范围广泛的恢复捕食者受益，例如海獭。