Polar bears (Ursus maritimus) rely on annual sea ice as their primary habitat for hunting marine mammal prey. Given their long lifespan, wide geographic distribution, and position at the top of the Arctic marine food web, the diet composition of polar bears can provide insights into temporal and spatial ecosystem dynamics related to climate-mediated sea ice loss. Polar bears with the greatest ecological constraints on diet composition may be most vulnerable to climate-related changes in ice conditions and prey availability. We used quantitative fatty acid signature analysis (QFASA) to estimate the diets of polar bears (n = 419) in two western Canadian Arctic subpopulations (Northern Beaufort Sea and Southern Beaufort Sea) from 1999 to 2015. Polar bear diets were dominated by ringed seal (Pusa hispida), with interannual, seasonal, age- and sex-specific variation. Foraging area and sea ice conditions also affected polar bear diet composition. Most variation in bear diet was explained by longitude, reflecting spatial variation in prey availability. Sea ice conditions (extent, thickness, and seasonal duration) declined throughout the study period, and date of sea ice break-up in the preceding spring was positively correlated with female body condition and consumption of beluga whale (Delphinapterus leucas), suggesting that bears foraged on beluga whales during entrapment events. Female body condition was positively correlated with ringed seal consumption, and negatively correlated with bearded seal consumption. This study provides insights into the complex relationships between declining sea ice habitat and the diet composition and foraging success of a wide-ranging apex predator.

北极熊（Ursus maritimus）依靠每年的海冰作为狩猎海洋哺乳动物猎物的主要栖息地。鉴于北极熊的寿命长，地理分布广泛且位于北极海洋食物网的顶部，因此其饮食成分可以提供与气候介导的海冰流失有关的时空生态系统动态的见解。对饮食组成具有最大生态限制的北极熊可能最容易受到与气候有关的冰况和猎物供应变化的影响。我们使用了定量脂肪酸特征分析（QFASA）来估算北极熊的饮食（n 1999年至2015年，在加拿大西部的两个北极小种群（北博福特海和南博福特海）中找到了419）。北极圈圈海豹（Pusa hispida）主导了北极熊的饮食，并具有年际，季节，年龄和性别差异。觅食区和海冰条件也影响了北极熊的饮食组成。熊饮食的大多数变化是由经度解释的，反映了猎物可利用性的空间变化。在整个研究期间，海冰状况（程度，厚度和季节性持续时间）均下降，并且前一个春季海冰破裂的日期与女性身体状况和白鲸的消费量正相关（Delphinapterus leucas），表明在诱捕事件中在白鲸中觅食了熊。女性身体状况与环海豹食用呈正相关，与海豹海豹食用呈负相关。这项研究提供了有关海冰栖息地减少与饮食组成以及广泛的先天捕食者觅食成功之间复杂关系的见解。