Alaska Science Center, U.S. Geological Survey, Anchorage, AK, USA.
Polar Science Center, University of Washington, Seattle, WA, USA.
Glob Chang Biol. 2021 Jun;27(12):2684-2701. doi: 10.1111/gcb.15572. Epub 2021 Mar 12.
Polar bears (Ursus maritimus) are experiencing loss of sea ice habitats used to access their marine mammal prey. Simultaneously, ocean warming is changing ecosystems that support marine mammal populations. The interactive effects of sea ice and prey are not well understood yet may explain spatial-temporal variation in the response of polar bears to sea ice loss. Here, we examined the potential combined effects of sea ice, seal body condition, and atmospheric circulation patterns on the body condition, recruitment, diet, and feeding probability of 469 polar bears captured in the Chukchi Sea, 2008-2017. The body condition of ringed seals (Pusa hispida), the primary prey of females and subadults, was related to dietary proportions of ringed seal, feeding probability, and the body condition of females and cubs. In contrast, adult males consumed more bearded seals (Erignathus barbatus) and exhibited better condition when bearded seal body condition was higher. The litter size, number of yearlings per adult female, and the condition of dependent young were higher following winters characterized by low Arctic Oscillation conditions, consistent with a growing number of studies. Body condition, recruitment, and feeding probability were either not associated or negatively associated with sea ice conditions, suggesting that, unlike some subpopulations, Chukchi Sea bears are not currently limited by sea ice availability. However, spring sea ice cover declined 2% per year during our study reaching levels not previously observed in the satellite record and resulting in the loss of polar bear hunting and seal pupping habitat. Our study suggests that the status of ice seal populations is likely an important factor that can either compound or mitigate the response of polar bears to sea ice loss over the short term. In the long term, neither polar bears nor their prey are likely robust to limitless loss of their sea ice habitat.
北极熊（Ursus maritimus）正在失去用于获取海洋哺乳动物猎物的海冰栖息地。与此同时，海洋变暖正在改变支持海洋哺乳动物种群的生态系统。海冰和猎物的相互作用尚不清楚，但可能解释了北极熊对海冰减少的反应在时空上的变化。在这里，我们研究了海冰、海豹身体状况和大气环流模式对 2008-2017 年在楚科奇海捕获的 469 只北极熊的身体状况、繁殖、饮食和觅食概率的潜在综合影响。环斑海豹（Pusa hispida）的身体状况是雌性和亚成体的主要猎物，与环斑海豹的饮食比例、觅食概率以及雌性和幼崽的身体状况有关。相比之下，成年雄性消耗更多的髯海豹（Erignathus barbatus），并且当髯海豹的身体状况较好时，它们的状况也更好。每只成年雌熊的幼崽数量、成年雌熊的幼熊数量和幼崽的状况在北极涛动条件较低的冬季更高，这与越来越多的研究结果一致。身体状况、繁殖和觅食概率与海冰条件要么没有关系，要么呈负相关，这表明与一些亚种群不同，楚科奇海的熊目前不受海冰可利用性的限制。然而，在我们的研究期间，春季海冰覆盖面积每年减少 2%，达到了卫星记录中以前从未观察到的水平，导致北极熊狩猎和海豹产仔的栖息地丧失。我们的研究表明，冰海豹种群的状况可能是一个重要因素，短期内可能会加剧或减轻北极熊对海冰减少的反应。从长远来看，北极熊及其猎物都不太可能对其海冰栖息地的无限丧失有很强的适应能力。
