National Institute of Polar Research, 190-8518 Tachikawa, Tokyo, Japan;
Department of Polar Science, The Graduate University for Advanced Studies, SOKENDAI, 190-8518 Tachikawa, Tokyo, Japan.
Proc Natl Acad Sci U S A. 2020 Dec 8;117(49):31242-31248. doi: 10.1073/pnas.2014021117. Epub 2020 Nov 16.
Understanding what, how, and how often apex predators hunt is important due to their disproportionately large effects on ecosystems. In Lake Baikal with rich endemic fauna, Baikal seals appear to eat, in addition to fishes, a tiny (<0.1 g) endemic amphipod (the world's only freshwater planktonic species). Yet, its importance as prey to seals is unclear. Globally, amphipods are rarely targeted by single-prey feeding (i.e., nonfilter-feeding) mammals, presumably due to their small size. If is energetically important prey, Baikal seals would exhibit exceptionally high foraging rates, potentially with behavioral and morphological specializations. Here, we used animal-borne accelerometers and video cameras to record Baikal seal foraging behavior. Unlike the prevailing view that they predominantly eat fishes, they also hunted at the highest rates (mean, 57 individuals per dive) ever recorded for single-prey feeding aquatic mammals, leading to thousands of catches per day. These rates were achieved by gradual changes in dive depth following the diel vertical migration of swarms. Examining museum specimens revealed that Baikal seals have the most specialized comb-like postcanine teeth in the subfamily Phocinae, allowing them to expel water while retaining prey during high-speed foraging. Our findings show unique mammal-amphipod interactions in an ancient lake, demonstrating that organisms even smaller than krill can be important prey for single-prey feeding aquatic mammals if the environment and predators' adaptations allow high foraging rates. Further, our finding that Baikal seals directly eat macroplankton may explain why they are so abundant in this ultraoligotrophic lake.
了解顶级捕食者的捕食方式、捕食对象和捕食频率非常重要，因为它们对生态系统的影响大得不成比例。在贝加尔湖，拥有丰富特有动物群的海豹，除了鱼类之外，似乎还会捕食一种体型极小（<0.1 克）的特有片脚类动物（这是世界上唯一的淡水浮游物种）。然而，其作为海豹猎物的重要性尚不清楚。在全球范围内，片脚类动物很少成为单一猎物（即非滤食性）哺乳动物的目标，这大概是因为它们体型较小。如果 是重要的能量来源，那么海豹的觅食率应该非常高，可能具有行为和形态上的专门化特征。在这里，我们使用动物携带的加速度计和摄像机来记录海豹的觅食行为。与普遍认为它们主要以鱼类为食的观点不同，它们还以最高的速率（每次潜水 57 只）捕食 ，这是有记录以来单一猎物觅食的水生哺乳动物中最高的，每天可捕获数千只。这些速率是通过随着 群体的昼夜垂直迁移而逐渐改变潜水深度来实现的。检查博物馆标本表明，贝加尔海豹具有在 Phocinae 亚科中最具专业化的梳状后齿，使它们能够在高速觅食时排出水并保留猎物。我们的研究结果表明，在古老的湖泊中存在独特的哺乳动物与片脚类动物的相互作用，表明即使比磷虾还小的生物，如果环境和捕食者的适应能力允许高觅食率，也可以成为单一猎物觅食的水生哺乳动物的重要猎物。此外，我们发现贝加尔海豹直接食用大型浮游动物，这可能解释了为什么它们在这个超寡营养湖中如此丰富。
