ABSTRACT: Anthropogenic noise is increasingly recognized as a potentially significant stressor for marine animals. Beaked whales, deep-diving cephalopod predators, have been disproportionally present in atypical mass stranding events coincident with military sonar exercises, while frequently disturbed populations that do not strand may have reductions in fitness. We present in situ measures of prey availability, a key factor affecting fitness, for 2 distinct populations of Mesoplodon densirostris: one on a US Navy range in The Bahamas and one nearby in an area less exposed to sonar. The variables most strongly correlated with beaked whale habitat use were related to the distribution of deep-sea squid (mode spacing, peak depth, and 100 m scale variability). All squid metrics were more favorable for beaked whales at the less exposed site than those on the range. To develop a generalized functional relationship between prey resources and beaked whale habitat use, data from The Bahamas were combined with comparable data from another Navy range and the larger beaked whale, Ziphius cavirostris. A power-law relationship was observed between a normalized metric of prey quality and whale habitat use. A critical threshold in prey characteristics, below which beaked whales appear unlikely to be successful, but above which small changes in resource availability enable large gains for predators, was observed. This implies that modest changes in the behavior of individual whales associated with disturbance can have consequential population effects. Our results elucidate the ecological realities of these elusive and sensitive beaked whales, and the importance of environmental context in effective spatial planning for the deep sea.

中文翻译：

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在喙鲸与其猎物之间的功能关系中确定的临界阈值

摘要：人为噪声日益被认为是海洋动物潜在的重要压力源。在与军事声纳练习同时发生的非典型大规模搁浅事件中，不成比例地存在着喙鲸，头足类捕食者的深潜，而经常不打扰的不安定种群可能会降低其适应度。我们提出了猎物可用性的原位测量，这是影响适合度的两个不同种群的中观种群的猎物的关键因素：一架在巴哈马的美国海军靶场上，另一架在声呐较少的地区附近。与喙鲸栖息地使用最相关的变量与深海鱿鱼的分布有关（模式间隔，峰深和100 m尺度变化）。所有鱿鱼指标都比暴露范围内的位置更适合暴露程度较低的地点的喙鲸。为了建立猎物资源与喙鲸栖息地使用之间的一般功能关系，将巴哈马群岛的数据与另一海军范围和较大的喙鲸Ziphius cavirostris的可比数据相结合。在捕食质量的标准化度量与鲸鱼栖息地使用之间观察到幂律关系。观察到一个捕食特性的临界阈值，低于此阈值的喙鲸似乎不太可能成功，但高于此阈值时，资源可用性的微小变化可使捕食者获得较大收益。这意味着与干扰有关的个别鲸鱼行为的适度变化可能会产生相应的种群效应。我们的研究结果阐明了这些难以捉摸和敏感的喙鲸的生态现实，以及环境背景在深海有效空间规划中的重要性。