Many pelagic animals, such as krill, lanternfish, and cephalopods, migrate to deep water at dawn to avoid visual predators during daylight hours and move up toward the sea surface at dusk to search for food. This behavior is termed “diel vertical migration.” Migrating animals graze on phytoplankton or zooplankton and in turn serve as food for higher trophic levels, hence providing a key mechanism for carbon export via this migration. These animals are often observed as sound-scattering layers by echosounders, but the animals causing the acoustic scattering are difficult to identify using acoustics alone. In a spring 2019 experiment in Monterey Bay, we deployed autonomous underwater and surface vehicles over a seabed-mounted upward-looking echosounder to collect environmental DNA (eDNA) with the goal of identifying the vertically migrating animals. The echosounder was installed at 890-m depth on the Monterey Accelerated Research System (MARS) seabed cabled ocean observatory, providing real-time data of acoustic backscatter from the full water column. One long-range autonomous underwater vehicle (LRAUV) carrying a Third-Generation Environmental Sample Processor (3G-ESP) acquired water samples from a sequence of layers from near surface down to $\sim$ 290 m as directed by the distribution of animals observed by the echosounder. During the sampling of each layer, the LRAUV ran on a tight circular yo-yo trajectory directly above the echosounder, remaining in its beam by acoustically tracking a station-keeping Wave Glider on the sea surface marking the echosounder’s latitude and longitude. The persistent and simultaneous acoustic observation and eDNA acquisition enables identification of animals at precise locations to better understand their vertical migration behaviors. We present the methods and the system performance in the experiment.

中文翻译：

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自主水下航行器在海底测深仪波束内对垂直迁移生物层的持续采样

许多中上层动物，如磷虾、灯笼鱼和头足类动物，在黎明时分迁移到深水区，以避开白天的视觉捕食者，并在黄昏时上浮到海面寻找食物。这种行为被称为“直接垂直迁移”。迁徙动物以浮游植物或浮游动物为食，进而作为更高营养水平的食物，因此通过这种迁徙提供了碳输出的关键机制。这些动物经常被回声测深​​仪观察为声音散射层，但单独使用声学很难识别引起声学散射的动物。在 2019 年春季在蒙特利湾进行的一项实验中，我们在安装在海底的仰视测深仪上部署了自主水下和水面车辆，以收集环境 DNA (eDNA)，目的是识别垂直迁移的动物。测深仪安装在蒙特雷加速研究系统 (MARS) 海底电缆海洋观测站的 890 米深处，提供来自整个水体的声学反向散射的实时数据。一个携带第三代环境采样处理器 (3G-ESP) 的远程自主水下航行器 (LRAUV) 从近地表到 $\sim$ 290 m 的一系列层中采集水样，按照观察到的动物分布进行指示通过回声测深仪。在每一层的采样过程中，LRAUV 沿着回声测深仪正上方的紧密圆形溜溜球轨迹运行，通过声学跟踪海面上的定位波滑翔机来标记回声测深仪的纬度和经度，从而保持在其波束中。持续和同步的声学观察和 eDNA 采集能够在精确位置识别动物，以更好地了解它们的垂直迁移行为。我们在实验中介绍了方法和系统性能。