We describe a method to allow acoustic sampling at depths not reachable by the higher frequencies of ship hull-mounted echosounders and observe the abundance and behaviour of individual organisms in front of trawls. A self-contained scientific echosounder with a 120 kHz transducer was mounted forward-facing on the headline of a macrozooplankton trawl that was obliquely towed from 0 to 1000 m depth, to investigate the mesopelagic fauna. With the use of a forward-facing echosounder, we were able to estimate organism densities in front of the trawl, the vertical profiles of organism target strength and the movement of organisms in front of the trawl. We demonstrate that a forward-facing trawl-mounted echosounder is a simple and useful method to investigate the distribution of mesopelagic fauna at depth.

我们描述了一种方法，该方法允许在船体安装的回波探测器的较高频率无法到达的深度进行声学采样，并观察拖网渔船前单个生物的丰度和行为。将带有120 kHz换能器的独立科学回声探测器面向前方安装在巨藻浮游生物拖网的标题上，该拖网从0到1000 m的深度倾斜拖曳，以研究中古生代动物。通过使用向前的回声测深仪，我们能够估算拖网前的生物密度，目标生物强度的垂直剖面以及拖网前的生物运动。我们证明了向前拖网式安装回声测深仪是一种简单而有用的方法，可以用来研究中层近生动物的深度分布。