Multispecies schools of small planktivorous fishes are important constituents of reefs and coastal infrastructure; however, determining the extent and distribution of these schools is challenging. Here, we describe a novel use of a low-cost portable multibeam echosounder from a small vessel, which can concurrently measure detailed bathymetry and the distribution of mid-water targets with high spatial accuracy, regardless of light availability or water clarity. Fish abundance and biomass are not easily quantified by multibeam echosounders, so we developed a new metric for delineating the gridded horizontal distribution of school thickness, and assessed the metric's efficacy by examining its correlation with mean volume backscattering strength derived from a calibrated 38 kHz split-beam echosounder (R = 0.67). We measured the distribution of fish school thickness around clusters of large concrete modules of an artificial reef using a multibeam echosounder, complemented with underwater video to aid species identification. The mean distribution of school thickness was mapped around the reef field with generalized additive mixed models. Model spatial predictions indicated schools aggregated around module clusters, rather than individual modules. Dynamic schools of fish in relatively shallow coastal waters (~ 30 m) can be surveyed over 400,000 m² at 3 m s⁻¹ in just 60 min. Portable multibeam echosounders are an accessible and valuable addition to quantifying the dynamic distributions of coastal fishes around features with high vertical relief.

中文翻译：

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用便携式多波束回声测深仪表征学校礁鱼的三维分布

小型浮游鱼类的多物种学校是珊瑚礁和沿海基础设施的重要组成部分；但是，确定这些学校的范围和分布是具有挑战性的。在这里，我们描述了一种新颖的低成本小型多波束超声测深仪的使用方法，该技术来自一艘小型船只，可以同时测量详细的测深图和中空目标的分布，并具有很高的空间精度，而无需考虑光的可用性或净水度。鱼的丰度和生物量不易通过多波束回波测深仪量化，因此我们开发了一种新的度量标准来描绘学校厚度的网格水平分布，并通过检查该度量与校准后的38 kHz分裂平均声源的背向散射强度的相关性来评估该度量的有效性。光束测深仪（ř = 0.67）。我们使用多波束回声测深仪，结合水下视频以辅助物种识别，测量了人工鱼礁大型混凝土模块簇周围鱼群厚度的分布。用广义的加法混合模型将礁石场的平均厚度分布图绘制在礁区周围。模型空间预测表明，学校聚集在模块集群周围，而不是单个模块周围。在短短的60分钟内，可以在3 m s ^-1的相对较浅的沿海水域（〜30 m）中对超过40万m ²的鱼类进行动态调查。便携式多波束回声测深仪是量化具有高垂直起伏特征的沿海鱼类动态分布的一种便捷且有价值的工具。