Incidental capture in gillnets is the most pressing threat for small cetaceans worldwide. One reason why small, echolocating cetaceans entangle in gillnets may be their inability to acoustically detect gillnets and classify them as obstacles. To increase the overall acoustic reflectivity as well as alter the perceived image to simulate an impenetrable barrier, small reflective objects – 8 mm wide acrylic glass spheres – were attached to standard gillnets. This study investigates the acoustic reflectivity of standard gillnets and modified gillnets with different numbers of spheres/m², at several angles of ensonification across a large frequency range. The acoustic reflectivity of standard gillnets is very low and decreases with angle of ensonification. Gillnets equipped with the spheres have substantially higher acoustic backscattering strength, and exhibit a positive relation between backscattering strength and inclination, i.e. gillnets ensonified from an angle have an even larger echo than when ensonified perpendicularly. Gillnets with sphere-sphere distance of 20 cm perform best, while the acoustic backscatter of gillnets with 40 cm and 60 cm sphere-distances is similar. The acoustic image (echogram) of the gillnet with spheres demonstrates a distinct highly visible acoustic pattern, potentially rendering the spheres an effective way to reduce bycatch of small cetaceans.

刺网的偶然捕获是全世界小型鲸目动物面临的最紧迫的威胁。小型、回声定位的鲸类动物纠缠在刺网中的一个原因可能是它们无法通过声学检测刺网并将其归类为障碍物。为了增加整体声学反射率并改变感知图像以模拟不可穿透的屏障，将小型反射物体 - 8 毫米宽的丙烯酸玻璃球 - 连接到标准刺网。本研究调查了标准刺网和具有不同球/平方米数的改进刺网的声学反射率，在大频率范围内的多个声化角度。标准刺网的声反射率非常低，并且随着声波角度的增加而降低。配备球体的刺网具有显着更高的声学反向散射强度，并且表现出后向散射强度和倾角之间的正相关关系，即从一个角度声波的刺网具有比垂直声波时更大的回波。球距为 20 cm 的刺网效果最好，而球距为 40 cm 和 60 cm 的刺网的声学反向散射相似。带有球体的刺网的声学图像（回声图）显示出明显的高度可见的声学图案，可能使球体成为减少小型鲸目动物兼捕的有效方法。而 40 cm 和 60 cm 球距的刺网的声学反向散射是相似的。带有球体的刺网的声学图像（回声图）显示出明显的高度可见的声学图案，可能使球体成为减少小型鲸目动物兼捕的有效方法。而 40 cm 和 60 cm 球距的刺网的声学反向散射是相似的。带有球体的刺网的声学图像（回声图）显示出明显的高度可见的声学图案，可能使球体成为减少小型鲸目动物兼捕的有效方法。