The need to minimize bycatch of toothed whales (odontocetes) in gillnets has long been recognized, because they are often top predators and thus essential to ecosystem resilience. It is likely that a key to achieving this goal is the improvement of gillnet acoustic visibility, because these species use underwater sonar for orientation. Previous work on increasing gillnet detectability for echolocating animals by making the nets more recognizable has been based on trial and error, without understanding the fundamental acoustic properties of the tested modifications. Consequently, these studies have produced mixed and sometimes contradictory results. We systematically identified small, passive reflective objects that can improve the visibility of gillnets at a broad range of frequencies, i.e., for many odontocetes. We simulated the acoustic reflectivity of a wide range of materials in different shapes, sizes, and environmental conditions, with a focus on polymer materials. We verified the simulation results experimentally and calculated detection distances of the selected modifications. For example, if 8 mm acrylic glass spheres are attached to the net at intervals smaller than 0.5 m, the spheres have the same target strength (TS) at 130 kHz as the most recognizable part of a gillnet, the floatline. Modifications of the netting material itself, e.g., using barium sulfate additives, do not substantially increase the acoustic reflectivity of the net.

中文翻译：

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减少刺网中齿鲸误捕的最佳声学无源反射器的确定

人们早就认识到需要尽量减少刺网中齿鲸（齿鲸）的误捕，因为它们通常是顶级捕食者，因此对生态系统的恢复能力至关重要。实现这一目标的关键可能是提高刺网声能见度，因为这些物种使用水下声纳进行定位。以前通过使网更易识别来提高回声定位动物刺网可检测性的工作是基于反复试验，没有了解测试修改的基本声学特性。因此，这些研究产生了混合且有时相互矛盾的结果。我们系统地确定了小的、被动的反射物体，它们可以在广泛的频率范围内提高刺网的可见度，即对于许多齿鲸。我们模拟了各种不同形状、尺寸和环境条件的材料的声学反射率，重点是聚合物材料。我们通过实验验证了模拟结果并计算了所选修改的检测距离。例如，如果 8 mm 的丙烯酸玻璃球以小于 0.5 m 的间隔连接到网上，则这些球在 130 kHz 下具有与刺网最可识别部分（浮线）相同的目标强度 (TS)。网材料本身的改进，例如使用硫酸钡添加剂，基本上不会增加​​网的声反射率。我们通过实验验证了模拟结果并计算了所选修改的检测距离。例如，如果 8 mm 的丙烯酸玻璃球以小于 0.5 m 的间隔连接到网上，则这些球在 130 kHz 下具有与刺网最可识别部分（浮线）相同的目标强度 (TS)。网材料本身的改进，例如使用硫酸钡添加剂，基本上不会增加​​网的声反射率。我们通过实验验证了模拟结果并计算了所选修改的检测距离。例如，如果 8 mm 的丙烯酸玻璃球以小于 0.5 m 的间隔连接到网上，则这些球在 130 kHz 下具有与刺网最可识别部分（浮线）相同的目标强度 (TS)。网材料本身的改进，例如使用硫酸钡添加剂，基本上不会增加​​网的声反射率。