ABSTRACT

Sharks are threatened by several human activities that impact their distribution and abundance. A great proportion of shark captures happen as incidental capture (bycatch) by fisheries and in beach nets. Recent studies have focused on reducing these captures by exploiting technologies that target the sharks’ electrosensory system, obtaining contrasting results. This study investigates the effect of a strong neodymium magnet and pulsed magnetic fields (PMFs) on captive sand tiger sharks (Carcharias taurus) through the analysis of their behavioural responses. Firstly, individuals were presented with the magnet in combination with different types of food. The magnet did not influence the sharks’ behaviours, while an effect of the food type emerged. Secondly, PMFs were generated through a pulsed electric current induced within a solenoid associated with a PVC structure. The PMFs affected some of the sharks’ behaviours, both near (<2 m) and at a distance (>2 m) from the source. The results suggest that strong magnets are inefficient in deterring sand tiger sharks, while PMFs could be a promising alternative. This study confirms how the efficacy of shark repellents may be affected by factors such as the type of electrosensory stimuli, the species involved, and the context in which the interaction takes place.

摘要

鲨鱼受到几种人类活动的威胁，这些活动会影响鲨鱼的分布和数量。很大一部分鲨鱼的捕捞是由于渔业和沙滩网的偶然捕捞（兼捕）而发生的。最近的研究集中在通过开发针对鲨鱼电感应系统的技术来减少捕获，从而获得对比结果。这项研究调查了强钕磁铁和脉冲磁场（PMF）对圈养沙虎鲨（Carcharias taurus）的影响）通过对其行为反应的分析。首先，向人们展示了结合不同类型食物的磁铁。磁铁并没有影响鲨鱼的行为，但出现了食物类型的影响。其次，PMF是通过在与PVC结构相关的螺线管内感应的脉冲电流产生的。PMF影响了某些鲨鱼的行为，无论是在其附近（<2 m）还是在与源之间的距离（> 2 m）。结果表明，强磁体无法有效地阻止沙虎鲨，而PMF可能是有前途的替代方法。这项研究证实了鲨鱼驱避剂的功效如何受到诸如电感应刺激的类型，所涉及的物种以及相互作用发生的环境等因素的影响。