1. Juvenile silky sharks (Carcharhinus falciformis) regularly associate with floating objects yet the reasons driving this behaviour remain uncertain. Understanding the proportion of time that silky sharks spend associated with floating objects is essential for assessing the impacts of the extensive use of fish aggregating devices (FADs) in the tropical tuna purse‐seine fisheries, including increased probability of incidental capture and the potential of an ecological trap.
2. Previous studies provided insight into the amount of time that silky sharks spent at an individual FAD but were unable to assess neither the time spent between two associations nor the proportion of time spent associated/unassociated.
3. The percentage of time that juvenile silky sharks spend unassociated with floating objects was estimated through the analysis of horizontal movements of 26 silky sharks monitored with pop‐up archival tags. Under the assumption that a high association rate with drifting FADs would align the trajectories of tracked sharks with ocean surface currents, a novel methodology is proposed, based on the comparison of shark trajectories with simulated trajectories of passively drifting particles derived using a Lagrangian model.
4. Results revealed that silky shark trajectories were divergent from surface currents, and thus unassociated with FADs, for at least 30% of their time. The potential of the methodology and the results are discussed in the context of increasing FAD densities in the Indian Ocean.

中文翻译：

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漂流的物体能驱动脆弱的中上层鲨的运动吗？

1. 幼滑的鲨鱼（Carcharhinus falciformis）通常与漂浮物相关联，但导致这种行为的原因仍不确定。了解柔滑鲨鱼与漂浮物体相关的时间比例对于评估热带金枪鱼围网渔业中广泛使用鱼聚集装置（FAD）的影响至关重要，包括偶然捕获的可能性增加和捕捞的可能性生态陷阱。
2. 先前的研究提供了有关鲨鱼在单个FAD上花费的时间的见解，但无法评估两个协会之间花费的时间，也无法评估花费在关联/不关联上的时间比例。
3. 通过分析带有弹出式归档标签的26个丝质鲨的水平运动，可以估算出幼稚的丝质鲨与漂浮物无关的时间百分比。假设与漂移的FAD的高关联率将使跟踪的鲨鱼的轨迹与海面洋流对齐，基于鲨鱼的轨迹与使用拉格朗日模型得出的被动漂移粒子的模拟轨迹的比较，提出了一种新的方法。
4. 结果表明，丝鲨的轨迹在至少30％的时间内与表面流不同，因此与FAD无关。在印度洋不断增加的FAD密度的背景下，讨论了该方法的潜力和结果。